Ps/2 Compatible Mouse Driver [upd] -

// Send EOI to PIC outb(0x20, 0x20); In real mode or protected mode, you must set up the IDT (Interrupt Descriptor Table) for IRQ12 (vector 0x2C if PIC is in standard remap). Example for 32-bit protected mode:

int old_buttons = 0; while (1) if (mouse_buttons != old_buttons) printf("Buttons: %s %s %s\n", (mouse_buttons & 1) ? "Left" : " ", (mouse_buttons & 2) ? "Right" : " ", (mouse_buttons & 4) ? "Middle" : " "); old_buttons = mouse_buttons; if (mouse_x Enabling Scroll Wheel (IntelliMouse) Send this sequence to switch to 4-byte packets: ps/2 compatible mouse driver

The PS/2 mouse might seem like a relic of the 1990s, but it remains the gold standard for low-level OS development. Unlike USB, which relies on complex host controllers and descriptor parsing, the PS/2 interface is simple, memory-mapped, and interrupt-driven. In this article, we’ll build a bare-bones PS/2 mouse driver from scratch, covering initialization, packet decoding, and integration with a simple GUI. 1. Understanding the PS/2 Interface The PS/2 port uses two bidirectional lines: Clock (usually IRQ 12 for the mouse) and Data . Communication is synchronous, with the device sending 11-bit packets (1 start bit, 8 data bits, 1 parity bit, 1 stop bit) when the host pulls the clock low. // Send EOI to PIC outb(0x20, 0x20); In

uint8_t data = inb(0x60);

void install_mouse_handler() set_idt_gate(0x2C, (uint32_t)mouse_isr, 0x08, 0x8E); outb(0x21, inb(0x21) & ~0x20); // Unmask IRQ12 on slave PIC outb(0xA1, inb(0xA1) & ~0x20); "Right" : " ", (mouse_buttons & 4)

if (mouse_cycle == 0) // Byte 0: verify bit 3 = 1 (always set in standard packet) if ((data & 0x08) == 0x08) mouse_packet[0] = data; mouse_cycle = 1; else if (mouse_cycle == 1) mouse_packet[1] = data; mouse_cycle = 2; else if (mouse_cycle == 2) = 0xFFFFFF00; mouse_x += dx; mouse_y -= dy; // Invert Y for screen coordinates mouse_buttons = mouse_packet[0] & 0x07;

Next steps: Add absolute positioning (tablet mode), dynamic rate switching, or hook the driver into a windowing system. Happy coding! Did this article help you? Share your PS/2 driver war stories in the comments below.