Overview

The input subsystem handles all human-interface device input: PS/2 keyboard (IRQ1) and PS/2 mouse (IRQ12). Both are routed through the 8042 PS/2 controller. Port I/O primitives live in input/port.rs and are used throughout the kernel.

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().

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

PS/2 keyboard
  → IRQ1 → keyboard_handler (idt.rs)
      → keyboard::push_scancode(sc)     → SCANCODE_BUF  (shell)
      → irq::Subscriber::push_irq(sc)   → RECEPTORS[0..5] (userland subscribers)

PS/2 mouse
  → IRQ12 → mouse_handler (idt.rs)
      → mouse::push_byte(b)
          → reassemble 3-byte packet
          → MouseSubscriber::push(pkt)  → MOUSE_RECEPTORS[0..5] (userland subscribers)

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
`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

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.