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Input Overview

The input subsystem handles PS/2 keyboards (IRQ1), PS/2 mice (IRQ12), and USB HID boot keyboards on xHCI controllers. PS/2 devices use the 8042 controller; USB keyboards use a native driver polled from the timer interrupt. Both keyboard paths deliver Set 1 scancodes to the shell and existing userland subscribers. Port I/O primitives live in input/port.rs.

IRQ Wiring

IRQ IDT vector Handler Source
IRQ1 0x21 keyboard_handler PS/2 keyboard via 8042 port 0x60
IRQ12 0x2C mouse_handler PS/2 auxiliary port via 8042 port 0x60

Both are registered in abi/idt.rs by install_isrs().

USB input uses IRQ0's scheduler timer to poll the xHCI event ring, before the scheduler acquires its lock. It does not require an xHCI interrupt handler. See USB keyboard support.

The 8042 controller shares a single data register (port 0x60) between keyboard and mouse. The status register (port 0x64) bit 5 distinguishes the source: 0 = keyboard, 1 = mouse.

Data Flow

Keyboard IRQ1 fans out to the kernel shell and keyboard subscriber rings; mouse IRQ12 builds packets for mouse subscriber rings; user applications poll both input pipes.

Keyboard scancodes and mouse packets use separate subscriber buffers. Reading those buffers through syscall 0x03 is non-blocking.

Modules

Module File Purpose
keyboard input/keyboard.rs Scancode buffer, shell loop, scancode→ASCII, tab completion
irq input/irq.rs Keyboard fan-out to up to 5 userland subscribers
xhci usb/xhci.rs Controller ownership, DMA rings, USB enumeration and keyboard polling
hid usb/hid.rs HID boot reports, Set 1 translation and held-key repeat
mouse input/mouse.rs PS/2 mouse init, packet reassembly, subscriber ring buffers
port input/port.rs Raw x86 I/O port primitives (IN/OUT for u8/u16/u32)
cmd input/cmd.rs Shell built-in command dispatcher
elf input/elf.rs ELF loader (run_elf) called by shell and syscall 0x2A
elf_path input/elf_path.rs Validate bare names and explicit absolute executable paths

PIC Configuration

The 8259A PIC is set up so that hardware IRQs are remapped to IDT vectors 0x20–0x2F (master 0x20–0x27, slave 0x28–0x2F):

  • IRQ1 (keyboard) → 0x21 (master)
  • IRQ12 (mouse) → 0x2C (slave, cascade through IRQ2)

The mouse init sequence (mouse::init) explicitly unmasks IRQ2 on the master PIC (0x21 &= ~0x04) and IRQ12 on the slave PIC (0xA1 &= ~0x10). Without these two clears, IRQ12 is permanently masked.

Port I/O Primitives (input/port.rs)

All hardware access goes through these wrappers around the IN/OUT x86 instructions:

Function Width Instruction
read_u8(port) 8-bit IN AL, DX
write_u8(port, v) 8-bit OUT DX, AL
read_u16(port) 16-bit IN AX, DX
write_u16(port, v) 16-bit OUT DX, AX
read_u32(port) 32-bit IN EAX, DX
write_u32(port, v) 32-bit OUT DX, EAX

read and write are aliases for the u8 variants and are used throughout the codebase.

Userland accesses port I/O through syscalls 0x30 (write) and 0x31 (read), which call these functions indirectly.

Related documentation: Kernel Internals, Keyboard, Mouse, Input Syscalls.