Class: PSX::SIO0

Inherits:
Object
  • Object
show all
Defined in:
lib/psx/sio0.rb

Overview

SIO0: Controller and memory-card serial port.

The BIOS uses this to probe slots 1 and 2 every VBlank (“PadAutoPolling”): it pulls /JOYn low via JOY_CTRL, sends a series of bytes through JOY_DATA, and waits for the device to /ACK each byte. The /ACK signal latches as JOY_STAT bit 9 and raises IRQ_CONTROLLER (I_STAT bit 7). If no /ACK arrives within ~81 polling iterations the BIOS treats the slot as empty and moves on.

We model just enough of this to convince the BIOS that a digital pad is connected in slot 1 (so we get past PadAutoPolling and into the shell) and that nothing is in slot 2 / memory-card port (so the BIOS doesn’t wait for an empty memcard to respond). The host SDL keyboard feeds the button state through a callback supplied at construction time.

Constant Summary collapse

STAT_TX_READY_1 =

JOY_STAT (0x1F801044) bits

1 << 0
STAT_RX_FIFO_NE =

TX FIFO has room

1 << 1
STAT_TX_READY_2 =

RX FIFO not empty

1 << 2
STAT_RX_PARITY =

No active transfer / TX done

1 << 3
STAT_ACK_INPUT =

/ACK input level (0=device pulling low)

1 << 7
STAT_IRQ_REQUEST = 
1 << 9
CTRL_TXEN =

JOY_CTRL (0x1F80104A) bits

1 << 0
CTRL_JOYN_OUTPUT =

/JOYn output level (1 = device selected)

1 << 1
CTRL_RXEN = 
1 << 2
CTRL_ACK =

write 1 to reset IRQ + parity bits

1 << 4
CTRL_RESET =

write 1 to reset entire SIO state

1 << 6
CTRL_RX_INT_EN = 
1 << 11
CTRL_TX_INT_EN = 
1 << 10
CTRL_ACK_INT_EN = 
1 << 12
CTRL_SLOT =

0 = slot 1, 1 = slot 2

1 << 13
DIGITAL_PAD_IDHI =

Digital pad protocol response bytes

0x41
PAD_READY_BYTE = 
0x5A

Instance Method Summary collapse

Constructor Details

#initialize(interrupts: nil, controller_state: -> { 0xFFFF }) ⇒ SIO0

Returns a new instance of SIO0.



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# File 'lib/psx/sio0.rb', line 42

def initialize(interrupts: nil, controller_state: -> { 0xFFFF })
  @interrupts = interrupts
  @controller_state = controller_state
  reset_all
end

Instance Method Details

#read16(offset) ⇒ Object 



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# File 'lib/psx/sio0.rb', line 92

def read16(offset)
  case offset
  when 0x40 then pop_rx
  when 0x44 then status & 0xFFFF
  when 0x46 then (status >> 16) & 0xFFFF
  when 0x48 then @mode
  when 0x4A then @ctrl
  when 0x4E then @baud
  else 0
  end
end

#read32(offset) ⇒ Object 



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# File 'lib/psx/sio0.rb', line 104

def read32(offset)
  case offset
  when 0x40 then pop_rx
  when 0x44 then status
  when 0x48 then @mode | (@ctrl << 16)
  when 0x4C then @baud # unaligned but harmless
  else 0
  end
end

#read8(offset) ⇒ Object

Reads are byte-addressable; widen as needed for 16/32-bit accesses.



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# File 'lib/psx/sio0.rb', line 74

def read8(offset)
  case offset
  when 0x40 then pop_rx
  when 0x41, 0x42, 0x43 then 0
  when 0x44 then status & 0xFF
  when 0x45 then (status >> 8) & 0xFF
  when 0x46 then (status >> 16) & 0xFF
  when 0x47 then (status >> 24) & 0xFF
  when 0x48 then @mode & 0xFF
  when 0x49 then (@mode >> 8) & 0xFF
  when 0x4A then @ctrl & 0xFF
  when 0x4B then (@ctrl >> 8) & 0xFF
  when 0x4E then @baud & 0xFF
  when 0x4F then (@baud >> 8) & 0xFF
  else 0
  end
end

#reset_all ⇒ Object 



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# File 'lib/psx/sio0.rb', line 48

def reset_all
  @ctrl   = 0
  @mode   = 0
  @baud   = 0
  @rx     = []
  @irq    = false   # JOY_STAT bit 9 (and source of IRQ_CONTROLLER)
  @device_step = 0  # 0 = waiting for select byte
  @pending_ack_cycles = nil  # countdown before /ACK pulse fires
end

#status ⇒ Object

Read-side JOY_STAT word.



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# File 'lib/psx/sio0.rb', line 144

def status
  s = STAT_TX_READY_1 | STAT_TX_READY_2 | STAT_ACK_INPUT
  s |= STAT_RX_FIFO_NE unless @rx.empty?
  s |= STAT_IRQ_REQUEST if @irq
  s
end

#tick(cycles) ⇒ Object

Drive the /ACK timing. The BIOS clears I_STAT bit 7 right after writing JOY_DATA and only then enters the polling loop, so we must wait a beat before raising IRQ_CONTROLLER – otherwise the BIOS clear wipes our IRQ and the poll spins until timeout.



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# File 'lib/psx/sio0.rb', line 62

def tick(cycles)
  return unless @pending_ack_cycles
  @pending_ack_cycles -= cycles
  return if @pending_ack_cycles > 0
  @pending_ack_cycles = nil
  @irq = true
  @interrupts&.request(Interrupts::IRQ_CONTROLLER)
end

#write16(offset, value) ⇒ Object 



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# File 'lib/psx/sio0.rb', line 122

def write16(offset, value)
  case offset
  when 0x40 then transmit(value & 0xFF)
  when 0x48 then @mode = value & 0xFFFF
  when 0x4A then write_ctrl(value & 0xFFFF)
  when 0x4E then @baud = value & 0xFFFF
  end
end

#write32(offset, value) ⇒ Object 



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# File 'lib/psx/sio0.rb', line 131

def write32(offset, value)
  case offset
  when 0x40 then transmit(value & 0xFF)
  when 0x48
    @mode = value & 0xFFFF
    write_ctrl((value >> 16) & 0xFFFF)
  when 0x4C then @baud = value & 0xFFFF
  end
end

#write8(offset, value) ⇒ Object 



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# File 'lib/psx/sio0.rb', line 114

def write8(offset, value)
  case offset
  when 0x40 then transmit(value & 0xFF)
  when 0x4A then write_ctrl((@ctrl & 0xFF00) | (value & 0xFF))
  when 0x4B then write_ctrl((@ctrl & 0x00FF) | ((value & 0xFF) << 8))
  end
end