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README.md

Monotron I/O Controller

Introduction

This is the firmware for the Monotron's I/O controller. It is an Atmel AVR Atmega48, and it controls the:

  • PS/2 Keyboard port
  • PS/2 Mouse port
  • PC Printer (aka LPT, or Centronics) port

It talks to the main Monotron MCU over a serial link at 115,200 bps (8-data bits, no parity, 1 stop bit).

NB: As an interim test, there's an Arduino sketch in the keyboard folder which just emits raw scan-codes over the UART at 19,200 baud.

Compilation

This firmware builds with avr-gcc and meson.

$ meson --cross-file=./avr-cross.txt ./build
$ cd ./build
$ ninja # Builds a debug ELF and .hex file
$ ninja size # Tells you how big it is

Pinout

| Port | Pin | Direction | Name | Routed to | Description | |--------|-----|----------------|------------- -|------------|--------------------------| | B | 0 | Output | LPT_D0 | J13 pin 2 | LPT Output bit 0 | | B | 1 | Output | LPT_D1 | J13 pin 3 | LPT Output bit 1 | | B | 2 | Output | LPT_D2 | J13 pin 4 | LPT Output bit 2 | | B | 3 | Output | LPT_D3 | J13 pin 5 | LPT Output bit 3 | | B | 4 | Output | LPT_D4 | J13 pin 6 | LPT Output bit 4 | | B | 5 | Output | LPT_D5 | J13 pin 7 | LPT Output bit 5 | | B | 6 | Output | LPT_D6 | J13 pin 8 | LPT Output bit 6 | | B | 7 | Output | LPT_D7 | J13 pin 9 | LPT Output bit 7 | | C | 0 | I/O Open-drain | KB_CLK | J14 pin 5 | PS/2 Keyboard clock | | C | 1 | I/O Open-drain | MS_CLK | J15 pin 5 | PS/2 Mouse clock | | C | 2 | I/O Open-drain | KB_DATA | J14 pin 1 | PS/2 Keyboard data | | C | 3 | I/O Open-drain | MS_DATA | J15 pin 1 | PS/2 Mouse data | | C | 4 | Output | LPT_nINIT | J13 pin 16 | Initialise Printer | | C | 5 | Input | LPT_SEL | J13 pin 13 | Select (from printer) | | C | 6 | Output | LPT_nSELPRIN | J13 pin 17 | Select (to printer) | | D | 0 | Input | UART_RX | U1 PE1 | UART receive from MCU | | D | 1 | Output | UART_TX | U1 PE0 | UART transmit to MCU | | D | 2 | Input | LPT_nACK | J13 pin 10 | Acknowledge from Printer | | D | 3 | Input | LPT_BUSY | J13 pin 11 | Printer is Busy | | D | 4 | Input | LPT_nPE | J13 pin 12 | Printer found Paper End | | D | 5 | Input | LPT_nERROR | J13 pin 15 | Printer Error | | D | 6 | Output | LPT_nAUTOFEED | J13 pin 14 | Enable Auto Feed | | D | 7 | Output | LPT_nSTROBE | J13 pin 1 | Latch data |

Refer to the schematic for more details.

Protocol

The protocol between the I/O controller and the main MCU is pretty simple. As the MCU is pretty busy drawing the screen, and there's only a 16-byte UART FIFO on the MCU, we keep the I/O controller mostly quiet until commanded to send a packet of data. This will normally occur once per screen refesh (so, 60 Hz), which should be plenty for reading the keyboard and mouse.

Requests

These are the messages the MCU can send to the I/O controller. All are 1 byte long, but some have following bytes.

  • RESET_REQ (0x41) - Resets the attached keyboard and mouse as well as all status information.
  • PS2_DATA_REQ (0x42) - Requests all the keypresses and mouse movements since the last call.
  • PS2_LED_REQ (0x43) - Set the keyboard LEDs
  • LPT_DATA_REQ (0x44) - Write a byte to the 8-bit LPT port. If you are talking to a printer you have to pulse nSTROBE and poll the ACK signal manually. If you are using the port as GPIO then you can do what you like.
  • LPT_READ_REQ (0x45) - Read the status bits
  • LPT_CTRL_REQ (0x46) - Set the control bits:
    • Bit 0: nSTROBE
    • Bit 1: nAUTOFEED
    • Bit 2: nSELECT
    • Bit 3: INIT
  • LPT_BUFFERED_DATA_REQ (0x47) <bytes...> - Write a a number of bytes to a buffer. Each will be automatically clocked out with a pulse of the nSTROBE line, then waiting for the printer to raise and then lower the BUSY signal.
  • LPT_READ_PEND_REQ (0x48) - Send an indication when the pins specified by have the levels specified by . Use 0x00 and 0x00 to cancel an existing pend.
  • LPT_SET_MODE_REQ (0x49) - Try and configure a specific IEEE-1284 mode.
    • 0x00 - Compatibility mode
    • Other values reserved
  • PING_REQ (0x4A) - Empty request
  • BOOTLOADER_REQ (0x4B) - Go to firmware programming mode

Confirmations

These are the messages the I/O controller will send to the MCU, in response to the requests.

  • RESET_CFM (0x61) - Confirms the reset is in progress. A BOOTED_IND will be sent when the reset is complete.
  • PS2_DATA_CFM (0x62) - Keyboard and mouse data received since last previous PS2_DATA_CFM sent.
  • PS2_LED_CFM (0x63) - Confirm the keyboard LEDs have been set
  • LPT_DATA_CFM (0x64) - Sent when a byte has been written to the printer.
  • LPT_READ_CFM (0x65) - Returns the status bits:
    • Bit 0: nACK
    • Bit 1: BUSY
    • Bit 2: OUT_OF_PAPER
    • Bit 3: SELECT
    • Bit 4: nERROR
  • LPT_CTRL_CFM (0x66) - Sent when the control bytes have been written.
  • LPT_BUFFERED_DATA_CFM (0x67) - If status=0, buffered data has been stored, else there was an error (e.g. too much data).
  • LPT_READ_PEND_CFM (0x68) - A pend has been received.
  • LPT_SET_MODE_CFM (0x69) - Result of a mode configuration.
    • 0x00 - Mode successfully negotiated
    • Non-zero - An error occurred
  • PING_CFM (0x6A) - Empty response
  • BOOTLOADER_CFM (0x6B) - Entering firmware programming mode

Indications

These messages can be sent asynchronously by the I/O controller to the MCU.

  • BOOTED_IND (0x30) - Confirms the I/O controller is running and gives the keyboard and mouse status.
    • Bit 0 - 1 = Keyboard present, 0 = Keyboard missing
    • Bit 1 - 1 = Mouse present, 0 = Mouse missing
    • Bit 2:5 - 4-bit firmware version (v0..v15)
    • Bit 6 - Reserved (MCU should ignore)
    • Bit 7 - Always 1
  • PS2_DATA_IND (0x31) - Indicates that data is waiting to be read. Only sent once, until a PS2_DATA_REQ is seen.
  • LPT_BUFFER_EMPTY_IND (0x32) - Indicates that the LPT buffer is now empty and more bytes can be sent.
  • LPT_READ_PEND_IND (0x33) - The input pins matched the given levels.
  • BAD_COMMAND_IND (0x34) - Send when a bad request is received. That request will not receive a Confirmation.

Keyboard Data Format

The PS/2 Scan Code Set 2 is translated by the I/O controller into a basic code where each key is numbered 0..127. The top bit is then set for a key-up event and cleared for a key-down event. The 00 byte is a no-op. Only three key events can be sent every frame (i.e. at 60 Hz, or 180 key events per second or 90 keystrokes per second). I doubt anyone will need to type that fast on a Monotron.

  • F9: 0x01
  • AltRight: 0x02
  • F5: 0x03
  • F3: 0x04
  • F1: 0x05
  • F2: 0x06
  • F12: 0x07
  • ControlRight: 0x08
  • F10: 0x09
  • F8: 0x0A
  • F6: 0x0B
  • F4: 0x0C
  • Tab: 0x0D
  • BackTick: 0x0E
  • WindowsLeft: 0x0F
  • WindowsRight: 0x10
  • AltLeft: 0x11
  • ShiftLeft: 0x12
  • Menus: 0x13
  • ControlLeft: 0x14
  • Q: 0x15
  • Key1: 0x16
  • NumpadSlash: 0x17
  • NumpadEnter: 0x18
  • End: 0x19
  • Z: 0x1A
  • S: 0x1B
  • A: 0x1C
  • W: 0x1D
  • Key2: 0x1E
  • ArrowLeft: 0x1F
  • Home: 0x20
  • C: 0x21
  • X: 0x22
  • D: 0x23
  • E: 0x24
  • Key4: 0x25
  • Key3: 0x26
  • Insert: 0x27
  • Delete: 0x28
  • Spacebar: 0x29
  • V: 0x2A
  • F: 0x2B
  • T: 0x2C
  • R: 0x2D
  • Key5: 0x2E
  • ArrowDown: 0x2F
  • ArrowRight: 0x30
  • N: 0x31
  • B: 0x32
  • H: 0x33
  • G: 0x34
  • Y: 0x35
  • Key6: 0x36
  • ArrowUp: 0x37
  • PageDown: 0x38
  • PageUp: 0x39
  • M: 0x3A
  • J: 0x3B
  • U: 0x3C
  • Key7: 0x3D
  • Key8: 0x3E
  • Comma: 0x41
  • K: 0x42
  • I: 0x43
  • O: 0x44
  • Key0: 0x45
  • Key9: 0x46
  • Fullstop: 0x49
  • Slash: 0x4A
  • L: 0x4B
  • SemiColon: 0x4C
  • P: 0x4D
  • Minus: 0x4E
  • Quote: 0x52
  • BracketSquareLeft: 0x54
  • Equals: 0x55
  • CapsLock: 0x58
  • ShiftRight: 0x59
  • Enter: 0x5A
  • BracketSquareRight: 0x5B
  • BackSlash: 0x5D
  • Backspace: 0x66
  • Numpad1: 0x69
  • Numpad4: 0x6B
  • Numpad7: 0x6C
  • Numpad0: 0x70
  • NumpadPeriod: 0x71
  • Numpad2: 0x72
  • Numpad5: 0x73
  • Numpad6: 0x74
  • Numpad8: 0x75
  • Escape: 0x76
  • NumpadLock: 0x77
  • F11: 0x78
  • NumpadPlus: 0x79
  • Numpad3: 0x7A
  • NumpadMinus: 0x7B
  • NumpadStar: 0x7C
  • Numpad9: 0x7D
  • ScrollLock: 0x7E
  • F7: 0x7F

Mouse Data Format

This is as per the PS/2 specification, except that mutiple mouse packets (sent at 100 Hz) may be coalesced into a single message to the MCU (which only reads data at 60 Hz or less).

  • Status:
    • Bit 7 - Y overflow
    • Bit 6 - X overflow
    • Bit 5 - Y sign bit
    • Bit 4 - X sign bit
    • Bit 3 - Always 1
    • Bit 2 - Middle Button
    • Bit 1 - Right Button
    • Bit 0 - Left Button
  • X: Distance moved in the X direction since the last reading, in the range 0..255 (plus the sign bit above, so -255 to +255)
  • Y: Distance moved in the Y direction since the last reading. Values are per X above.

Licence

The code is Copyright (c) Jonathan 'theJPster' Pallant 2019. It is available under the Apache 2.0 or MIT licences, at your option.

The code in the third_party/avr_uart folder is under the following licence:

Copyright (C) 2012 Andy Gock

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.