About HDLRuby
HDLRuby is a library for describing and simulating digital electronic systems.
Note:
If you are new to HDLRuby, it is recommended that you consult first the following tutorial (even if you are a hardware person):
Install:
The recommended installation method is from rubygem as follows:
gem install HDLRuby
Developers willing to contribute to HDLRuby can install the sources from GitHub as follows:
git clone HDLRuby
Warning:
- This is still preliminary work which may change before we release a stable version.
- It is highly recommended to have both basic knowledge of the Ruby language and hardware description languages before using HDLRuby.
Compiling HDLRuby descriptions
Using the HDLRuby compiler
'hdrcc' is the HDLRuby compiler. It takes as input an HDLRuby file, checks it, and can produce as output a Verilog HDL, VHDL, or a YAML low-level description of HW components but it can also simulate the input description.
Usage:
hdrcc [options] <input file> <output directory>
Where:
-
options
is a list of options -
<input file>
is the initial file to compile (mandatory) -
<output directory>
is the directory where the generated files will be put
Options | |
---|---|
-I, --interactive |
Run in interactive mode |
-y, --yaml |
Output in YAML format |
-v, --verilog |
Output in Verilog HDL format |
-V, --vhdl |
Output in VHDL format |
-s, --syntax |
Output the Ruby syntax tree |
-C, --clang |
Output the C code of the standalone simulator |
-S, --sim |
Perform the simulation with the default engine |
--csim |
Perform the simulation with the standalone engine |
--rsim |
Perform the simulation with the Ruby engine |
--rcsim |
Perform the simulation with the Hybris engine |
--vcd |
Make the simulator generate a VCD file |
-d, --directory |
Specify the base directory for loading the HDLRuby files |
-D, --debug |
Set the HDLRuby debug mode |
-t, --top system |
Specify the top system describing the circuit to compile |
-p, --param x,y,z |
Specify the generic parameters |
--get-samples |
Copy the sample directory (hdr_samples) to current one, then exit |
--version |
Show the version number, then exit |
-h, --help |
Show the help message |
Notes:
-
If no top system is given, it is automatically looked for from the input file.
-
If no option is given, it simply checks the input file.
-
If you are new to HDLRuby, or if you want to see how new features work, we strongly encourage to get a local copy of the test HDLRuby sample using:
hdrcc --get-samples
Then in your current directory (folder) the
hdr_samples
subdirectory will appear that contains several HDLRuby example files. For details about the samples can be found there: samples.
Examples:
- Compile system named
adder
fromadder.rb
input file and generate a low-level YAML description into directoryadder
:
hdrcc --yaml --top adder adder.rb adder
- Compile
adder.rb
input file and generate a low-level Verilog HDL description into directoryadder
:
hdrcc -v adder.rb adder
- Compile system
adder
whose bit width is generic fromadder_gen.rb
input file to a 16-bit circuit low-level VHDL description into directoryadder
:
hdrcc -V -t adder --param 16 adder_gen.rb adder
- Compile system
multer
with inputs and output bit width is generic frommulter_gen.rb
input file to a 16x16->32-bit circuit whose low-level YAML description into directorymulter
:
hdrcc -y -t multer -p 16,16,32 multer_gen.rb multer
- Simulate the circuit described in file
counter_bench.rb
using the default simulation engine and putting the simulator's files in directorycounter
:
hdrcc -S counter_bench.rb counter
As a policy, the default simulation engine is set to the fastest one (currently it is the hybrid engine).
- Run in interactive mode.
hdrcc -I
- Run in interactive mode using pry as UI.
hdrcc -I pry
Using HDLRuby in interactive mode
When running in interactive mode, the HDLRuby framework starts a REPL prompt and creates a working directory called 'HDLRubyWorkspace'. By default, the REPL is 'irb', but it can be set to 'pry'. Within this prompt, HDLRuby code can be written like in an HDLRuby description file. However, to process this code the following commands are added:
- Compile an HDLRuby module:
hdr_make(<module>)
- Generate and display the IR of the compiled module in YAML form:
hdr_yaml
- Regenerate and display the HDLRuby description of the compiled module:
hdr_hdr
- Generate and output in the working directory the Verilog HDL RTL of the compiled module:
hdr_verilog
- Generate and output in the working directory the Verilog HDL RTL of the compiled module:
hdr_vhdl
- Simulate the compiled module:
hdr_sim
HDLRuby programming guide
HDLRuby has been designed to bring the high flexibility of the Ruby language to hardware descriptions while ensuring that they remain synthesizable. In this context, all the abstractions provided by HDLRuby are in the way of describing hardware, but not in its execution model, this latter being RTL by construction.
The second specificity of HDLRuby is that it supports natively all the features of the Ruby language.
Notes:
- It is still possible to extend HDLRuby to support hardware descriptions of a higher level than RTL, please refer to section Extending HDLRuby for more details.
- In this document, HDLRuby constructs will often be compared to their Verilog HDL or VHDL equivalents for simpler explanations.
Introduction
This introduction gives a glimpse of the possibilities of the language. However, we do recommend consulting the section about the high-level programming features to have a more complete view of the advanced possibilities of this language.
At first glance, HDLRuby appears like any other HDL (like Verilog HDL or VHDL), for instance, the following code describes a simple D-FF:
system :dff do
bit.input :clk, :rst, :d
bit.output :q
par(clk.posedge) do
q <= d & ~rst
end
end
As can be seen in the code above, system
is the keyword used for describing a digital circuit. This keyword is the equivalent of the Verilog HDL module
. In such a system, signals are declared using a <type>.<direction>
construct where type
is the data type of the signal (e.g., bit
as in the code above) and direction
indicates if the signal is an input, an output, an inout or an inner one; and executable blocks (similar to always
block of Verilog HDL) are described using the par
keyword when they are parallel and seq
when they are sequential (i.e., with respectively non-blocking and blocking assignments).
After such a system has been defined, it can be instantiated. For example, a single instance of the dff
system named dff0
can be declared as follows:
dff :dff0
The ports of this instance can then be accessed to be used like any other signals, e.g., dff0.d
for accessing the d
input of the FF.
Several instances can also be declared in a single statement. For example, a 2-bit counter based on the previous dff
circuits can be described as follows:
system :counter2 do
input :clk,:rst
output :q
dff [ :dff0, :dff1 ]
dff0.clk <= clk
dff0.rst <= rst
dff0.d <= ~dff0.q
dff1.clk <= ~dff0.q
dff1.rst <= rst
dff1.d <= ~dff1.q
q <= dff1.q
end
The instances can also be connected while being declared. For example, the code above can be rewritten as follows:
system :counter2 do
input :clk, :rst
output :q
dff(:dff0).(clk: clk, rst: rst, d: ~dff0.q)
dff(:dff1).(~dff0.q, rst, ~dff1.q, q)
end
In the code above, two possible connection methods are shown: for dff0
ports are connected by name, and for dff1
ports are connected by declaration order. Please notice that it is also possible to connect only a subset of the ports while declaring, and to reconnect already connected ports in further statements.
While a circuit can be generated from the code given above, a benchmark must
be provided to test it. Such a benchmark is described by constructs called
timed behavior that give the evolution of signals depending on the time.
For example, the following code simulates the previous D-FF for 4 cycles
of 20ns each, with a reset on the first cycle, set of signal d
to 1 for
the third cycle and set this signal to 0 for the last.
system :dff_bench do
dff :dff0
timed do
dff0.clk <= 0
dff0.rst <= 1
!10.ns
dff0.clk <= 1
!10.ns
dff0.clk <= 0
dff0.rst <= 0
dff0.d <= 1
!10.ns
dff0.clk <= 1
!10.ns
dff0.clk <= 0
!10.ns
dff0.clk <= 1
!10.ns
dff0.clk <= 0
dff0.d <= 1
!10.ns
dff0.clk <= 1
!10.ns
end
end
The code describing a dff
given above is not much different from its equivalent in any other HDL. However, HDLRuby provides several features for achieving higher productivity when describing hardware. We will now describe a few of them.
First, several syntactic sugars exist that allow shorter code, for instance, the following code is strictly equivalent to the previous description of dff
:
system :dff do
input :clk, :rst, :d
output :q
(q <= d & ~rst).at(clk.posedge)
end
Then, it often happens that a system will end up with only one instance. In such a case, the system declaration can be omitted, and an instance can be directly declared as follows:
instance :dff_single do
input :clk, :rst, :d
output :q
(q <= d & ~rst).at(clk.posedge)
end
In the example above, dff_single
is an instance describing, again, a
D-FF, but whose system is anonymous.
Furthermore, generic parameters can be used for anything in HDLRuby. For instance, the following code describes an 8-bit register without any parameterization:
system :reg8 do
input :clk, :rst
[7..0].input :d
[7..0].output :q
(q <= d & [~rst]*8).at(clk.posedge)
end
But it is also possible to describe a register of arbitrary size as follows, where n
is the parameter giving the number of bits of the register:
system :regn do |n|
input :clk, :rst
[n-1..0].input :d
[n-1..0].output :q
(q <= d & [~rst]*n).at(clk.posedge)
end
Or, even further, it is possible to describe a register of arbitrary type (not only bit vectors) as follows:
system :reg do |typ|
input :clk, :rst
typ.input :d
typ.output :q
(q <= d & [~rst]*typ.width).at(clk.posedge)
end
Wait... I have just realized that D-FF without any inverted output does not look very serious. So, let us extend the existing dff
to provide an inverted output. There are three ways for doing this. First, inheritance can be used: a new system is built inheriting from dff
as it is done in the following code.
system :dff_full, dff do
output :qb
qb <= ~q
end
The second possibility is to modify dff
afterward. In HDLRuby, this is achieved using the open
method as it is done in the following code:
dff.open do
output :qb
qb <= ~q
end
The third possibility is to modify directly a single instance of dff
which requires an inverted output, using again the open
method, as in the following code:
# Declare dff0 as an instance of dff
dff :dff0
# Modify it
dff0.open do
output :qb
qb <= ~q
end
In this latter case, only dff0
will have an inverted output, the other instances of dff
will not change.
Now assuming we opted for the first solution, we have now dff_full
, a highly advanced D-FF with such unique features as an inverted output. So, we would like to use it in other designs, for example, a shift register of n
bits. Such a system will include a generic number of dff_full
instances and can be
described as follows making use of the native Ruby method each_cons
for connecting them:
system :shifter do |n|
input :clk, :rst
input :i0
output :o0, :o0b
# Instantiating n D-FF
[n].dff_full :dffIs
# Connect the clock and the reset.
dffIs.each { |ff| ff.clk <= clk ; ff.rst <= rst }
# Interconnect them as a shift register
dffIs[0..-1].each_cons(2) { |ff0,ff1| ff1.d <= ff0.q }
# Connects the input and output of the circuit
dffIs[0].d <= i0
o0 <= dffIs[-1].q
o0b <= dffIs[-1].qb
end
As can be seen in the above examples, in HDLRuby, any construct is an object and therefore include methods. For instance, declaring a signal of a given type
and direction (input, output, or inout) is done as follows so that direction
is a method of the type, and the signal names are the arguments of this method (symbols or string are supported.)
<<span class="pl-en">type</span>><span class="pl-kos">.</span><<span class="pl-en">direction</span>> <<span class="pl-en">list</span> <span class="pl-en">of</span> <span class="pl-en">symbols</span> <span class="pl-en">representing</span> <span class="pl-en">the</span> <span class="pl-en">signal</span>><span class="pl-en"></span>
Of course, if you do not need to use the specific component dff_full
you can describe a shift register more simply as follows:
system :shifter do |n|
input :clk, :rst
input :i0
output :o0
[n].inner :sh
par (clk.posedge) do
hif(rst) { sh <= 0 }
helse { sh <= [sh[n-2..0], i0] }
end
o0 <= sh[n-1]
end
Now, let us assume you want to design a circuit that performs a sum of products of several inputs with constant coefficients. For the case of 4 16-bit signed inputs and given coefficients as 3, 4, 5, and 6. The corresponding basic code could be as follows:
system :sumprod_16_3456 do
signed[16].input :i0, :i1, :i2, :i3
signed[16].output :o
o <= i0*3 + i1*4 + i2*5 + i3*6
end
The description above is straightforward, but it would be necessary to rewrite it if another circuit with different bit widths or coefficients is to be designed. Moreover, if the number of coefficients is large an error in the expression will be easy to make and hard to find. A better approach would be to use a generic description of such a circuit as follows:
system :sumprod do |typ,coefs|
typ[coefs.size].input :ins
typ.output :o
o <= coefs.each_with_index.reduce(_b0) do |sum,(coef,i)|
sum + ins[i]*coef
end
end
In the code above, there are two generic parameters,
typ
, which indicates the data type of the circuit, and coefs
, which is assumed to be an array of coefficients. Since the number of inputs depends on the number of provided coefficients, it is declared as an array of width
bit signed whose size is equal to the number of coefficients.
The description of the sum of products may be more difficult to understand for people not familiar with the Ruby language. The each_with_index
method iterates over the coefficients adding their index as an iteration variable, the resulting operation (i.e., the iteration loop) is then modified by the reduce
method that accumulates the code passed as arguments. This code, starting by |sum,coef,i|
simply performs the addition of the current accumulation result (sum
) with the product of the current coefficient (coef
) and input (ins[i]
, where i
is the index) in the iteration. The argument _b0
initializes the sum to 0
.
While slightly longer than the previous description, this description allows declaring a circuit implementing a sum of products with any bit width and any number of coefficients. For instance, the following code describes a signed 32-bit sum of products with 16 coefficients (just random numbers here).
sumprod(signed[32], [3,78,43,246, 3,67,1,8, 47,82,99,13, 5,77,2,4]).(:my_circuit)
As seen in the code above, when passing a generic argument for instantiating a generic system, the name of the instance is put between brackets for avoiding confusion.
While the description sumprod
is already usable in a wide range of cases, it still uses standard addition and multiplication. However, there are cases where specific components are to be used for these operations, either for sake of performance, compliance with constraints, or because functionally different operations are required (e.g., saturated computations). This can be solved by using functions implementing such computation in place of operators, for example as follows:
system :sumprod_func do |typ,coefs|
typ[coefs.size].input ins
typ.output :o
o <= coefs.each_with_index.reduce(_b0) do
|sum,(coef,i)|
add(sum, mult(ins[i]*coef))
end
end
Where add
and mult
are functions implementing the required specific operations. HDLRuby functions are equivalent to the Verilog HDL ones. In our example, an addition that saturates at 1000 could be described as follows:
function :add do |x,y|
inner :res
seq do
res <= x + y
(res <= 1000).hif(res > 1000)
end
end
With HDLRuby functions, the result of the last statement in the return value, in this case, that will be the value of res. The code above is also an example of the usage of the postfixed if statement, it is an equivalent of the following code:
<span class="pl-en">hif</span><span class="pl-kos">(</span><span class="pl-en">res</span>><span class="pl-c1">1000</span><span class="pl-kos">)</span> <span class="pl-kos">{</span> <span class="pl-en">res</span> <= <span class="pl-c1">1000</span> <span class="pl-kos">}</span>
With functions, it is enough to change their content to obtain a new kind of circuit without changing the main code. This approach suffers from two drawbacks though: first, the level of saturation is hard coded in the function, and second, it would be preferable to be able to select the function to execute instead of modifying its code. For the first problem, a simple approach is to add an argument to the function given the saturation level. Such an add function would therefore be as follows:
function :add do |max, x, y|
inner :res
seq do
res <= x + y
(res <= max).hif(res > max)
end
end
It would however be necessary to add this argument when invoking the function, e.g., add(1000,sum,mult(...))
. While this argument is relevant for addition with saturation, it is not for the other kind of addition operations, and hence, the code of sumprod
is not general-purpose any longer.
HDLRuby provides two ways to address such issues. First, it is possible to pass code as an argument. In the case of sumprod
, it would then be enough to add two arguments that perform the required addition and multiplication. The example is below:
system :sumprod_proc do |add,mult,typ,coefs|
typ[coefs.size].input ins
typ.output :o
o <= coefs.each_with_index.reduce(_b0) do
|sum,(coef,i)|
add.(sum, mult.(ins[i]*coef))
end
end
Note:
- With HDLRuby, when some code is passed as an argument, it is invoked using the
.()
operator, and not simple parenthesis-like functions.
Assuming the addition with saturation is now implemented by a function named add_sat
and a multiplication with saturation is implemented by a function named mult_sat
(with similar arguments), a circuit implementing a signed 16-bit sum of product saturating at 1000 with 16 coefficients could be described as follows:
sumprod_proc(
proc { |x,y| add_sat(1000,x,y) },
proc { |x,y| mult_sat(1000,x,y) },
signed[64],
[3,78,43,246, 3,67,1,8,
47,82,99,13, 5,77,2,4]).(:my_circuit)
As seen in the example above, a piece of code is passed as an argument using the proc keyword.
A second possible approach provided by HDLRuby is to declare a new data type with redefined addition and multiplication operators. For the case of a 16-bit saturated addition and multiplication the following generic data type can be defined (for signed computations):
signed[16].typedef(:sat16_1000)
sat16_1000.define_operator(:+) do |x,y|
tmp = x + y
mux(tmp > 1000,tmp,1000)
end
end
In the code above, the first line defines the new type sat16_1000
to be 16-bit signed and the remaining overloads (redefines) the +
operator for this type (the same should be done for the *
operator).
Then, the initial version of sumprod
can be used with this type to achieve saturated computations as follows:
sumprod(sat16_1000,
[3,78,43,246, 3,67,1,8,
47,82,99,13, 5,77,2,4]).(:my_circuit)
It is also possible to declare a generic type. For instance, a generic signed type with saturation can be declared as follows:
typedef :sat do |width, max|
signed[width]
end
sat.define_operator(:+) do |width,max, x,y|
tmp = x + y
mux(tmp > max, tmp, max)
end
end
Note:
- The generic parameters have also to be declared for the operator redefinitions.
With this generic type, the circuit can be declared as follows:
sumprod(sat(16,1000),
[3,78,43,246, 3,67,1,8,
47,82,99,13, 5,77,2,4]).(:my_circuit)
Lastly note, HDLRuby is also a language with supports reflection for
all its constructs. For example, the system of an instance can be accessed
using the systemT
method, and this latter can be used to create
other instances. For example, previously, dff_single
was declared with
an anonymous system (i.e., it cannot be accessed by name). This system
can however be used as follows to generate another instance:
dff_single.systemT.instantiate(:dff_not_single)
In the above example, dff_not_single
is declared to be an instance
of the same system as dff_single
.
This reflection capability can also be used for instance, for accessing the
data type of a signal (sig.type
), but also the current basic block
(cur_block
), the current process (cur_behavior
) and so on.
The standard library of HDLRuby includes several hardware constructs
like finite state machine descriptors and is mainly based on using these
reflection features.
How does HDLRuby work
Contrary to descriptions in high-level HDL like SystemVerilog, VHDL, or SystemC, HDLRuby descriptions are not software-like descriptions of hardware but are programs meant to produce hardware descriptions. In other words, while the execution of a common HDL code will result in some simulation of the described hardware, the execution of HDLRuby code will result in some low-level hardware description. This low-level description is synthesizable and can also be simulated like any standard hardware description. This decoupling of the representation of the hardware from the point of view of the user (HDLRuby), and the actual hardware description (HDLRuby::Low) makes it possible to provide the user with any advanced software features without jeopardizing the synthesizability of the actual hardware description.
For that purpose, each construct in HDLRuby is not a direct description of some hardware construct, but a program that generates the corresponding description. For example, let us consider the following line of code of HDLRuby describing the connection between signal a
and signal b
:
<span class="pl-en">a</span> <= <span class="pl-en">b</span>
Its execution will produce the actual hardware description of this connection as an object of the HDLRuby::Low library — in this case, an instance of the HDLRuby::Low::Connection
class. Concretely, an HDLRuby system is described by a Ruby block, and the instantiation of this system is performed by executing this block. The actual synthesizable description of this hardware is the execution result of this instantiation.
From there, we will describe in more detail each construct of HDLRuby.
Naming rules
Several constructs in HDLRuby are referred to by name, e.g., systems and signals. When such constructs are declared, their names are to be specified by Ruby symbols starting with a lowercase. For example, :hello
is a valid name declaration, but :Hello
is not.
After being declared, the construct can be referred to by using the name directly (i.e., without the :
of Ruby symbols). For example, if a construct
has been declared with :hello
as the name, it will be afterward referred to by hello
.
Systems and signals
A system represents a digital system and corresponds to a Verilog HDL module. A system has an interface comprising input, output, and inout signals, and includes structural and behavioral descriptions.
A signal represents a state in a system. It has a data type and a value, the latter varying with time. HDLRuby signals can be viewed as abstractions of both wires and registers in a digital circuit. As a general rule, a signal whose value is explicitly set all the time models a wire, otherwise it models a register.
Declaring an empty system
A system is declared using the keyword system
. It must be given a Ruby symbol for its name and a block that describe its content. For instance, the following code describes an empty system named box
:
system(:box) {}
Notes:
- Since this is Ruby code, the body can also be delimited by the
do
andend
Ruby keywords (in which case the parentheses can be omitted) are as follows:
system :box does
end
- Names in HDLRuby are natively stored as Ruby symbols, but strings can
also be used, e.g.,
system("box") {}
is also valid.
Declaring a system with an interface
The interface of a system can be described anywhere in its body, but it is recommended to do it at its beginning. This is done by declaring input, output, or inout signals of given data types as follows:
<<span class="pl-en">data</span> <span class="pl-en">type</span>><span class="pl-kos">.</span><<span class="pl-en">direction</span>> <<span class="pl-en">list</span> <span class="pl-en">of</span> <span class="pl-en">colon</span>-<span class="pl-en">preceded</span> <span class="pl-en">names</span>><span class="pl-en"></span>
For example, declaring a 1-bit input signal named clk
can be declared as follows:
bit.input :clk
Now, since bit
is the default data type in HDLRuby, it can be omitted as follows:
input :clk
The following is a more complete example: it is the code of a system describing an 8-bit data, 16-bit address memory whose interface includes a 1-bit input
clock (clk
), a 1-bit signal for selecting reading or writing access (rwb
), a 16-bit address input (addr
), and an 8-bit data inout — the remaining of the code describes the content and the behavior of the memory.
system :mem8_16 do
input :clk, :rwb
[15..0].input :addr
[7..0].inout :data
bit[7..0][2**16].inner :content
par(clk.posedge) do
hif(rwb) { data <= content[addr] }
helse { content[addr] <= data }
end
end
Structural description in a system
In a system, structural descriptions consist of subsystems and interconnections among them.
A subsystem is obtained by instantiating an existing system as follows, where <system name>
is the name of the system to instantiate (without any colon):
<<span class="pl-en">system</span> <span class="pl-en">name</span>> <span class="pl-pds">:<instance</span> <span class="pl-en">name</span>><span class="pl-en"></span>
For example, system mem8_16
declared in the previous section can be instantiated as follows:
mem8_16 :mem8_16I
It is also possible to declare multiple instances of the same system at a time as follows:
<<span class="pl-en">system</span> <span class="pl-en">name</span>> <span class="pl-kos">[</span><span class="pl-en">list</span> <span class="pl-en">of</span> <span class="pl-en">colon</span>-<span class="pl-en">separated</span> <span class="pl-en">instance</span> <span class="pl-en">names</span><span class="pl-kos">]</span>
For example, the following code declares two instances of system mem8_16
:
mem8_16 [ :mem8_16I0, :mem8_16I1 ]
Interconnecting instances may require internal signals in the system.
Such signals are declared using the inner
direction.
For example, the following code declares a 1-bit inner signal named w1
and a 2-bit inner signal named w2
:
inner :w1
[1..0].inner :w2
If the signal is not meant to be changed, it can be declared using the constant
keyword instead of inner
.
A connection between signals is done using the arrow operator <=
as follows:
<<span class="pl-en">destination</span>> <= <<span class="pl-en">source</span>><span class="pl-en"></span>
The <destination>
must be a reference to a signal, and the <source>
can be any expression.
For example, the following code connects signal w1
to signal ready
and signal clk
to the first bit of signal w2
:
ready <= w1
w2[0] <= clk
As another example, the following code connects to the second bit of w2
the output of an AND operation between clk
and rst
as follows:
w2[1] <= clk & rst
The signals of an instance can be connected through the arrow operator too, provided they are properly referred to. One way to refer to them is to use the dot operator .
on the instance as follows:
<<span class="pl-en">instance</span> <span class="pl-en">name</span>><span class="pl-kos">.</span><<span class="pl-en">signal</span> <span class="pl-en">name</span>>
For example, the following code connects signal clk
of instance mem8_16I
to signal clk
of the current system:
mem8_16I.clk <= clk
It is also possible to connect multiple signals of an instance using the call operator .()
as follows, where each target can be any expression:
<<span class="pl-en">instance</span> <span class="pl-en">name</span>><span class="pl-en"></span><span class="pl-kos">.</span><span class="pl-kos">(</span><<span class="pl-en">signal</span> <span class="pl-en">name0</span>>: <<span class="pl-en">target0</span>><span class="pl-kos">,</span> ...<span class="pl-kos">)</span>
For example, the following code connects signals clk
and rst
of instance
mem8_16I
to signals clk
and rst
of the current system. As seen in this example, this method allows partial connection since the address and the data buses are not connected yet.
mem8_16I.(clk: clk, rst: rst)
This last connection method can be used directly while declaring an instance.
For example, mem8_16I
could have been declared and connected to clk
and rst
as follows:
mem8_16(:mem8_16I).(clk: clk, rst: rest)
To summarize this section, here is a structural description of a 16-bit memory made of two 8-bit memories (or equivalent) sharing the same address bus, and using respectively the lower and the higher 8-bits of the data bus:
system :mem16_16 do
input :clk, :rwb
[15..0].input :addr
[15..0].inout :data
mem8_16(:memL).(clk: clk, rwb: rwb, addr: addr, data: data[7..0])
mem8_16(:memH).(clk: clk, rwb: rwb, addr: addr, data: data[15..8])
end
And here is an equivalent code using the arrow operator:
system :mem16_16 do
input :clk, :rwb
[15..0].input :addr
[15..0].inout :data
mem8_16 [:memL, :memH]
memL.clk <= clk
memL.rwb <= rwb
memL.addr <= addr
memL.data <= data[7..0]
memH.clk <= clk
memH.rwb <= rwb
memH.addr <= addr
memH.data <= data[15..8]
end
Initialization of signals
Output, inner and constant signals of a system can be initialized when declared using the following syntax in place of the usual name of the signal:
<<span class="pl-en">signal</span> <span class="pl-en">name</span>>: <<span class="pl-en">intial</span> <span class="pl-en">value</span>><span class="pl-en"></span>
For example, a single-bit inner signal named sig
can be initialized to 0 as follows:
inner sig: 0
As another example, an 8-bit 8-word ROM could be declared and initialized as follows:
bit[8][-8] rom: [ 0,1,2,3,4,5,6,7 ]
Scope in a system
General scopes
The signals of the interface of signals are accessible from anywhere in an HDLRuby description. This is not the case for inner signals and instances: they are accessible only within the scope they are declared in.
A scope is a region of the code where locally declared objects are accessible. Each system has its scope that cannot be accessible from another part of an HDLRuby description. For example, in the following code signals d
and qb
as well as instance dffI
cannot be accessed from outside system div2
:
system :div2 do
input :clk
output :q
inner :d, :qb
d <= qb
dff_full(:dffI).(clk: clk, d: d, q: q, qb: qb)
For robustness or, readability purpose, it is possible to add inner scope inside the existing scope using the sub
keyword as follows:
sub do
<code>
end
For example, in the code below signal sig
is not accessible from outside the additional inner scope of system sys
system :sys do
...
sub
inner :sig
<sig is accessible here>
end
<sig is not accessible from here>
end
It is also possible to add an inner scope within another inner scope as follows:
system :sys do
...
sub
inner :sig0
<sig0 is accessible here>
sub
inner :sig1
<sig0 and sig1 are accessible here>
end
<sig1 is not accessible here>
end
<neither sig0 nor sig1 are accessible here>
end
Within the same scope, it is not possible to declare multiple signals or instances with the same name. However, it is possible to declare a signal or an instance with a name identical to one previously declared outside the scope: the inner-most declaration will be used.
Named scopes
It is possible to declare a scope with a name as follows:
sub :> do
<code>
end
Where:
-
<name>
is the name of the scope. -
<code>
is the code within the scope.
Contrary to the case of scopes without a name, signals, and instances declared within a named scope can be accessed outside using this name as a reference. For example, in the code below signal sig
declared within scope named scop
is accessed outside it using scop.sig
:
sub :scop do
inner :sig
...
end
...
scop.sig <= ...
Behavioral description in a system.
In a system, parallel behavioral descriptions are declared using the par
keyword, and sequential behavioral descriptions are declared using the seq
keyword. They are the equivalent of the Verilog HDL always
blocks.
A behavior is made of a list of events (the sensitivity list) upon which it is activated, and a list of statements. A behavior is declared as follows:
par <list of events> do
<list of statements>
end
In addition, it is possible to declare inner signals within an execution block. While such signals will be physically linked to the system, they are only accessible within the block they are declared into. This permits a tighter scope for signals, which improves the readability of the code and make it possible to declare several signals with identical names provided their respective scopes are different.
An event represents a specific change in the state of a signal.
For example, a rising edge of a clock signal named clk
will be represented by the event clk.posedge
. In HDLRuby, events are obtained directly from
expressions using the following methods: posedge
for a rising edge, negedge
for a falling edge, and edge
for any edge.
Events are described in more detail in section Events.
When one of the events of the sensitivity list of a behavior occurs, the behavior is executed, i.e., each of its statements is executed in sequence. A statement can represent a data transmission to a signal, a control flow, a nested execution block, or the declaration of an inner signal (as stated earlier). Statements are described in more detail in section statements. In this section, we focus on the transmission statements and the block statements.
A transmission statement is declared using the arrow operator <=
as follows:
<<span class="pl-en">destination</span>> <= <<span class="pl-en">source</span>><span class="pl-en"></span>
The <destination>
must be a reference to a signal, and the <source>
can be any expression. A transmission has therefore the same structure as a connection. However, its execution model is different: whereas a connection is continuously executed, a transmission is only executed during the execution of its block.
A block comprises a list of statements. It is used for adding hierarchy to a behavior. Blocks can be either parallel or sequential, i.e., their transmission statements are respectively non-blocking or blocking. By default, a top block is created when declaring a behavior, and it inherits from its execution mode. For example, with the following code, the top block of the behavior is sequential.
system :with_sequential_behavior do
seq do
<list of statements>
end
end
It is possible to declare new blocks within an existing block.
For declaring a sub-block with the same execution mode as the upper one, the keyword sub
is used. For example, the following code declares a sub-block within a sequential block, with the same execution mode:
system :with_sequential_behavior do
seq do
<list of statements>
sub do
<list of statements>
end
end
end
A sub-block can also have a different execution mode if it is declared using seq
, which will force sequential execution mode and par
which will force parallel execution mode. For example, in the following code a parallel sub-block is declared within a sequential one:
system :with_sequential_behavior do
seq do
<list of statements>
par do
<list of statements>
end
end
end
Sunblocks have their scope so that it is possible to declare signals without colliding with existing ones. For example, it is possible to
declare three different inner signals all called sig
as follows:
...
par(<sensibility list>) do
inner :sig
...
sub do
inner :sig
...
sub do
inner :sig
...
end
end
...
end
To summarize this section, here is a behavioral description of a 16-bit shift register with asynchronous reset (hif
and helse
are keywords used for specifying hardware if and else control statements).
system :shift16 do
input :clk, :rst, :din
output :dout
[15..0].inner :reg
dout <= reg[15] # The output is the last bit of the register.
par(clk.posedge) do
hif(rst) { reg <= 0 }
helse do
reg[0] <= din
reg[15..1] <= reg[14..0]
end
end
end
In the example above, the order of the transmission statements is of no consequence. This is not the case for the following example, which implements the same register using a sequential block. In this second example, putting the statement reg[0] <= din
in the last place would have led to an invalid functionality for a shift register.
system :shift16 do
input :clk, :rst, :din
output :dout
[15..0].inner :reg
dout <= reg[15] # The output is the last bit of the register.
par(clk.posedge) do
hif(rst) { reg <= 0 }
helse seq do
reg[0] <= din
reg <= reg[14..0]
end
end
end
Note:
-
helse seq
ensures that the block of the hardware else is in sequential mode. -
hif(rst)
could also have been set to sequential mode as follows:<span class="pl-en">hif</span> <span class="pl-en">rst</span><span class="pl-kos">,</span> <span class="pl-en">seq</span> <span class="pl-k">do</span> <span class="pl-en">reg</span> <= <span class="pl-c1">0</span> <span class="pl-k">end</span>
-
Parallel mode can be set the same way using
par
.
Extra features for the description of behaviors
Single-statement behaviors
It often happens that a behavior contains only one statement. In such a case, the description can be shortened using the at
operator as follows:
( statement ).at(<list of events>)
For example, the following two code samples are equivalent:
par(clk.posedge) do
a <= b+1
end
( a <= b+1 ).at(clk.posedge)
For sake of consistency, this operator can also be applied to block statements as follows, but it is probably less readable than the standard declaration of behaviors:
( seq do
a <= b+1
c <= d+2
end ).at(clk.posedge)
Insertion of statements at the beginning of a block
By default, the statements of a block are added in order of appearance in the code. However, it is also possible to insert statements at the top of the current block using the unshift command within a block as follows:
unshift do
<list of statements>
end
For example, the following code inserts two statements at the beginning of the current block:
par do
x <= y + z
unshift do
a <= b - c
u <= v & w
end
end
The code above will result in the following block:
par do
a <= b - c
u <= v & w
x <= y + z
end
Note:
- While of no practical use for simple circuit descriptions, this feature can be used in advanced generic component descriptions.
Reconfiguration
In HDLRuby, dynamically reconfigurable devices are modeled by instances having more than one system. Adding systems to an instance is done as follows:
<<span class="pl-en">instance</span>><span class="pl-kos">.</span><span class="pl-en">choice</span><span class="pl-kos">(</span><<span class="pl-en">list</span> <span class="pl-en">of</span> <span class="pl-en">named</span> <span class="pl-en">systems</span>><span class="pl-c1"></span><span class="pl-kos">)</span>
For example, assuming systems sys0
, sys1
, and sys2
have been previously declared a device named dev012
able to be reconfigured to one of these three systems would be declared as follows (the connections of the instance, omitted in the example, can be done as usual):
sys0 :dev012 # dev012 is at first a standard instance of sys0
dev012.choice(conf1: sys1, conf2: sys2) # Now dev012 is reconfigurable
After the code above, instance dev012
can be dynamically reconfigured to sys0
, sys1
, and sys2
with respective names dev012
, conf1
, and conf2
.
Note: The name of the initial system in the reconfigurations is set to be the name of the instance.
A reconfigurable instance can then be reconfigured using the command configure
as follows:
<<span class="pl-en">instance</span>><span class="pl-kos">.</span><span class="pl-en">configure</span><span class="pl-kos">(</span><<span class="pl-en">name</span> <span class="pl-k">or</span> <span class="pl-en">index</span>><span class="pl-kos">)</span>
In the code above, the argument of configure
can either be the name of the configuration as previously declared with choice
, or its index in order of declaration. For example in the following code, instance dev012
is reconfigured to system sys1
, then system sys0
the system sys2
:
dev012.configure(:conf1)
!1000.ns
dev012.configure(:dev012)
!1000.ns
dev012.configure(2)
These reconfiguration commands are treated as regular RTL statements in HDLRuby and are supported by the simulator. However, in the current version of the HDLRuby, these statements are ignored when generating Verilog HDL or VHDL code.
Events
Each behavior of a system is associated with a list of events, called a sensitivity list, that specifies when the behavior is to be executed. An event is associated with a signal and represents the instant when the signal reaches a given state.
There are three kinds of events: positive edge events represent the instants when their corresponding signals vary from 0 to 1, and negative edge events
represent the instants when their corresponding signals vary from 1 to 0 and the change events represent the instants when their corresponding signals vary.
Events are declared directly from the signals, using the posedge
operator for a positive edge, the negedge
operator for a negative edge, and the change
operator for change. For example, the following code declares 3 behaviors activated respectively on the positive edge, the negative edge, and any change of the clk
signal.
inner :clk
par(clk.posedge) do
...
end
par(clk.negedge) do
...
end
par(clk.change) do
...
end
Note:
- The
change
keyword can be omitted.
Statements
Statements are the basic elements of a behavioral description. They are regrouped in blocks that specify their execution mode (parallel or sequential). There are four kinds of statements: the transmit statement which computes expressions and sends the result to the target signals, the control statement that changes the execution flow of the behavior, the block statement (described earlier), and the inner signal declaration.
Note:
- There is a fifth type of statement, named the time statement, that will be discussed in section Time.
Transmit statement
A transmit statement is declared using the arrow operator <=
within a behavior. Its right value is the expression to compute and its left value is a reference to the target signals (or parts of signals), i.e., the signals (or parts of signals) that receive the computation result.
For example, the following code transmits the value 3
to signal s0
and the sum of the values of signals i0
and i1
to the first four bits of signal s1
:
s0 <= 3
s1[3..0] <= i0 + i1
The behavior of a transmit statement depends on the execution mode of the enclosing block:
- If the mode is parallel, the target signals are updated when all the statements of the current block are processed.
- If the mode is sequential, the target signals are updated immediately after the right value of the statement is computed.
Control statements
There are only two possible control statements: the hardware if hif
and the hardware case hcase
.
hif
The hif
construct is made of a condition and a block that is executed if and only if the condition is met. It is declared as follows, where the condition can be any expression:
hif <condition> do
<block contents>
end
hcase
The hcase
construct is made of an expression and a list of value-block pairs.
A block is executed when the corresponding value is equal to the value of the expression of the hcase
. This construct is declared as follows:
hcase <expression>
hwhen <value 0> do
<block contents 0>
end
hwhen <value 1> do
<block contents 1>
end
...
helse
It is possible to add a block that is executed when the condition of an hif
is not met, or when no case matches the expression of a hcase
, using the helse
keyword as follows:
<hif or hcase construct>
helse do
<block contents>
end
helsif
In addition to helse
, it is possible to set additional conditions to an hif
using the helsif
keyword as follows:
hif <condition 0> do
<block contents 0>
end
helsif <condition 1> do
<block contents 1>
end
...
About loops
HDLRuby does not include any hardware construct for describing loops. This might look poor compared to the other HDL, but it is important to understand
that the current synthesis tools do not really synthesize hardware from such loops but instead preprocess them (e.g., unroll them) to synthesizable loop less hardware. In HDLRuby, such features are natively supported by the Ruby loop constructs (for
, while
, and so on), but also by advanced Ruby constructs like the enumerators (each
, times
, and so on).
Notes:
-
HDLRuby being based on Ruby, it is highly recommended to avoid
for
orwhile
constructs and to use enumerators instead. -
The Ruby
if
andcase
statements can also be used, but they do not represent any hardware. They are executed when the corresponding system is instantiated. For example, the following code will displayHello world!
when the described system is instantiated, provided the generic parameterparam
is not nil.system :say_hello do |param = nil| if param != nil then puts "Hello world!" end end
Types
Each signal and each expression is associated with a data type that describes the kind of value it can represent. In HDLRuby, the data types represent bit-vectors associated with the way they should be interpreted, i.e., as bit strings, unsigned values, signed values, or hierarchical contents.
Type construction
There are five basic types, bit
, signed
, unsigned
, integer
, and float
that represent respectively single bit logical values, single-bit unsigned values, single-bit signed values, Ruby integer values, and Ruby floating-point values (double precision). The first three types are HW and support four-valued logic, whereas the two last ones are SW (but are compatible with HW) and only support Boolean logic. Ruby integers can represent any element of Z (the mathematical integers) and have for that purpose a variable bit-width.
The other types are built from them using a combination of the two following type operators.
The vector operator []
is used for building types representing vectors of single or multiple other types. A vector whose elements have all the same type is declared as follows:
<<span class="pl-en">type</span>><span class="pl-kos">[</span><<span class="pl-en">range</span>><span class="pl-c1"></span><span class="pl-kos">]</span>
The <range>
of a vector type indicates the position of the starting and ending bits.
An n..0
range can also be abbreviated to n+1
. For instance, the two following types are identical:
bit[7..0]
bit[8]
A vector of multiple types, also called a tuple, is declared as follows:
[<type 0>, <type 1>, ... ]
For example, the following code declares the type of the vectors made of an 8-bit logical, a 16-bit signed, and a 16-bit unsigned values:
[ bit[8], signed[16], unsigned[16] ]
The structure operator {}
is used for building hierarchical types made of named subtypes. This operator is used as follows:
{ <name 0>: <type 0>, <name 1>: <type 1>, ... }
For instance, the following code declares a hierarchical type with an 8-bit subtype named header
and a 24-bit subtype named data
:
{ header: bit[7..0], data: bit[23..0] }
Type definition
It is possible to give names to type constructs using the typedef
keywords as follows:
<<span class="pl-en">type</span> <span class="pl-en">construct</span>><span class="pl-kos">.</span><span class="pl-en">typedef</span> <span class="pl-pds">:<name</span>>
For example, the following gives the name char
to a signed 8-bit vector:
signed[7..0].typedef :char
After this statement, char
can be used like any other type. For example, the following code sample declares a new input signal sig
whose type is char
:
char.input :sig
Alternatively, a new type can also be defined using the following syntax:
typedef : name> do
<code>
end
Where:
-
type name
is the name of the type -
code
is a description of the content of the type
For example, the previous char
could have been declared as follows:
typedef :char do
signed[7..0]
end
Type compatibility and conversion
The basis of all the types in HDLRuby is the vector of bits (bit vector) where each bit can have four values: 0, 1, Z, and X (for undefined). Bit vectors are by default unsigned but can be set to be signed. When performing computations between signals of different bit-vector types, the shorter signal is extended to the size of the larger one preserving its sign if it is signed.
While the underlying structure of any HDLRuby type is the bit vector, complex types can be defined. When using such types in computational expressions and assignments they are first implicitly converted to an unsigned bit vector of the same size.
Expressions
Expressions are any construct that represents a value associated with a type. They include immediate values, reference to signals and operations among other expressions using expression operators.
Immediate values
The immediate values of HDLRuby can represent vectors of bit
, unsigned
, and signed
, and integer or floating-point numbers. They are prefixed by a _
character and include a header that indicates the vector type and the base used for representing the value, followed by a numeral representing the value. The bit width of a value is obtained by default from the width of the numeral, but it is also possible to specify it in the header. In addition, the character _
can be put anywhere in the number for increasing the readability, it will be ignored.
The vector type specifiers are the followings:
-
b
:bit
type, can be omitted, -
u
:unsigned
type, (equivalent tob
and can be used for avoiding confusion with the binary specifier), -
s
:signed
type, the last figure is sign-extended if required by the binary, octal, and hexadecimal bases, but not for the decimal base.
The base specifiers are the followings:
-
b
: binary, -
o
: octal, -
d
: decimal, -
h
: hexadecimal.
For example, all the following immediate values represent an 8-bit hundred
(either in unsigned or signed representation):
_bb01100100
_b8b110_0100
_b01100100
_u8d100
_s8d100
_uh64
_s8o144
Finally, it is possible to omit either the type specifier, the default being unsigned bit, or the base specifier, the default being binary. For example, all the following immediate values represent an 8-bit unsigned hundred
:
_b01100100
_h64
_o144
Notes:
-
_01100100
used to be considered as equivalent to_b01100100
, however due to compatibility troubles with recent version of Ruby it is considered deprecated. -
Ruby immediate values can also be used, their bit width is automatically adjusted to match the data type of the expression they are used in. Please notice this adjusting may change the value of the immediate, for example, the following code will set
sig
to 4 instead of 100:[3..0].inner :sig sig <= 100
References
References are expressions used to designate signals or a part of signals.
The simplest reference is simply the name of a signal. It designates the signal corresponding to this name in the current scope. For instance, in the
following code, inner signal sig0
is declared, and therefore the name sig0 becomes a reference to designate this signal.
# Declaration of signal sig0.
inner :sig0
# Access to signal sig0 using a name reference.
sig0 <= 0
For designating a signal of another system, or a sub-signal in a hierarchical signal, you can use the .
operator as follows:
<<span class="pl-en">parent</span> <span class="pl-en">name</span>><span class="pl-kos">.</span><<span class="pl-en">signal</span> <span class="pl-en">name</span>>
For example, in the following code, input signal d
of system instance dff0
is connected to sub-signal sub0
of hierarchical signal sig
.
system :dff do
input :clk, :rst, :d
output :q
par(clk.posedge) { q <= d & ~rst }
end
system :my_system do
input :clk, :rst
{ sub0: bit, sub1: bit}.inner :sig
dff(:dff0).(clk: clk, rst: rst)
dff0.d <= sig.sub0
...
end
Expression operators
The following table gives a summary of the operators available in HDLRuby. More details are given for each group of operators in the subsequent sections.
Assignment operators (left-most operator of a statement):
symbol | description |
---|---|
:<= | connection, if outside behavior |
:<= | transmission, if inside behavior |
Arithmetic operators:
symbol | description |
---|---|
:+ | addition |
:- | subtraction |
:* | multiplication |
:/ | division |
:% | modulo |
:** | power |
:+@ | positive sign |
:-@ | negation |
Comparison operators:
symbol | description |
---|---|
:== | equality |
:!= | difference |
:> | greater than |
:< | smaller than |
:>= | greater or equal |
:<= | smaller or equal |
Logic and shift operators:
symbol | description |
---|---|
:& | bitwise / logical and |
: | |
:~ | bitwise / logical not |
:mux | multiplex |
:<< / :ls | left shift |
:>> / :rs | right shift |
:lr | left rotate |
:rr | right rotate |
Conversion operators:
symbol | description |
---|---|
:to_bit | cast to bit vector |
:to_unsigned | cast to unsigned vector |
:to_signed | cast to signed vector |
:to_big | cast to big endian |
:to_little | cast to little endian |
:reverse | reverse the bit order |
:ljust | increase width from the left, preserves the sign |
:rjust | increase width from the right, preserves the sign |
:zext | zero extension, converts to unsigned if signed |
:sext | sign extension, converts to sign |
Selection /concatenation operators:
symbol | description |
---|---|
:[] | sub vector selection |
:@[] | concatenation operator |
:. | field selection |
Notes:
-
The operator precedence is the one of Ruby.
-
Ruby does not allow to override the
&&
, the||
and the?:
operators so that they are not present in HDLRuby. Instead of the?:
operator, HDLRuby provides the more general multiplex operatormux
. However, HDLRuby does not provide any replacement for the&&
and the||
operators, please refer to section Logic operators for a justification about this issue.
Assignment operators
The assignment operators can be used with any type. They are the connection and the transmission operators both being represented by <=
.
Note:
- The first operator of a statement is necessarily an assignment operator, while the other occurrences of
<=
represent the usualless than or equal to
operators.
Arithmetic operators
The arithmetic operators can only be used on vectors of bit
, unsigned
or signed
values, integer
or float
values. These operators are +
, -
, *
, %
and the unary arithmetic operators are -
and +
. They have the same meaning as their Ruby equivalents.
Comparison operators
Comparison operators are the operators whose result is either true or false.
In HDLRuby, true and false are represented by respectively bit
value 1 and bit
value 0. These operators are ==
, !=
, <
, >
, <=
, >=
. They
have the same meaning as their Ruby equivalents.
Notes:
-
The
<
,>
,<=
and>=
operators can only be used on vectors ofbit
,unsigned
orsigned
values,integer
orfloat
values. -
When compared, values of a type different from the vector of
signed
and fromfloat
are considered as vectors ofunsigned
.
Logic and shift operators
In HDLRuby, the logic operators are all bitwise. For performing Boolean computations, it is necessary to use single-bit values. The bitwise logic binary operators are &
, |
, and ^
, and the unary one is ~
. They have the same meaning as their Ruby equivalents.
Note: there are two reasons why there are no Boolean operators
-
Ruby language does not support the redefinition of the Boolean operators
-
In Ruby, each value that is not
false
nornil
is assumed to be true. This is perfectly relevant for software, but not for hardware where the basic data types are bit vectors. Hence, it seemed preferable to support Boolean computation for one-bit values only, which can be done through bitwise operations.
The shift operators are <<
and >>
and have the same meaning as their Ruby equivalent. They do not change the bit width and preserve the sign for signed
values.
The rotation operators are rl
and rr
for respectively left and right bit rotations. Like the shifts, they do not change the bit width and preserve the sign for the signed
values. However, since such operators do not exist in Ruby, they are used like methods as follows:
<<span class="pl-en">expression</span>><span class="pl-kos">.</span><span class="pl-en">rl</span><span class="pl-kos">(</span><<span class="pl-en">other</span> <span class="pl-en">expression</span>><span class="pl-kos">)</span>
<<span class="pl-en">expression</span>><span class="pl-kos">.</span><span class="pl-en">rr</span><span class="pl-kos">(</span><<span class="pl-en">other</span> <span class="pl-en">expression</span>><span class="pl-kos">)</span>
For example, for rotating the left signal sig
3 times, the following code can be used:
sig.rl(3)
It is possible to perform other kinds of shifts or rotations using the selection and the concatenation operators. Please refer to section Concatenation and selection operators for more details about these operators.
Conversion operators
The conversion operators are used to change the type of an expression. There are two kinds of such operators: the type pun that does not change the raw value of the expression and the type cast that changes the raw value.
The type puns include to_bit
, to_unsigned
and to_signed
that convert expressions of any type type to vectors of respectively bit
, unsigned
and signed
elements. For example, the following code converts an expression of hierarchical type to an 8-bit signed vector:
[ up: signed[3..0], down: unsigned[3..0] ].inner :sig
sig.to_bit <= _b01010011
The type casts change both the type and the value and are used to adjust the width of the types. They can only be applied to vectors of bit
, signed
, or unsinged
and can only increase the bit width (bit width can be truncated using the selection operator, please refer to the next section).
These operators comprise the bit width conversions: ljust
, rjust
, zext
and sext
.
More precisely, the bit width conversions operate as follows:
-
ljust
andrjust
increase the size from respectively the left or the right side of the bit vector. They take as an argument the width of the new type and the value (0 or 1) of the bits to add. For example, the following code increases the size ofsig0
to 12 bits by adding 1 on the right:[7..0].inner :sig0 [11..0].inner :sig1 sig0 <= 25 sig1 <= sig0.ljust(12,1)
-
zext
increases the size by adding several 0 bits on the most significant bit side, this side depending on the endianness of the expression. This conversion takes as an argument the width of the resulting type. For example, the following code increases the size ofsig0
to 12 bits by adding 0 on the left:signed[7..0].inner :sig0 [11..0].inner :sig1 sig0 <= -120 sig1 <= sig0.zext(12)
-
sext
increases the size by duplicating the most significant bit, the side of the extension depending on the endianness of the expression. This conversion takes as an argument the width of the resulting type. For example, the following code increases the size ofsig0
to 12 bits by adding 1 on the right:signed[0..7].inner :sig0 [0..11].inner :sig1 sig0 <= -120 sig1 <= sig0.sext(12)
Concatenation and selection operators
Concatenation and selection are done using the []
operator as follows:
-
when this operator takes as arguments several expressions, it concatenates them. For example, the following code concatenates
sig0
tosig1
:[3..0].inner :sig0 [7..0].inner :sig1 [11..0].inner :sig2 sig0 <= 5 sig1 <= 6 sig2 <= [sig0, sig1]
-
when this operator is applied to an expression of
bit
,unsigned
orsigned
vector type while taking as argument a range, it selects the bits corresponding to this range. If only one bit is to select, the offset of this bit can be used instead. For example, the following code selects bits from 3 to 1 ofsig0
and bit 4 ofsig1
:[7..0].inner :sig0 [7..0].inner :sig1 [3..0].inner :sig2 bit.inner :sig3 sig0 <= 5 sig1 <= 6 sig2 <= sig0[3..1] sig3 <= sig1[4]
Implicit conversions
When there is no ambiguity, HDLRuby will automatically insert conversion operators when two types are not compatible with one another. The cases where such implicit conversions are applied are summarized in the following tables where:
-
operator
is the operator in use -
result width
is the width of the result's type -
result base
is the base type of the result's type -
S
is the shortest operand -
L
is the longest operand -
S operand type
is the base type of the shortest operand -
L operand type
is the base type of the longest operand -
operand conversion
is the conversions added to make the operands compatible. -
w
is the width of the operands after conversion -
lw
is the width of the left operand's type before conversion -
rw
is the width of the right operand's type before conversion
Additive and logical operators:
operator | result's width |
---|---|
<= (assign) | w (error is raised if L.width < R.width) |
+, - | w+1 |
&, |, ^ | w |
== | 1 |
< | 1 |
> | 1 |
<= (comp.) | 1 |
>= | 1 |
S operand base | L operand base | result base | operand conversion |
---|---|---|---|
bit | bit | bit | S.zext(L.width) |
bit | unsigned | unsigned | S.zext(L.width).to_unsigned |
bit | signed | signed | S.zext(max(S.width+1,L.width).to_signed |
unsigned | bit | unsigned | S.zext(L.width), L.to_unsigned |
unsigned | unsigned | unsigned | S.zext(L.width) |
unsigned | signed | signed | S.zext(max(S.width+1,L.width).to_signed |
signed | bit | signed | S.sext(L.width+1), L.zext(L.width+1).to_signed |
signed | unsigned | signed | S.sext(L.width+1), L.zext(L.width+1).to_signed |
signed | signed | signed | S.sext(L.width) |
Multiplicative operators:
operator | result width |
---|---|
* | lw * rw |
/ | lw |
% | rw |
** | rw |
<< / ls | lw |
>> / rs | lw |
lr | lw |
rr | lw |
S operand base | L operand base | result base | operand conversion |
---|---|---|---|
bit | bit | bit | |
bit | unsigned | unsigned | S.to_unsigned |
bit | signed | signed | S.zext(S.width+1).to_signed |
unsigned | bit | unsigned | L.to_unsigned |
unsigned | unsigned | unsigned | |
unsigned | signed | signed | S.zext(S.width).to_signed |
signed | bit | signed | L.zext(L.width+1).to_signed |
signed | unsigned | signed | L.zext(L.width+1).to_signed |
signed | signed | signed |
Functions
HDLRuby functions
Like Verilog HDL, HDLRuby provides function constructs for reusing code. HDLRuby functions are declared as follows:
<span class="pl-en">function</span> <span class="pl-pds">:<function</span> <span class="pl-en">name</span>> <span class="pl-en">do</span> |<<span class="pl-en">arguments</span>>|
<<span class="pl-en">code</span>>
<span class="pl-en">end</span>
Where:
-
function name
is the name of the function. -
arguments
is the list of arguments of the function. -
code
is the code of the function.
Notes:
-
Functions have their scope, so any declaration within a function is local. It is also forbidden to declare interface signals (input, output, or inout) within a function.
-
Like the Ruby proc objects, the last statement of a function's code serves as the return value. For instance, the following function returns
1
(in this example the function does not have any argument):function :one { 1 }
-
Functions can accept any kind of object as an argument, including variadic arguments or blocks of code as shown below with a function that applies the code passed as an argument to all the variadic arguments of
args
:function :apply do |*args, &code| args.each { |arg| code.call(args) } end
Such a function can be used for example for connecting a signal to a set of other signals as follows (where
sig
is connected tox
,y
andz
):<span class="pl-en">apply</span><span class="pl-kos">(</span><span class="pl-en">x</span><span class="pl-kos">,</span><span class="pl-en">y</span><span class="pl-kos">,</span><span class="pl-en">z</span><span class="pl-kos">)</span> <span class="pl-kos">{</span> |<span class="pl-s1">v</span>| <span class="pl-s1">v</span> <= <span class="pl-en">sig</span> <span class="pl-kos">}</span>
A function can be invoked anywhere in the code using its name and passing its argument between parentheses as follows:
<<span class="pl-en">function</span> <span class="pl-en">name</span>><span class="pl-kos">(</span><<span class="pl-en">list</span> <span class="pl-en">of</span> <span class="pl-en">values</span>><span class="pl-c1"></span><span class="pl-kos">)</span>
Ruby functions
HDLRuby functions are useful for reusing code, but they cannot interact with the code they are called in. For example, it is not possible to add interface signals through a function nor to modify a control statement (e.g., hif
) with them. These high-level generic operations can however be performed using the functions of the Ruby language declared as follows:
def <function name>(<arguments>)
<code>
end
Where:
-
function name
is the name of the function. -
arguments
is the list of arguments of the function. -
code
is the code of the function.
These functions are called the same way HDLRuby functions are called, but this operation pastes the code of the function as is within the code. Moreover, these functions do not have any scope so any inner signal or instance declared within them will be added to the object they are invoked in.
For example, the following function will add input in0
to any system where it is invoked:
def add_in0
input :in0
end
This function can be used as follows:
system :sys do
...
add_in0
...
end
As another example, following function will add an alternative code that generates a reset to a condition statement (hif
or hcase
):
def too_bad
helse { $rst <= 1 }
end
This function can be used as follows:
system :sys do
...
par do
hif(sig == 1) do
...
end
too_bad
end
end
Ruby functions can be compared to the macros of the C languages: they are more flexible since they edit the code they are invoked in, but they are also dangerous to use. In general, it is not recommended to use them, unless when designing a library of generic code for HDLRuby.
Time
Time values
In HDLRuby, time values can be created using the time operators: s
for seconds, ms
for a millisecond, us
for microseconds, ns
for nanoseconds, ps
for picoseconds. For example, the followings are all indicating one second:
1.s
1000.ms
1000000.us
1000000000.ns
1000000000000.ps
Time behaviors and time statements
Like the other HDL, HDLRuby provides specific statements that model the advance of time. These statements are not synthesizable and are used for simulating the environment of a hardware component. For sake of clarity, such statements are only allowed in explicitly non-synthesizable behavior declared using the timed
keyword as follows.
timed do
<statements>
end
A time behavior does not have any sensitivity list, but it can include any statement supported by a standard behavior in addition to the time statements. There are two kinds of such statements:
-
The
wait
statements: such a statement blocks the execution of the behavior for the time given in the argument. For example, the following code waits for 10ns before proceeding:<span class="pl-en">wait</span><span class="pl-kos">(</span><span class="pl-c1">10</span><span class="pl-kos">.</span><span class="pl-en">ns</span><span class="pl-kos">)</span>
This statement can also be abbreviated using the
!
operator as follows:!<span class="pl-c1">10</span><span class="pl-kos">.</span><span class="pl-en">ns</span>
-
The
repeat
statements: such a statement takes as argument a number of iteration and a block. The execution of the block is repeated the given number times. For example, the following code executes 10 times the inversion of theclk
signal every 10 nanoseconds:<span class="pl-en">repeat</span><span class="pl-kos">(</span><span class="pl-c1">10</span><span class="pl-kos">)</span> <span class="pl-k">do</span> !<span class="pl-c1">10</span><span class="pl-kos">.</span><span class="pl-en">ns</span> <span class="pl-en">clk</span> <= ~<span class="pl-en">clk</span> <span class="pl-k">end</span>
Note:
This statement is not synthesizable and therefore can only be used in timed behaviors.
Parallel and sequential execution
Time behaviors are by default sequential, but they can include both parallel and sequential blocks. The execution semantic is the following:
-
A sequential block in a time behavior is executed sequentially.
-
A parallel block in a time behavior is executed in a semi-parallel fashion as follows:
-
Statements are grouped in sequence until a time statement is met.
-
The grouped sequence are executed in parallel.
-
The time statement is executed.
-
The subsequent statements are processed the same way.
-
High-level programming features
Using Ruby in HDLRuby
Since HDLRuby is pure Ruby code, the constructs of Ruby can be freely used without any compatibility issues. Moreover, this Ruby code will not interfere with the synthesizability of the design. It is then possible to define Ruby classes, methods, or modules whose execution generates constructs of HDLRuby.
Generic programming
Declaring
Declaring generic systems
Systems can be declared with generic parameters as follows:
system : name> do |<list of generic parameters>|
...
end
For example, the following code describes an empty system with two generic parameters named respectively a
and b
:
system(:nothing) { |a,b| }
The generic parameters can be anything: values, data types, signals, systems, Ruby variables, and so on. For example, the following system uses generic argument t
as a type for an input signal, generic argument w
as a bit range for an output signal, and generic argument s
as a system used for creating instance sI
whose input and output signals i
and o
are connected respectively to signals isig
and osig
.
system :something do |t,w,s|
t.input isig
[w].output osig
s :sI.(i: isig, o: osig)
end
It is also possible to use a variable number of generic parameters using the variadic operator *
like in the following example. In this example, args
is an array containing an indefinite number of parameters.
system(:variadic) { |*args| }
Declaring generic types
Data types can be declared with generic parameters as follows:
typedef : name> do |<list of generic parameters>|
...
end
For example, the following code describes a bit-vector type with generic number of bits width
:
type(:bitvec) { |width| bit[width] }
Like with the systems, the generic parameters of types can be any kind of object, and it is also possible to use variadic arguments.
Specializing
Specializing generic systems
A generic system is specialized by invoking its name and passing as an argument the values corresponding to the generic arguments as follows:
<<span class="pl-en">system</span> <span class="pl-en">name</span>><span class="pl-kos">(</span><<span class="pl-en">generic</span> <span class="pl-en">argument</span> <span class="pl-en">value</span>'<span class="pl-en">s</span> <span class="pl-en">list</span>><span class="pl-c1"></span><span class="pl-kos">)</span>
If fewer values are provided than the number of generic arguments, the system is partially specialized. However, only a fully specialized system can be instantiated.
A specialized system can also be used for inheritance. For example, assuming system sys
has 2 generic arguments, it can be specialized and used for building system subsys
as follows:
system :subsys, sys(1,2) do
...
end
This way of inheriting can only be done with fully specialized systems though. For partially specialized systems, include
must be used instead. For example, if sys
specialized with only one value, can be used in generic subsys_gen
as follows:
system :subsys_gen do |param|
include sys(1,param)
...
end
Note:
- In the example above, the generic parameter
param
ofsubsys_gen
is used for specializing systemsys
.
Specializing generic types
A generic type is specialized by invoking its name and passing as an argument the values corresponding to the generic arguments as follows:
<<span class="pl-en">type</span> <span class="pl-en">name</span>><span class="pl-kos">(</span><<span class="pl-en">generic</span> <span class="pl-en">argument</span> <span class="pl-en">value</span>'<span class="pl-en">s</span> <span class="pl-en">list</span>><span class="pl-c1"></span><span class="pl-kos">)</span>
If fewer values are provided than the number of generic arguments, the type is partially specialized. However, only a fully specialized type can be used for declaring signals.
Use of signals as generic parameters
Signals passed as generic arguments to systems can be used for making generic connections to the instance of the system. For that purpose, the generic argument has to be declared as input, output, or inout port in the body of the system as follows:
system :> do |sig|
sig.input :my_sig
...
end
In the code above, sig
is a generic argument assumed to be a signal. The second line declares the port to which sig will be connected to when instantiating. From there, port my_sig
can be used like any other port of the system. Such a system is then instantiated as follows:
system_name(some_sig) :>
In the code above, some_sig
is a signal available in the current context. This instantiation automatically connects some_sig
to the instance.
Inheritance
Basics
In HDLRuby, a system can inherit from the content of one or several other parent systems using the include
command as follows: include <list of systems>
. Such an include can be put anywhere in the body of a system, but the resulting content will be accessible only after this command.
For example, the following code describes first a simple D-FF, and then uses it to describe a FF with an additional reversed output (qb
):
system :dff do
input :clk, :rst, :d
output :q
par(clk.posedge) { q <= d & ~rst }
end
system :dff_full do
output :qb
include dff
qb <= ~q
end
It is also possible to declare inheritance in a more object-oriented fashion by listing the parents of a system just after declaring its name as follows:
system : system name>, <list of parent systems> do
<additional system code>
end
For example, the following code is another to describe dff_full
:
system :dff_full, dff do
output :qb
qb <= ~q
end
Note:
- As a matter of implementation, HDLRuby systems can be viewed as sets of methods used for accessing various constructs (signals, instances). Hence inheritance in HDLRuby is closer to the Ruby mixin mechanism than to a true software inheritance.
About inner signals and system instances
By default, inner signals and instances of a parent system are not accessible by its child systems. They can be made accessible using the export
keyword as follows: export <symbol 0>, <symbol 1>, ...
. For example, the following
code exports signals clk
and rst
and instance dff0
of system exporter
so that they can be accessed in child system importer
.
system :exporter do
input :d
inner :clk, :rst
dff(:dff0).(clk: clk, rst: rst, d: d)
export :clk, :rst, :dff0
end
system :importer, exporter do
input :clk0, :rst0
output :q
clk <= clk0
rst <= rst0
dff0.q <= q
end
Note:
-
export takes as arguments the symbols (or the strings) representing the name of the components to export and not a reference to them. For instance, the following code is invalid:
system :exporter do input :d inner :clk, :rst dff(:dff0).(clk: clk, rst: rst, d: d) export clk, rst, dff0 end
Conflicts when inheriting
Signals and instances cannot be overridden, this is also the case for signals and instances accessible through inheritance. For example, the following code is invalid since rst
has already been defined in dff
:
<span class="pl-en">system</span> <span class="pl-pds">:dff_bad</span><span class="pl-kos">,</span> <span class="pl-en">dff</span> <span class="pl-k">do</span>
<span class="pl-en">input</span> <span class="pl-pds">:rst</span>
<span class="pl-k">end</span>
Conflicts among several inherited systems can be avoided by renaming the signals and instances that collide with one another as shown in the next section.
Shadowed signals and instances
It is possible in HDLRuby to declare a signal or an instance whose name is identical to the one used in one of the included systems. In such a case, the corresponding construct of the included system is still present, but it is not directly accessible even if exported, they are said to be shadowed.
To access the shadowed signals or instances, a system must be reinterpreted as the relevant parent system using the as
operator as follows: as(system)
.
For example, in the following code signal, db
of system dff_db
is shadowed by signal db
of system dff_shadow
, but it is accessed using the as
operator.
system :dff_db do
input :clk,:rst,:d
inner :db
output :q
db <= ~d
(q <= d & ~rst).at(clk.posedge)
end
system :dff_shadow, dff_db do
output :qb, :db
db <= ~d
qb <= as(dff_db).db
end
Opening a system
It is possible to pursue the definition of a system after it has been declared using the open
methods as follows:
<system>.open do
<additional system description>
end
For example, dff
, a system describing a D-FF, can be modified to have an inverted output as follows:
dff.open do
output :qb
qb <= ~q
end
Opening an instance
When there is a modification to apply to an instance, it is sometimes preferable to modify this sole instance rather than declaring a new system to derivate the instance from. For that purpose, it is possible to open an instance for modification as follows:
<instance name>.open do
<additional description for the instance>
end
For example, an instance of the previous dff
system can be extended with an inverted output as follows:
system :some_system do
...
dff :dff0
dff0.open do
output :qb
qb <= ~q
end
...
end
Overloading of operators
Operators can be overloaded for specific types. This allows for instance to support seamlessly fixed-point computations without requiring explicit readjustment of the position of the decimal point.
An operator is redefined as follows:
<type>.define_operator(:>) do |<args>|
<operation description>
end
Where:
-
type
is the type from which the operation is overloaded. -
op
is the operator that is overloaded (e.g.,+
) -
args
are the arguments of the operation. -
operation description
is an HDLRuby expression of the new operation.
For example, for fix32
a 32-bit (decimal point at 16-bit) fixed-point type defined as follows:
signed[31..0].typedef(:fix32)
The multiplication operator can be overloaded as follows to ensure the decimal point have always the right position:
fix32.define_operator(:*) do |left,right|
(left.as(signed[31..0]) * right) >> 16
end
Please notice, that in the code above, the left value has been cast to a plain bit-vector to avoid the infinite recursive call of the *
operator.
Operators can also be overloaded with generic types. However, in such a case, the generic argument must also be present in the list of arguments of the overloaded operators. For instance, let us consider the following fixed-point type of variable width (and whose decimal point is set at the half of its bit range):
typedef(:fixed) do |width|
signed[(width-1)..0]
end
The multiplication operator would be overloaded as follows:
fixed.define_operator do |width,left,right|
(left.as(signed[(width-1)..0]) * right) >> width/2
end
Predicate and access methods
To get information about the current state of the hardware description HDLRuby provides the following predicates:
predicate name | predicate type | predicate meaning |
---|---|---|
is_block? |
bit | tells if in execution block |
is_par? |
bit | tells if current parallel block is parallel |
is_seq? |
bit | tells if current parallel block is sequential |
is_clocked? |
bit | tells if current behavior is clocked (activated on a sole rising or falling edge of a signal) |
cur_block |
block | gets the current block |
cur_behavior |
behavior | gets the current behavior |
cur_systemT |
system | gets the current system |
top_block |
block | gets the top block of the current behavior |
one_up |
block/system | gets the upper construct (block or system) |
last_one |
any | last declared construct |
Several enumerators are also provided for accessing the internals of the current construct (in the current state):
enumerator name | accessed elements |
---|---|
each_input |
input signals of the current system |
each_output |
output signals of the current system |
each_inout |
inout signals of the current system |
each_behavior |
behaviors of the current system |
each_event |
events of the current behavior |
each_block |
blocks of the current behavior |
each_statement |
statements of the current block |
each_inner |
inner signals of the current block (or system if not within a block) |
Global signals
HDLRuby allows to declare global signals the same way system's signals are declared, but outside the scope of any system. After being declared, these signals are accessible directly from within any hardware construct.
To ease the design of standardized libraries, the following global signals are defined by default:
signal name | signal type | signal function |
---|---|---|
$reset |
bit | global reset |
$resetb |
bit | global reset complement |
$clk |
bit | global clock |
Note:
- When not used, the global signals are discarded.
Defining and executing Ruby methods within HDLRuby constructs
Like with any Ruby program it is possible to define and execute methods anywhere in HDLRuby using the standard Ruby syntax. When defined, a method is attached to the enclosing HDLRuby construct. For instance, when defining a method when declaring a system, it can be used within this system only, while when defining a method outside any construct, it can be used everywhere in the HDLRuby description.
A method can include HDLRuby code in which case the resulting hardware is appended to the current construct. For example, the following code adds a connection between sig0
and sig1
in system sys0
, and transmission between sig0
and sig1
in the behavior of sys1
.
def some_arrow
sig1 <= sig0
end
system :sys0 do
input :sig0
output :sig1
some_arrow
end
system :sys1 do
input :sig0, :clk
output :sig1
par(clk.posedge) do
some_arrow
end
end
Warning:
-
In the above example, the semantic of
some_arrow
changes depending on where it is invoked from, e.g., within a system, it is a connection, within a behavior, it is a transmission. -
Using Ruby methods for describing hardware might lead to weak code, for example, in the following code, the method declares
in0
as an input signal. Hence, while used insys0
no problem happens, an exception will be raised forsys1
because a signalin0
is already declared and will also be raised forsys2
because it is not possible to declare an input from within a behavior.def in_decl input :in0 end system :sys0 do in_decl end system :sys1 do input :in0 in_decl end system :sys2 do par do in_decl end end
Like any other Ruby method, methods defined in HDLRuby support variadic arguments named arguments, and block arguments. For example, the following method can be used to connect a driver to multiple signals:
def mconnect(driver, *signals)
signals.each do |signal|
signal <= driver
end
end
system :sys0 do
input :i0
input :o0, :o1, :o2, :o3
mconnect(i0,o0,o1,o2,o3)
end
While requiring care, properly designed method can be very useful for clean code reuse. For example, the following method allows to start the execution of a block after a given number of cycles:
def after(cycles,rst = $rst, &code)
sub do
inner :count
hif rst == 1 do
count <= 0
end
helse do
hif count < cycles do
count <= count + 1
end
helse do
instance_eval(&code)
end
end
end
end
In the code above:
-
the default initialization of
rst
to$rst
allows resetting the counter even if no such signal is provided as an argument. -
sub
ensures that thecount
signal does not conflict with another signal with the same name. -
the
instance_eval
keyword is a standard Ruby method that executes the block passed as an argument in context.
The following is an example that switches a LED on after 1000000 clock cycles using the previously defined after
ruby method:
system :led_after do
output :led
input :clk
par(clk.posedge) do
(led <= 0).hif($rst)
after(100000) { led <= 1 }
end
end
Note:
- Ruby's closure still applies in HDLRuby, hence, the block sent to
after
can use the signals and instances of the current block. Moreover, the signal declared in this method will not collide with them.
Dynamic description
When describing a system, it is possible to disconnect or completely undefine a signal or an instance.
Extending HDLRuby
Like any Ruby classes, the constructs of HDLRuby can be dynamically extended. If it is not recommended to change their internal structure, it is possible to add methods to them for an extension.
Extending HDLRuby constructs globally
By global extension of hardware constructs, we mean the classical extension of Ruby classes by monkey patching the corresponding class. For example, it is possible to add a method giving the number of signals in the interface of a system instance as follows:
class SystemI
def interface_size
return each_input.size + each_output.size + each_inout.size
end
end
From there, the method interface_size
can be used on any system instance as follows: <system instance>.interface_size
.
The following table gives the class of each construct of HDLRuby.
construct | class |
---|---|
data type | Type |
system | SystemT |
scope | Scope |
system instance | SystemI |
signal | Signal |
connection | Connection |
par/seq | Behavior |
timed | TimeBehavior |
event | Event |
par/seq/sub | Block |
transmit | Transmit |
hif | If |
hcase | Case |
Extending HDLRuby constructs locally
By local extension of a hardware construct, we mean that while the construct will be changed, all the other constructs will remain unchanged. This is achieved like in Ruby by accessing the Eigen class using the singleton_class
method and extending it using the class_eval
method. For example, with the following code, only system dff
will respond to method interface_size
:
dff.singleton_class.class_eval do
def interface_size
return each_input.size + each_output.size + each_inout.size
end
end
It is also possible to extend locally an instance using the same methods.
For example, with the following code, only instance dff0
will respond to method interface_size
:
dff :dff0
dff0.singleton_class.class_eval do
def interface_size
return each_input.size + each_output.size + each_inout.size
end
end
Finally, it is possible to extend locally all the instances of a system using method singleton_instance
in place of method singleton_class
.
For example, with the following code, all the instances of system dff
will respond to method interface_size
:
dff.singleton_instance.class_eval do
def interface_size
return each_input.size + each_output.size + each_inout.size
end
end
Modifying the generation behavior
The main purpose of allowing global and local extensions for hardware constructs is to give the user the possibility to implement its synthesis methods. For example, one may want to implement some algorithm for a given kind of system. For that purpose, the user can define an abstract system (without any hardware content), that holds the specific algorithm as follows:
system(:my_base) {}
my_base.singleton_instance.class_eval do
def my_generation
<some code>
end
end
Then, when this system named my_base
is included in another system, this latter will inherit from the algorithms implemented inside method my_generation
as shown in the following code:
system :some_system, my_base do
<some system description>
end
However, when generation the low-level description of this system, code like the following will have to be written for applying my_generation
:
some_system :instance0
instance0.my_generation
low = instance0.to_low
This can be avoided by redefining the to_low
method as follows:
system(:my_base) {}
my_base.singleton_instance.class_eval do
def my_generation
<some code>
end
alias :_to_low :to_low
def to_low
my_generation
_to_low
end
end
This way, calling directly to_low
will automatically use my_generation
.
Standard library
The standard libraries are included in the module Std
.
They can be loaded as follows, where <library name>
is the name of the
library:
require 'std/'
After the libraries are loaded, the module Std
must be included as follows:
include HDLRuby::High::Std
However,
hdrcc
does load the stable components of the standard library by default, so that you do not need to require nor include anything more to use them. In the current version, the stable components are the followings:
-
std/clocks.rb
-
std/fixpoint.rb
-
std/decoder.rb
-
std/fsm.rb
-
std/sequencer.rb
-
std/sequencer_sync.rb
std/clocks.rb
Clocks:
The clocks
library provides utilities for easier handling of clock synchronizations.
It adds the possibility to multiply events by an integer. The result is a new event whose frequency is divided by the integer multiplicand. For example, the following code describes a D-FF that memorizes each three clock cycles.
require 'std/clocks'
include HDLRuby::High::Std
system :dff_slow do
input :clk, :rst
input :d
output :q
( q <= d & ~rst ).at(clk.posedge * 3)
end
Note: this library does generate all the RTL code for the circuit handling the division of the frequency.
std/counters.rb
Counters:
This library provides two new constructs for implementing synthesizable wait statements.
The first construct is the after
statement that activates a block after a given number of clock cycles is passed. Its syntax is the following:
after(<number>,<clock>,<reset>)
Where:
-
<number>
is the number of cycles to wait. -
<clock>
is the clock to use, this argument can be omitted. -
<reset>
is the signal used to reset the counter used for waiting, this argument can be omitted.
This statement can be used either inside or outside a clocked behavior. When used within a clocked behavior, the clock event of the behavior is used for the counter unless specified otherwise. When used outside such behavior, the clock is the global default clock $clk
. In both cases, the reset is the global reset $rst
unless specified otherwise.
The second construct is the before
statement that activates a block until a given number of clock cycles is passed. Its syntax and usage are identical to the after
statement.
std/decoder.rb
Decoder:
This library provides a new set of control statements for easily describing an instruction decoder.
A decoder can be declared anywhere in the code describing a system using the decoder
keyword as follows:
decoder(<signal>) <block>
Where signal
is the signal to decode and block
is a procedure block (i.e., Ruby proc
) describing the decoding procedure. This procedure block can contain any code supported by a standard behavior, but also supports the entry
statement that describes a pattern of a bit vector to decode and the corresponding action to perform when the signal matches this pattern. The syntax of the entry
statement is the following:
entry(<pattern>) <block>
Where pattern
is a string describing the pattern to match the entry, and block
is a procedure block describing the actions (some HDLRuby code) that are performed when the entry matches. The string describing the pattern can include 0
and 1
characters for specifying a specific value for the corresponding bit, or any alphabetical character for specifying a field in the pattern. The fields in the pattern can then be used by name in the block describing the action. When a letter is used several times within a pattern, the corresponding bits are concatenated and are used as a signal multi-bit signal in the block.
For example, the following code describes a decoder for signal ir
with two entries, the first one computing the sum of fields x
and y
and assigning the result to signal s
and the second one computing the sum of fields x
y
and z
and assigning the result to signal s
:
decoder(ir) do
entry("000xx0yy") { s <= x + y }
entry("10zxxzyy") { s <= x + y + z }
end
It can be noticed for field z
in the example above that the bits are not required to be contiguous.
std/fsm.rb
FSM:
This library provides a new set of control statements for easily describing a finite state machine (FSM).
A finite state machine can be declared anywhere in a system provided it is outside a behavior using the fsm
keyword as follows:
fsm(<event>,<reset>,<mode>) <block>
Where event
is the event (rising or falling edge of a signal) activating the state transitions, rst
is the reset signal, and mode
is the default execution mode and block
is the execution block describing the states of the FSM. This last parameter can be either :sync
for synchronous (Moore type) or :async
for asynchronous (Mealy type).
The states of an FSM are described as follows:
<<span class="pl-en">kind</span>><span class="pl-kos">(</span><<span class="pl-en">name</span>><span class="pl-en"></span><span class="pl-kos">)</span> <<span class="pl-en">block</span>><span class="pl-en"></span>
Where kind
is the kind of state, name
is the name of the state, and block
is the actions to execute for the corresponding state. The kinds of states are the followings:
- reset: the state reached when resetting the FSM. This state can be forced to be asynchronous by setting the
name
argument to:async
and forced to be synchronous by setting thename
argument to:sync
. By default, thename
argument is to be omitted. - state: the default kind of state, it will be synchronous if the FSM is synchronous or asynchronous otherwise.
- sync: the synchronous kind of state, it will be synchronous whatever the kind of FSM is used.
- async: the asynchronous kind of state, it will be asynchronous whatever the kind of FSM is used.
In addition, it is possible to define a default action that will be executed whatever the state is using the following statement:
default <block>
Where block
is the action to execute.
State transitions are by default set to be from one state to the following in the description order. If no more transition is declared the next one is the first declared transition. A specific transition is defined using the goto
statement as the last statement of the action block as follows:
goto(<condition>,<names>)
Where condition
is a signal whose value is used as an index for selecting the target state among the ones specified in the names
list. For example, the following statement indicates to go to the state named st_a
if the cond
is 0, st_b
if the condition is 1, and st_c
if the condition is 2, otherwise this specific transition is ignored:
goto(cond,:st_a,:st_b,:st_c)
Several goto statements can be used, the last one having priority provided it is taken (i.e., its condition corresponds to one of the target states). If no goto is taken, the next transition is the next declared one.
For example, the following code describes an FSM describing a circuit that checks if two buttons (but_a
and but_b
) are pressed and released in sequence for activating an output signal (ok
):
fsm(clk.posedge,rst,:sync) do
default { ok <= 0 }
reset do
goto(but_a, :reset, but_a_on)
end
state(:but_a_on) do
goto(but_a, :but_a_off, :but_a_on)
end
state(:but_a_off) do
goto(but_b, :but_a_off, :but_b_on)
end
state(:but_b_on) do
goto(but_b, :but_b_off, :but_b_on)
end
state(:but_b_off) do
ok <= 1
goto(:but_b_off)
end
end
Note: the goto statements act globally, i.e., they are independent of the place where they are declared within the state. For example for both following statements, the next state will always be st_a
whatever cond
maybe:
<span class="pl-en">state</span><span class="pl-kos">(</span><span class="pl-pds">:st_0</span><span class="pl-kos">)</span> <span class="pl-k">do</span>
<span class="pl-en">goto</span><span class="pl-kos">(</span><span class="pl-pds">:st_a</span><span class="pl-kos">)</span>
<span class="pl-k">end</span>
<span class="pl-en">state</span><span class="pl-kos">(</span><span class="pl-pds">:st_1</span><span class="pl-kos">)</span> <span class="pl-k">do</span>
<span class="pl-en">hif</span><span class="pl-kos">(</span><span class="pl-en">cond</span><span class="pl-kos">)</span> <span class="pl-kos">{</span> <span class="pl-en">goto</span><span class="pl-kos">(</span><span class="pl-pds">:st_a</span><span class="pl-kos">)</span> <span class="pl-kos">}</span>
<span class="pl-k">end</span>
That is to say, for a conditional goto
for st_1
the code should have been written as follows:
<span class="pl-en">state</span><span class="pl-kos">(</span><span class="pl-pds">:st_1</span><span class="pl-kos">)</span> <span class="pl-k">do</span>
<span class="pl-en">goto</span><span class="pl-kos">(</span><span class="pl-en">cond</span><span class="pl-kos">,</span><span class="pl-pds">:st_a</span><span class="pl-kos">)</span>
<span class="pl-k">end</span>
The use of goto
makes the design of FSM shorter for a majority of the cases, be sometimes, a finer control is required. For that purpose, it is also possible to configure the FSM is static
mode where the next_state
statement that indicates implicitly the next state. Putting in static mode is done by passing :static
as an argument when declaring the FSM. For example, the following FSM uses next_state
to specify explicitly the next states depending on some condition signals cond0
and cond1
:
fsm(clk.posedge,rst,:static)
state(:st_0) do
next_state(:st_1)
state(:st_1) do
hif(cond) { next_state(:st_1) }
helse { next_state(:st_0) }
end
end
std/sequencer.rb
Sequencer (software-like hardware coding)::
This library provides a new set of control statements for describing the behavior of a circuit. Behind the curtain, these constructs build a finite state machine where states are deduced from the control points within the description.
A sequencer can be declared anywhere in a system provided it is outside a behavior using the sequencer
keyword as follows:
sequencer(<clock>,<start>) <block>
Where clock
is the clock signal advancing the execution of the sequence, start
is the signal starting the execution, and block
is the description of the sequence to be executed. Both clock
and start
can also be events (i.e., posedge
or negedge
).
A sequence is a specific case of a seq
block that includes the following software-like additional constructs:
-
step
: wait until the next event (given argumentevent
of the sequencer). -
sif(<condition>) <block>
: executesblock
ifcondition
is met. -
selsif(<condition>) <block>
: executesblock
if previoussif
orselsif
condition is not met and if currentcondition
is met. -
selse <block>
: executesblock
if the condition of the previoussif
statement is not met. -
swait(<condition>)
: waits until thatcondition
is met. -
swhile(<condition>) <block>
: executesblock
whilecondition
is met. -
sfor(<enumerable>) <block>
: executesblock
on each element ofenumerable
. This latter can be any enumerable Ruby object or any signal. If the signal is not hierarchical (e.g., bit vector), the iteration will be over each bit. -
sbreak
: ends current iteration. -
scontinue
: goes to the next step of the iteration. -
sterminate
: ends the execution of the sequence.
It is also possible to use enumerators (iterators) similar to the Ruby each
using the following methods within sequences:
-
<object>.seach
:object
any enumerable Ruby object or any signal. If a block is given, it works likesfor
, otherwise, it returns a HDLRuby enumerator (please see enumerator for details about them). -
<object>.stimes
: can be used on integers and is equivalent toseach
on each integer from 0 up toobject-1
. -
<object>.supto(<last>)
: can be used on integers and is equivalent toseach
on each integer fromobject
up tolast
. -
<object>.sdownto(<last>)
: can be used on an integer and is equivalent toseach
on each integer fromobject
down tolast
.
The objects that support these methods are called enumerable objects. They include the HDLRuby signals, the HDLRuby enumerators, and all the Ruby enumerable objects (e.g., ranges, arrays).
Here are a few examples of sequencers synchronized in the positive edge of clk
and starting when start
becomes one. The first one computes the Fibonacci series until 100, producing a new term in signal v
at each cycle:
require 'std/sequencer.rb'
include HDLRuby::High::Std
system :a_circuit do
inner :clk, :start
[16].inner :a, :b
sequencer(clk.posedge,start) do
a <= 0
b <= 1
swhile(v < 100) do
b <= a + b
a <= b - a
end
end
end
The second one computes the square of the integers from 10 to 100, producing one result per cycle in signal a
:
inner :clk, :start
[16].inner :a
sequencer(clk.posedge,start) do
10.supto(100) { |i| a <= i*i }
end
The third one reverses the content of memory mem
(the result will be "!dlrow olleH"):
inner :clk, :start
bit[8][-12].inner mem: "Hello world!"
sequencer(clk.posedge,start) do
mem.size.stimes do |i|
[8].inner :tmp
tmp <= mem[i]
mem[i] <= mem[-i-1]
mem[-i-1] <= tmp
end
end
The fourth one computes the sum of all the elements of memory mem
but stops if the sum is larger than 16:
inner :clk, :start
bit[8][-8].inner mem: [ _h02, _h04, _h06, _h08, _h0A, _h0C, _h0E ]
bit[8] :sum
sequencer(clk.posedge,start) do
sum <= 0
sfor(mem) do |elem|
sum <= sum + elem
sif(sum > 16) { sterminate }
end
end
std/sequencer.rb
HDLRuby enumerators and enumerable objects: HDLRuby enumerators are objects for generating iterations within sequencers. They are created using the method seach
on enumerable objects as presented in the previous section.
The enumerators can be controlled using the following methods:
-
size
: returns the number of elements the enumerator can access. -
type
: returns the type of the elements accessed by the enumerator. -
seach
: returns the current enumerator. If a block is given, performs the iteration instead of returning an enumerator. -
seach_with_index
: returns an enumerator over the elements of the current enumerator associated with their index position. If a block is given, performs the iteration instead of returning an enumerator. -
seach_with_object(<obj>)
: returns an enumerator over the elements of the current enumerator associated with objectobj
(any object, HDLRuby or not, can be used). If a block is given, performs the iteration instead of returning an enumerator. -
with_index
: identical toseach_with_index
. -
with_object(<obj>)
: identical toseach_with_object
. -
clone
: create a new enumerator on the same elements. -
speek
: returns the current element pointed by the enumerator without advancing it. -
snext
: returns the current element pointed by the enumerator and goes to the next one. -
srewind
: restart the enumeration. -
+
: concatenation of enumerators.
It is also possible to define a custom enumerator using the following command:
<<span class="pl-en">enum</span>> <span class="pl-c1">=</span> <span class="pl-en">senumerator</span><span class="pl-kos">(</span><<span class="pl-en">typ</span>><span class="pl-kos">,</span><<span class="pl-en">size</span>><span class="pl-kos">)</span> <<span class="pl-en">block</span>><span class="pl-en"></span>
Where enum
is a Ruby variable referring to the enumerator, typ
is the data type and size
is the number of the elements to enumerate and block
is the block that implements the access to an element by index. For example, an enumerator on a memory could be defined as follows:
<span class="pl-en">bit</span><span class="pl-kos">[</span><span class="pl-c1">8</span><span class="pl-kos">]</span><span class="pl-kos">[</span>-<span class="pl-c1">8</span><span class="pl-kos">]</span><span class="pl-kos">.</span><span class="pl-en">inner</span> <span class="pl-pds">mem</span>: <span class="pl-kos">[</span> <span class="pl-en">_h01</span><span class="pl-kos">,</span> <span class="pl-en">_h02</span><span class="pl-kos">,</span> <span class="pl-en">_h03</span><span class="pl-kos">,</span> <span class="pl-en">_h04</span><span class="pl-kos">,</span> <span class="pl-en">_h30</span><span class="pl-kos">,</span> <span class="pl-en">_h30</span><span class="pl-kos">,</span> <span class="pl-en">_h30</span><span class="pl-kos">,</span> <span class="pl-en">_h30</span> <span class="pl-kos">]</span>
<span class="pl-kos">[</span><span class="pl-c1">3</span><span class="pl-kos">]</span><span class="pl-kos">.</span><span class="pl-en">inner</span> <span class="pl-pds">:addr</span>
<span class="pl-kos">[</span><span class="pl-c1">8</span><span class="pl-kos">]</span><span class="pl-kos">.</span><span class="pl-en">inner</span> <span class="pl-pds">:data</span>
<span class="pl-en">data</span> <= <span class="pl-en">mem</span><span class="pl-kos">[</span><span class="pl-en">addr</span><span class="pl-kos">]</span>
<span class="pl-s1">mem_enum</span> <span class="pl-c1">=</span> <span class="pl-en">senumerator</span><span class="pl-kos">(</span><span class="pl-en">bit</span><span class="pl-kos">[</span><span class="pl-c1">8</span><span class="pl-kos">]</span><span class="pl-kos">,</span><span class="pl-c1">8</span><span class="pl-kos">)</span> <span class="pl-k">do</span> |<span class="pl-s1">i</span>|
<span class="pl-en">addr</span> <= <span class="pl-s1">i</span>
<span class="pl-en">step</span>
<span class="pl-en">data</span>
<span class="pl-k">end</span>
In the code above, mem_enum
is the variable referring to the resulting enumerator built for accessing memory mem
. For the access, it is assumed that one cycle must be waited after the address is sets, and therefore a step
command is added in the access procedure before data
can be returned.
With this basis, several algorithms have been implemented using enumerators and are usable for all the enumerable objects. All these algorithms are HW implantation of the Ruby Enumerable methods. They are accessible using the corresponding ruby method prefixed by character s
. For example, the HW implementation of the ruby all?
method is generated by the sall?
method. In details:
-
sall?
: HW implementation of the Rubyall?
method. Returns a single-bit signal. When 0 this value means false and when 1 it means true. -
sany?
: HW implementation of the Rubyany?
method. Returns a single-bit signal. When 0 this value means false and when 1 it means true. -
schain
: HW implementation of the Rubychain
. -
smap
: HW implementation of the Rubymap
method. When used with a block returns a vector signal containing each computation result. -
scompact
: HW implementation of the Rubycompact
method. However, since there is no nil value in HW, use 0 instead for compacting. Returns a vector signal containing the compaction result. -
scount
: HW implementation of the Rubycount
method. Returns a signal whose bit width matches the size of the enumerator containing the count result. -
scycle
: HW implementation of the Rubycycle
method. -
sfind
: HW implementation of the Rubyfind
method. Returns a signal containing the found element, or 0 if not found. -
sdrop
: HW implementation of the Rubydrop
method. Returns a vector signal containing the remaining elements. -
sdrop_while
: HW implementation of the Rubydrop_while
method. Returns a vector signal containing the remaining elements. -
seach_cons
: HW implementation of the Rubyeach_cons
method. -
seach_slice
: HW implementation of the Rubyeach_slice
method. -
seach_with_index
: HW implementation of the Rubyeach_with_index
method. -
seach_with_object
: HW implementation of the Rubyeach_with_object
method. -
sto_a
: HW implementation of the Rubyto_a
method. Returns a vector signal containing all the elements of the enumerator. -
sselect
: HW implementation of the Rubyselect
method. Returns a vector signal containing the selected elements. -
sfind_index
: HW implementation of the Rubyfind_index
method. Returns the index of the found element or -1 if not. -
sfirst
: HW implementation of the Rubyfirst
method. Returns a vector signal containing the first elements. -
sinclude?
: HW implementation of the Rubyinclude?
method. Returns a single-bit signal. When 0 this value means false and when 1 it means true. -
sinject
: HW implementation of the Rubyinject
method. Return a signal of the type of elements containing the computation result. -
smax
: HW implementation of the Rubymax
method. Return a vector signal containing the found max values. -
smax_by
: HW implementation of the Rubymax_by
method. Return a vector signal containing the found max values. -
smin
: HW implementation of the Rubymin
method. Return a vector signal containing the found min values. -
smin_by
: HW implementation of the Rubymin_by
method. Return a vector signal containing the found min values. -
sminmax
: HW implementation of the Rubyminmax
method. Returns a 2-element vector signal containing the resulting min and max values. -
sminmax_by
: HW implementation of the Rubyminmax_by
method. Returns a 2-element vector signal containing the resulting min and max values. -
snone?
: HW implementation of the Rubynone?
method. Returns a single-bit signal. When 0 this value means false and when 1 it means true. -
sone?
: HW implementation of the Rubyone?
method. Returns a single-bit signal. When 0 this value means false and when 1 it means true. -
sreject
: HW implementation of the Rubyreject
method. Returns a vector signal containing the remaining elements. -
sreverse_each
: HW implementation of the Rubyreverse_each
method. -
ssort
: HW implementation of the Rubysort
method. Returns a vector signal containing the sorted elements. -
ssort_by
: HW implementation of the Rubysort_by
method. Returns a vector signal containing the sorted elements. -
ssum
: HW implementation of the Rubysum
method. Returns a signal with the type of elements containing the sum result. -
stake
: HW implementation of the Rubytake
method. Returns a vector signal containing the taken elements. -
stake_while
: HW implementation of the Rubytake_while
method. Returns a vector signal containing the taken elements. -
suniq
: HW implementation the Rubyuniq
method. Returns a vector signal containing the selected elements.
std/sequencer_sync.rb
Shared signals, arbiters and monitors:
Shared signals
Like any other processes, It is not possible for several sequencers to write to the same signal. This is because there would be race competition that may destroy physically the device if such operations where authorized. In standard RTL design, this limitation is overcome by implementing three-state buses, multiplexers and arbiters. However, HDLRuby sequencers supports another kind of signals called the shared signals that abstract the implementation details for avoiding race competition.
The shared signals are declared like the other kind of signals from their type. The syntax is the following:
<<span class="pl-en">type</span>><span class="pl-kos">.</span><span class="pl-en">shared</span> <<span class="pl-en">list</span> <span class="pl-en">of</span> <span class="pl-en">names</span>><span class="pl-en"></span>
They can also have an initial (and default) value when declared as follows:
<<span class="pl-en">type</span>><span class="pl-kos">.</span><span class="pl-en">shared</span> <<span class="pl-en">list</span> <span class="pl-en">of</span> <span class="pl-en">names</span> <span class="pl-en">with</span> <span class="pl-en">initialization</span>><span class="pl-en"></span>
For example the following code declare two 8-bit shared signals x
and y
and two signed 16-bit shared signals initialized to 0 u
and v
:
[8].shared :x, :y
signed[8].shared u: 0, v: 0
A shared signals can then be read and written to by any sequencer from anywhere in the subsequent code of the current scope. However, they cannot be written to outside a sequencer. For example, the following code is valid:
input :clk, :start
[8].inner :val0, :val1
[8].shared :x, :y
val0 <= x+y
par(clk.posedge) { val1 <= x+y }
sequencer(clk.posedge,start) do
10.stimes { |i| x <= i }
end
sequencer(clk.posedge,start) do
5.stimes { |i| x <= i*2 ; y <= i*2 }
end
But the following code is not valid:
[8].shared w: 0
par(clk.posedge) { w <= w + 1 }
By default, a shared signal acknowledge writing from the first sequencer that access it in order of declaration, the others are ignored. In the first example given above, that means for signal x
the value is always the one written by the first sequencer, i.e., from 0 to 9 changing once per clock cycle. However, the value of signal y
is set by the second sequencer since it is this one only that writes to this signal.
This default behavior of shared signal avoids race competition, but is not very useful in practice. For a better control, it is possible to select which sequencer is to be acknowledged for writing. This is done by setting the number of the sequencer which can write the signal that controls the sharing accessed as follows:
<<span class="pl-en">shared</span> <span class="pl-en">signal</span>><span class="pl-kos">.</span><span class="pl-en">select</span>
The select value starts from 0 for the first sequencer writing to the shared signal, and is increased by one per writing sequencer. For example, in the first example, for selecting the second sequencer for writing to x
the follow code can be added after this signal is declared:
<span class="pl-en">x</span><span class="pl-kos">.</span><span class="pl-en">select</span> <= <span class="pl-c1">1</span>
This value can be changed at runtime too. For example, instead of setting the second sequencer, it is possible to switch sequencer every clock cycle as follows:
<span class="pl-en">par</span><span class="pl-kos">(</span><span class="pl-en">clk</span><span class="pl-kos">.</span><span class="pl-en">posedge</span><span class="pl-kos">)</span> <span class="pl-kos">{</span> <span class="pl-en">x</span><span class="pl-kos">.</span><span class="pl-en">select</span> <= <span class="pl-en">x</span><span class="pl-kos">.</span><span class="pl-en">select</span> + <span class="pl-c1">1</span> <span class="pl-kos">}</span>
Note: this select sub signal is a standard RTL signal that has the same properties and limitations as the other ones, i.e., this is not a shared signal itself.
Arbiters
Usually, it is not the signals that we want to share, but the resources they drives. For example, in a CPU, it is an ALU that is shared as a whole rather than each of its input separately. In order to support such cases and ease the handling of shared signals, the library also provides the arbiter components. This component is instantiated like a standard module as follows, where name
is the name of the arbiter instance:
arbiter(:>).(<list of shared signal>)
When instantiated, an arbiter will take control of the select sub signals of the shared signals (hence, you cannot control the selection yourself for them any longer). In returns, it provides the possibility of requiring or releasing access to the shared signals. Requiring access is done by sending the value 1 to the arbiter, and releasing is done by sending the value 0. If a sequencer writes to a shared signal under arbitration without requiring access first, the write will simply be ignored.
The following is an example of arbiter that controls access to shared signals x
and y
and two sequencers acquiring and releasing accesses to them:
input :clk, :start
[8].shared x, y
arbiter(:ctrl_xy).(x,y)
sequencer(clk.posedge,start) do
ctrl_xy <= 1
x <= 0 ; y <= 0
5.stime do |i|
x <= x + 1
y <= y + 2
end
ctrl_xy <= 0
end
sequencer(clk.posedge,start) do
ctrl_xy <= 1
x <= 2; y <= 1
10.stime do |i|
x <= x + 2
y <= y + 1
end
ctrl_xy <= 0
end
In the example, both sequencers require access to signals x
and y
before accessing them and then releasing the access.
Requiring access does not guaranties that the access will be granted by the arbiter though. In the access is not granted, the write access will be ignored.
The default access granting policy of an arbiter is the priority in order of sequencer declaration. I.e., if several sequencer are requiring at the same time, then the one declared the earliest in the code gains write access. For example, with the code given about, the first sequencer have write access to x
and y
, and since after five write cycles it releases access, the second sequencer can then write to these signals. However, not obtaining write access does not block the execution of the sequencer, simply, its write access to the corresponding shared signals is simple ignored. In the example, the second sequencer will do its first five loop cycles without any effect, and have only its five last ones that change the shared signals. To avoid such a behavior, it is possible to check if the write access is granted using arbiter sub signal acquired
: if this signal is one in current sequencer, that means the access is granted, otherwise its is 0. For example the following will increase signal x
only if write access is granted:
hif(ctrl_xy.acquired) { x <= x + 1 }
The policy of an arbiter can be changed using command policy. You can either provide a new priority table, containing the number of the sequencers in order of priority (the first one having higher priority. The number of a sequencer is assign in order of declaration provided it uses the arbiter. For example, in the previous code, the second sequencer can be given higher priority by adding the following code after having declared the arbiter:
ctrl_xy.policy([1,0])
It is also possible to set a more complex policy by providing to the policy method a block of code whose argument is a vector indicating which sequencer is currently requiring write access to the shared signals and whose result will be the number of the sequencer to grant the access. This code will be executing each time an write access is actually performed. For example, in the previous code, a policy switch priorities at each access can be implemented as follows:
inner priority_xy: 0
inner grant_xy
ctrl_xy.policy do |acq|
hcase(acq)
hwhen(_b01) do
grant_xy <= 0
priority_xy <= ~priority_xy
end
hwhen(_b10) do
grant_xy <= 1
priority_xy <= ~priority_xy
end
hwhen(_b11) do
grant_xy <= priority_xy
priority_xy <= ~priority_xy
end
grant_xy
end
As seen in the code above, each bit of the acq
vector is one when the corresponding sequencer required an access or 0 otherwise, bit 0 corresponding to sequencer 0, bit 1 to sequencer 1 and so one.
Monitors
Arbiters a especially useful when we can ensure that the sequencers accessing the same resource do not overlap or when the do not need to synchronize with each other. If such synchronizations are required, instead of arbiters, it is possible to use the monitor components.
The monitor component are instantiated like the arbiters as follows:
monitor(:>).(<list of shared signals>)
Monitors are used exactly the same ways as arbiters (including the write access granting policies), but blocks the execution of the sequencers that require a write access until the access is granted. If we take the example of code with two sequencers given as illustration of arbiter usage, replacing the arbiter by a monitor as follows will lock the second sequencer until it can write to shared variables x
and y
ensuring that all its loop cycles have the specified result:
monitor(:ctrl_xy).(x,y)
Since monitors locks processes, it automatically insert a step, hence to avoid confusion, aquiring access to a monitor is done by using method lock
instead of assigning 1, and releasing is done by using method unlock
instead of assigning 0. Hence, when using a monitor, the previous arbiter-based code should be rewriten as follows:
input :clk, :start
[8].shared x, y
monitor(:ctrl_xy).(x,y)
sequencer(clk.posedge,start) do
ctrl_xy.lock
x <= 0 ; y <= 0
5.stime do |i|
x <= x + 1
y <= y + 2
end
ctrl_xy.unlock
end
sequencer(clk.posedge,start) do
ctrl_xy.lock
x <= 2; y <= 1
10.stime do |i|
x <= x + 2
y <= y + 1
end
ctrl_xy.unlock
end
std/fixpoint.rb
Fixed-point (fixpoint):
This library provides a new fixed point set of data types. These new data types can be bit vectors, unsigned or signed values and are declared respectively as follows:
bit[<integer part range>,<fractional part range>]
unsigned[<integer part range>,<fractional part range>]
signed[<integer part range>,<fractional part range>]
For example, a signed 4-bit integer part 4-bit fractional part fixed point inner signal named sig
can be declared as follows:
bit[4,4].inner :sig
When performing computation with fixed-point types, HDLRuby ensures that the result's decimal point position is correct.
In addition to the fixed point data type, a method is added to the literal objects (Numeric) to convert them to fixed-point representation:
<<span class="pl-en">litteral</span>><span class="pl-kos">.</span><span class="pl-en">to_fix</span><span class="pl-kos">(</span><<span class="pl-en">number</span> <span class="pl-en">of</span> <span class="pl-en">bits</span> <span class="pl-en">after</span> <span class="pl-en">the</span> <span class="pl-en">decimal</span> <span class="pl-en">point</span>><span class="pl-c1"></span><span class="pl-kos">)</span>
For example, the following code converts a floating-point value to a fixed-point value with 16 bits after the decimal point:
3.178.to_fix(16)
std/channel.rb
Channel:
This library provides a unified interface to complex communication protocols through a new kind of component called the channels that abstract the details of communication protocols. The channels can be used similarly to the ports of a system and are used through a unified interface so that changing the kind of channel, i.e., the communication protocol, does not require any modification of the code.
Using a channel
A channel is used similarly to a pipe: it has an input where data can be written and an output where data can be read. The ordering of the data and the synchronization depend on the internals of the channel, e.g., a channel can be FIFO or LIFO. The interaction with the channel is done using the following methods:
-
write(<args>) <block>
: write to the channel and executeblock
whenwrite
completes.args
is a list of arguments required for performing the write that depends on the channel. -
read(<args>) <block>
: read the channel and executeblock
when the read completes.args
is a list of arguments required for performing the write that depends on the channel.
For example, a system sending successive 8-bit values through a channel can be described as follows:
system :producer8 do |channel|
# Inputs of the producer: clock and reset.
input :clk, :rst
# Inner 8-bit counter for generating values.
[8].inner :counter
# The value production process
par(clk.posedge) do
hif(rst) { counter <= 0 }
helse do
channel.write(counter) { counter <= counter + 1 }
end
end
end
Note: In the code above, the channel is passed as a generic argument of the system.
The access points to a channel can also be handled individually by declaring ports using the following methods:
-
input <name>
: declares a port for reading from the channel and associates them toname
if any -
output <name>
: declares a port for writing to the channel and associates them toname
if any -
inout <name>
: declares a port for reading and writing to the channel and associates them toname
if any
Such a port can then be accessed using the same read
and write
method of a channel, the difference being that they can also be configured for new access procedures using the wrap
method:
-
wrap(<args>) <code>
: creates a new port whose read or write procedure has the elements of<args>
and the ones produced by<code>
assigned to the arguments of the read or write procedure.
For example, assuming mem
is a channel whose read and write access have as argument the target address and data signals, the following code creates a port for always accessing at address 0:
<span class="pl-s1">addr0</span> <span class="pl-c1">=</span> <span class="pl-en">channel</span><span class="pl-kos">.</span><span class="pl-en">input</span><span class="pl-kos">.</span><span class="pl-en">wrap</span><span class="pl-kos">(</span><span class="pl-c1">0</span><span class="pl-kos">)</span>
Channel branches
Some channels may include several branches, they are accessed by name using the following method:
-
branch(<name>)
: gets branch namedname
from the channel. This name can be any ruby object (e.g., a number) but it will be converted internally to a ruby symbol.
A branch is a full-fledged channel and is used identically. For instance, the following code gets access to branch number 0 of channel ch
, gets its inputs port, reads it, and put the result in signal val
on the rising edges of signal clk
:
br = ch.branch(0)
br.input
par(clk.posedge) { br.read(val) }
Declaring a channel
A new channel is declared using the keyword channel
as follows:
channel <name> <block>
Where name
is the name of the channel and block
is a procedure block describing the channel. This block can contain any HDLRuby code, and is comparable to the content of a block describing a system with the difference that it does not have standard input, output, and inout ports are declared differently, and that it supports the following additional keywords:
-
reader_input <list of names>
: declares the input ports on the reader side. The list must give the names of the inner signals of the channel that can be read using the reader procedure. -
reader_output <list of names>
: declares the output ports on the reader side. The list must give the names of the inner signals of the channel that can be written using the reader procedure. -
reader_inout <list of names>
: declares the inout ports on the reader side. The list must give the names of the inner signals of the channel that can be written using the reader procedure. -
writer_input <list of names>
: declares the input ports on the writer side. The list must give the names of the inner signals of the channel that can be read using the writer procedure. -
writer_output <list of names>
: declares the output ports on the writer side. The list must give the names of the inner signals of the channel that can be written using the writer procedure. -
writer_inout <list of names>
: declares the inout ports on the writer side. The list must give the names of the inner signals of the channel that can be written using the writer procedure. -
accesser_input <list of names>
: declares the input ports on both the reader and writer sides. The list must give the names of the inner signals of the channel that can be read using the writer procedure. -
accesser_output <list of names>
: declares the output ports on both the reader and writer sides. The list must give the names of the inner signals of the channel that can be written using the writer procedure. -
accesser_inout <list of names>
: declares the inout ports on both the reader and writer sides. The list must give the names of the inner signals of the channel that can be written using the writer procedure. -
reader <block>
: defines the reader's access procedure. This procedure is invoked by the methodread
of the channel (please refer to the previous example). The first argument of the block must be the following:-
blk
: the block to execute when the read completes. Other arguments can be freely defined and will be required by theread
method.
-
-
writer < block>
: defines the writer's access procedure. This procedure is invoked by the methodwrite
of the channel (please refer to the previous example). The first argument of the block must be the following:-
blk
: the block to execute when the write completes. Other arguments can be freely defined and will be required by thewrite
command.
-
-
brancher(name) <block>
: defines branch named +name+ described inblock
. The content of the block can be any content valid for a channel, with the additional possibility to access the internals of the upper channel.
For example, a channel implemented by a simple register of generic type typ
, that can be set to 0 using the reset
command can be described as follows:
channel :regch do |typ|
# The register.
typ.inner :reg
# The reader procedure can read reg
reader_input :reg
# The writer procedure can write reg
writer_output :reg
# Declares a reset
command(:reset) { reg <= 0 }
# Defines the reader procedure.
reader do |blk,target|
target <= reg
blk.call if blk
end
# Defines the writer procedure.
writer do |blk,target|
reg <= target
blk.call if blk
end
end
Notes:
- The described channel assumes that the
write
method of the channel is invoked within a clocked process (otherwise, the register will become a latch). - The described channel supports the
read
andwrite
methods to be invoked with or without a block.
Like systems, a channel must be instantiated for being used, and the instantiation procedure is identical:
<<span class="pl-en">channel</span> <span class="pl-en">name</span>> <span class="pl-pds">:<instance</span> <span class="pl-en">name</span>><span class="pl-en"></span>
And in case there is a generic parameter, the instantiation procedure is as follows:
<<span class="pl-en">channel</span> <span class="pl-en">name</span>><span class="pl-kos">(</span><span class="pl-pds">:<instance</span> <span class="pl-en">name</span>><span class="pl-en"></span><span class="pl-kos">)</span><span class="pl-kos">.</span><span class="pl-kos">(</span><<span class="pl-en">generic</span> <span class="pl-en">parameters</span>><span class="pl-c1"></span><span class="pl-kos">)</span>
After a channel is instantiated, it must be linked to the circuits that will communicate through it. This is done when instantiating these circuits. If a circuit reads or writes on the channel, it will be instantiated as follows:
<<span class="pl-en">system</span> <span class="pl-en">name</span>><span class="pl-kos">(</span><<span class="pl-en">channel</span> <span class="pl-en">instance</span>><span class="pl-en"></span><span class="pl-kos">)</span><span class="pl-kos">.</span><span class="pl-kos">(</span><span class="pl-pds">:<instance</span> <span class="pl-en">name</span>><span class="pl-en"></span><span class="pl-kos">)</span><span class="pl-kos">.</span><span class="pl-kos">(</span><<span class="pl-en">circuit</span> <span class="pl-en">standard</span> <span class="pl-en">connections</span>><span class="pl-c1"></span><span class="pl-kos">)</span>
Notes:
- It is possible for a circuit to access several channels. For that purpose, each channel must be passed as generic arguments, and their corresponding
reader_signals
andwriter_signals
are to be put in the order of declaration. - It is also possible for a circuit to read and write on the same channel. For that purpose, the channel will be passed several times as generic arguments, and the corresponding
reader_signals
andwriter_signals
are to be put in the order of declaration.
The following code is an example instantiating the register channel presented above for connecting an instance of producer8
and another circuit called consumer8
:
# System wrapping the producer and the consumer circuits.
system :producer_consumer8 do
# The clock and reset of the circuits
input :clk, :rst
# Instance of the channel (using 8-bit data).
regch([8]).(:regchI)
# Reset the channel on positive edges of signal rst.
regchI.reset.at(rst.posedge)
# Instantiate the producer.
producer8(regch).(:producerI).(clk,rst)
# Instantiate the consumer.
consumer8(regch).(:consumerI).(clk.rst)
end
Note:
- The code of the circuits, in the examples
producer8
,consumer8
, andproducer_consummer8
is independent of the content of the channel. For example, the samplewith_channel.rb
(please see samples) uses the same circuits with a channel implementing handshaking.
Sample HDLRuby descriptions
Several samples HDLRuby descriptions are available in the following directory:
path/to/HDLRuby/lib/HDLRuby/hdr_samples
For the gem install, the path to HDLRuby can be found using the following:
But you can also import the samples to your local directory with the following command (recommended):
hdrcc --get-samples
The naming convention of the samples is the following:
-
<name>.rb
: default type of sample. -
<name>_gen.rb
: generic parameters are required for processing the sample. -
<name>_bench.rb
: sample including a simulation benchmark, these are the only samples that can be simulated usinghdrcc -S
. Please notice that such a sample cannot be converted to VHDL or Verilog HDL yet. -
with_<name>.rb
: sample illustrating a single aspect of HDLRuby or one of its library, usually includes a benchmark.
Contributing
Bug reports and pull requests are welcome on GitHub at https://github.com/civol/HDLRuby.
To do
- Find and fix the (maybe) terrifying number of bugs.
- Add a GUI (any volunteer to do it?).
License
The gem is available as open-source under the terms of the MIT License.