Class: N65::Instruction

Inherits:
Object
  • Object
show all
Includes:
Regexes
Defined in:
lib/n65/instruction.rb

Overview

Represents a single 6502 Instruction

Defined Under Namespace

Classes: AddressOutOfRange, ArgumentTooLarge, InvalidAddressingMode, InvalidInstruction, UnresolvedSymbols

Constant Summary collapse

ADDRESSING_MODES = 
{
  relative: {
    example: 'B** my_label',
    display: '%s $%.4X',
    regex: /$^/i,
    regex_label: /^#{Branches}\s+#{Sym}$/
  },

  immediate: {
    example: 'AAA #$FF',
    display: '%s #$%.2X',
    regex: /^#{Mnemonic}\s+#{Immediate}$/,
    regex_label: /^#{Mnemonic}\s+#(<|>)#{Sym}$/
  },

  implied: {
    example: 'AAA',
    display: '%s',
    regex: /^#{Mnemonic}$/
  },

  zero_page: {
    example: 'AAA $FF',
    display: '%s $%.2X',
    regex: /^#{Mnemonic}\s+#{Num8}$/,
    regex_label: /^#{Mnemonic}\s+#{Sym}\s+zp$/
  },

  zero_page_x: {
    example: 'AAA $FF, X',
    display: '%s $%.2X, X',
    regex: /^#{Mnemonic}\s+#{Num8}\s?,\s?#{XReg}$/,
    regex_label: /^#{Mnemonic}\s+#{Sym}\s?,\s?#{XReg}\s+zp$/
  },

  zero_page_y: {
    example: 'AAA $FF, Y',
    display: '%s $%.2X, Y',
    regex: /^#{Mnemonic}\s+#{Num8}\s?,\s?#{YReg}$/,
    regex_label: /^#{Mnemonic}\s+#{Sym}\s?,\s?#{YReg}\s+zp$/
  },

  absolute: {
    example: 'AAA $FFFF',
    display: '%s $%.4X',
    regex: /^#{Mnemonic}\s+#{Num16}$/,
    regex_label: /^#{Mnemonic}\s+#{Sym}$/
  },

  absolute_x: {
    example: 'AAA $FFFF, X',
    display: '%s $%.4X, X',
    regex: /^#{Mnemonic}\s+#{Num16}\s?,\s?#{XReg}$/,
    regex_label: /^#{Mnemonic}\s+#{Sym}\s?,\s?#{XReg}$/
  },

  absolute_y: {
    example: 'AAA $FFFF, Y',
    display: '%s $%.4X, Y',
    regex: /^#{Mnemonic}\s+#{Num16}\s?,\s?#{YReg}$/,
    regex_label: /^#{Mnemonic}\s+#{Sym}\s?,\s?#{YReg}$/
  },

  indirect: {
    example: 'AAA ($FFFF)',
    display: '%s ($%.4X)',
    regex: /^#{Mnemonic}\s+\(#{Num16}\)$/,
    regex_label: /^#{Mnemonic}\s+\(#{Sym}\)$/
  },

  indirect_x: {
    example: 'AAA ($FF, X)',
    display: '%s ($%.2X, X)',
    regex: /^#{Mnemonic}\s+\(#{Num8}\s?,\s?#{XReg}\)$/,
    regex_label: /^#{Mnemonic}\s+\(#{Sym}\s?,\s?#{XReg}\)$/
  },

  indirect_y: {
    example: 'AAA ($FF), Y)',
    display: '%s ($%.2X), Y',
    regex: /^#{Mnemonic}\s+\(#{Num8}\)\s?,\s?#{YReg}$/,
    regex_label: /^#{Mnemonic}\s+\(#{Sym}\)\s?,\s?#{YReg}$/
  }
}.freeze

Constants included from Regexes

Regexes::Bin16, Regexes::Bin8, Regexes::Branches, Regexes::Hex16, Regexes::Hex8, Regexes::Immediate, Regexes::Mnemonic, Regexes::Num16, Regexes::Num8, Regexes::Sym, Regexes::XReg, Regexes::YReg

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(op, arg, mode, byte_selector = nil) ⇒ Instruction

Create an instruction. Having the instruction op a downcased symbol is nice because that can later be used to index into our opcodes hash in OpCodes OpCodes contains the definitions of each OpCode

Raises:



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# File 'lib/n65/instruction.rb', line 167

def initialize(op, arg, mode, byte_selector = nil)
  @byte_selector = byte_selector.nil? ? nil : byte_selector.to_sym
  raise(InvalidInstruction, "Bad Byte selector: #{byte_selector}") unless [:>, :<, nil].include?(@byte_selector)

  ##  Lookup the definition of this opcode, otherwise it is an invalid instruction
  @op = op.downcase.to_sym
  definition = OpCodes[@op]
  raise(InvalidInstruction, op) if definition.nil?

  @arg = arg

  # Be sure the mode is an actually supported mode.
  @mode = mode.to_sym
  raise(InvalidAddressingMode, mode) unless ADDRESSING_MODES.key?(@mode)
  raise(InvalidInstruction, "#{op} cannot be used in #{mode} mode") if definition[@mode].nil?

  @description, @flags = definition.values_at(:description, :flags)
  @hex, @length, @cycles, @boundry_add = definition[@mode].values_at(:hex, :len, :cycles, :boundry_add)
end

Instance Attribute Details

#address ⇒ Object (readonly)

Returns the value of attribute address.



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# File 'lib/n65/instruction.rb', line 9

def address
  @address
end

#arg ⇒ Object (readonly)

Returns the value of attribute arg.



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# File 'lib/n65/instruction.rb', line 9

def arg
  @arg
end

#boundry_add ⇒ Object (readonly)

Returns the value of attribute boundry_add.



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# File 'lib/n65/instruction.rb', line 9

def boundry_add
  @boundry_add
end

#cycles ⇒ Object (readonly)

Returns the value of attribute cycles.



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# File 'lib/n65/instruction.rb', line 9

def cycles
  @cycles
end

#description ⇒ Object (readonly)

Returns the value of attribute description.



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# File 'lib/n65/instruction.rb', line 9

def description
  @description
end

#flags ⇒ Object (readonly)

Returns the value of attribute flags.



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# File 'lib/n65/instruction.rb', line 9

def flags
  @flags
end

#hex ⇒ Object (readonly)

Returns the value of attribute hex.



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# File 'lib/n65/instruction.rb', line 9

def hex
  @hex
end

#length ⇒ Object (readonly)

Returns the value of attribute length.



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# File 'lib/n65/instruction.rb', line 9

def length
  @length
end

#mode ⇒ Object (readonly)

Returns the value of attribute mode.



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# File 'lib/n65/instruction.rb', line 9

def mode
  @mode
end

#op ⇒ Object (readonly)

Returns the value of attribute op.



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# File 'lib/n65/instruction.rb', line 9

def op
  @op
end

Class Method Details

.parse(line) ⇒ Object

Parse one line of assembly, returns nil if the line is ultimately empty of asm instructions Raises SyntaxError if the line is malformed in some way

Raises:

  • (SyntaxError) 


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# File 'lib/n65/instruction.rb', line 109

def self.parse(line)
  # Try to parse this line in each addressing mode
  ADDRESSING_MODES.each do |mode, parse_info|
    # We have regexes that match each addressing mode
    match_data = parse_info[:regex].match(line)

    unless match_data.nil?
      # We must have a straight instruction without symbols, construct
      # an Instruction from the match_data, and return it
      _, op, arg_hex, arg_bin = match_data.to_a

      # Until I think of something better, it seems that the union regex
      # puts a hexidecimal argument in one capture, and a binary in the next
      # This is annoying, but still not as annoying as using Treetop to parse
      if !arg_hex.nil?
        return Instruction.new(op, arg_hex.to_i(16), mode)
      elsif !arg_bin.nil?
        return Instruction.new(op, arg_bin.to_i(2), mode)
      else
        return Instruction.new(op, nil, mode)
      end

    else
      # Can this addressing mode even use labels?
      unless parse_info[:regex_label].nil?

        # See if it does in fact have a symbolic argument
        match_data = parse_info[:regex_label].match(line)

        unless match_data.nil?
          # We have found an assembly instruction containing a symbolic
          # argument.  We can resolve this symbol later by looking at the
          # symbol table in the #exec method
          match_array = match_data.to_a

          # If we have a 4 element array, this means we matched something
          # like LDA #<label, which is a legal immediate one byte value
          # by taking the msb.  We need to make that distinction in the
          # Instruction, by passing an extra argument
          if match_array.size == 4
            _, op, byte_selector, arg = match_array
            return Instruction.new(op, arg, mode, byte_selector.to_sym)
          else
            _, op, arg = match_array
            return Instruction.new(op, arg, mode)
          end
        end
      end
    end
  end

  # We just don't recognize this line of asm, it must be a Syntax Error
  raise(SyntaxError, line)
end

Instance Method Details

#apply_byte_selector(byte_selector, value) ⇒ Object

Apply a byte selector to an argument



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# File 'lib/n65/instruction.rb', line 226

def apply_byte_selector(byte_selector, value)
  return value if byte_selector.nil?

  case byte_selector
  when :>
    high_byte(value)
  when :<
    low_byte(value)
  end
end

#emit_bytes ⇒ Object

Emit bytes from asm structure



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# File 'lib/n65/instruction.rb', line 238

def emit_bytes
  case @length
  when 1
    [@hex]
  when 2
    if zero_page_instruction? && @arg.negative? || @arg > 0xff
      raise(ArgumentTooLarge, "For #{@op} in #{@mode} mode, only 8-bit values are allowed")
    end

    [@hex, @arg]
  when 3
    [@hex] + break_16(@arg)
  else
    raise("Can't handle instructions > 3 bytes")
  end
end

#exec(assembler) ⇒ Object

Execute writes the emitted bytes to virtual memory, and updates PC If there is a symbolic argument, we can try to resolve it now, or promise to resolve it later.



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# File 'lib/n65/instruction.rb', line 195

def exec(assembler)
  promise = assembler.with_saved_state do |saved_assembler|
    @arg = saved_assembler.symbol_table.resolve_symbol(@arg)

    # If the instruction uses a byte selector, we need to apply that.
    @arg = apply_byte_selector(@byte_selector, @arg)

    # If the instruction is relative we need to work out how far away it is
    @arg = @arg - saved_assembler.program_counter - 2 if @mode == :relative

    saved_assembler.write_memory(emit_bytes)
  end

  case @arg
  when Integer, NilClass
    assembler.write_memory(emit_bytes)
  when String
    begin
      # This works correctly now :)
      promise.call
    rescue SymbolTable::UndefinedSymbol
      placeholder = [@hex, 0xDE, 0xAD][0...@length]
      # I still have to write a placeholder instruction of the right
      # length.  The promise will come back and resolve the address.
      assembler.write_memory(placeholder)
      promise
    end
  end
end

#zero_page_instruction? ⇒ Boolean

Is this instruction a zero page instruction?

Returns:

  • (Boolean) 


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# File 'lib/n65/instruction.rb', line 188

def zero_page_instruction?
  %i[zero_page zero_page_x zero_page_y].include?(@mode)
end