8042 microcontroller integration for x86

@author: Mitran Andrei

1) Things I must follow

• Define and implement register abstractions for ports 0x60 (data) and 0x64 (status/command)
• Implement a polled input function (no interrupts) to read PS/2 scan codes
• Decode and display keyboard input characters
• Test driver functionality in QEMU
• Keyboard + Mouse driver

2) Documentation

Assign symbols to each reference:

• § https://wiki.osdev.org/index.php?title=I8042_PS/2_Controller&utm_source=chatgpt.com
• $ https://www.dosdays.co.uk/media/intel/Intel%208042.pdf
• & https://os.phil-opp.com/
• ! https://book.tockos.org/development/peripheral.html
• @ https://book.tockos.org/development/hil.html
• % https://github.com/rust-embedded-community/pc-keyboard
• ^ https://github.com/rust-embedded-community/pc-keyboard/blob/main/src/lib.rs
• ~ https://github.com/Halicery/8042/blob/main/8042_PS2_INTERN.TEXT

Another useful link:

• https://github.com/torvalds/linux/blob/master/drivers/input/serio/libps2.c
  • We use this to research detection of every keyboard

Gathered Information:

• I/O Ports: Uses ports 0x60 (data) and 0x64 (status/command) [§]
• Controller Overview: Intel 8042 supports bi-directional keyboard (IRQ1) and mouse (IRQ12) channels on x86 [§]
• Translation Mode: Default translates scan-code set 2 → set 1; disable to receive raw sets 2/3 [§]
• USB Legacy Support: BIOS may emulate PS/2 over USB—disable emulation before PS/2 init [§]

Status Register (0x64 read)

The Status Register flags (bit = offset):

• Bit 0 – Output buffer status (0 = empty, 1 = full)
• Bit 1 – Input buffer status (0 = empty, 1 = full)
• Bit 2 – System Flag (POST passed)
• Bit 3 – Command/data (0 = data, 1 = command)
• Bit 4 – Unknown (chipset-specific)
• Bit 5 – Unknown (chipset-specific)
• Bit 6 – Time-out error (0 = no error, 1 = timeout)
• Bit 7 – Parity error (0 = no error, 1 = parity)

Defined as:

Status [
    OBFull     OFFSET(0) NUMBITS(1) [],  // bit 0
    IBFull     OFFSET(1) NUMBITS(1) [],  // bit 1
    SysFlag    OFFSET(2) NUMBITS(1) [],  // bit 2
    CmdData    OFFSET(3) NUMBITS(1) [],  // bit 3
    TimeoutErr OFFSET(6) NUMBITS(1) [],  // bit 6
    ParityErr  OFFSET(7) NUMBITS(1) [],  // bit 7
]

3) Commands

Command Byte	Meaning	Response Byte
0x20	Read “byte 0” from internal RAM	Controller Configuration Byte
0x21–0x3F	Read “byte N” (N = cmd & 0x1F) from internal RAM	Unknown
0x60	Write next byte to “byte 0” of internal RAM (Config Byte)	None
0x61–0x7F	Write next byte to “byte N” of internal RAM	None
0xA7	Disable second PS/2 port (if supported)	None
0xA8	Enable second PS/2 port (if supported)	None
0xA9	Test second PS/2 port (if supported)	0x00 = pass
0xAA	Test PS/2 Controller	0x55 = pass, 0xFC = fail
0xAB	Test first PS/2 port	0x00 = pass
0xAC	Diagnostic dump (read all internal RAM)	Unknown
0xAD	Disable first PS/2 port	None
0xAE	Enable first PS/2 port	None
0xC0	Read controller input port	Unknown
0xC1	Copy bits 0–3 of input port → status bits 4–7	None
0xC2	Copy bits 4–7 of input port → status bits 4–7	None
0xD0	Read Controller Output Port	Unknown
0xD1	Write next byte to Controller Output Port	None
0xD2	Write next byte to first PS/2 port output buffer (emulate input)	None
0xD3	Write next byte to second PS/2 port output buffer (emulate input)	None
0xD4	Write next byte to second PS/2 port input buffer (sends to device)	None
0xF0–0xFF	Pulse output lines low for 6 ms (mask bits 0–3; bit 0 = reset line)	None

Bits marked “only if dual-port supported” should be treated as undefined on single-port controllers.

4) Configuration Byte (0x20/0x60)

Read/Write via commands 0x20 and 0x60:

Bit	Name	Meaning
0	First PS/2 IRQ Enable	1 = keyboard IRQ enabled; 0 = disabled
1	Second PS/2 IRQ Enable	1 = mouse IRQ enabled; 0 = disabled*
2	System Flag	1 = POST passed; 0 = invalid
3	Reserved	Must be 0
4	First PS/2 Clock	1 = disabled; 0 = enabled
5	Second PS/2 Clock	1 = disabled; 0 = enabled*
6	Translation Enable	1 = translate SC2→SC1; 0 = raw codes
7	Reserved	Must be 0

Config [
    Intr1Enable   OFFSET(0) NUMBITS(1) [],
    Intr2Enable   OFFSET(1) NUMBITS(1) [],
    SysFlag       OFFSET(2) NUMBITS(1) [],
    Reserved3     OFFSET(3) NUMBITS(1) [],
    Disable1Clock OFFSET(4) NUMBITS(1) [],
    Disable2Clock OFFSET(5) NUMBITS(1) [],
    Translation   OFFSET(6) NUMBITS(1) [],
    Reserved7     OFFSET(7) NUMBITS(1) [],
]

*only if dual-port supported

5) Detecting PS/2 Devices

Full detection sequence:

1. Send Disable Scanning (0xF5) → await ACK (0xFA)
2. Send Identify (0xF2) → await ACK (0xFA)
3. Read up to 2 ID bytes (timeout if only one)
4. Send Enable Scanning (0xF4)

Partial ID responses:

• none → Ancient AT keyboard
• 0x00 → Standard PS/2 mouse
• 0x03 → Scroll-wheel mouse
• 0x04 → 5-button mouse
• 0xAB, 0x83 → MF2 keyboard
• … (see Linux libps2.c for full list)

6) Next Steps

• Driver struct and init sequence
• Implement keyboard driver
• Mouse driver