With the controller configured, the driver must send specific commands to the mouse. Commands intended for the mouse are sent to the controller first via the 0xD4 prefix command.
int old_buttons = 0; while (1) mouse_y) printf("Mouse moved: %d, %d\n", mouse_x, mouse_y); mouse_x = 0; mouse_y = 0;
The driver processes this data and sends it to the operating system, which then uses it to update the mouse cursor position, perform actions, and execute commands. 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.
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); With the controller configured, the driver must send
The movement values are relative. To determine the actual delta movement, the driver must extract the sign bits from Byte 1 and construct 9-bit integers.
Developing a driver for a PS/2 mouse requires a distinct separation of concerns: the driver must first interface with the 8042 Super I/O controller (the keyboard controller) to enable the mouse channel, and subsequently interface directly with the mouse hardware to interpret movement and button state data. This paper outlines a driver model suitable for a monolithic kernel or embedded system where direct hardware access is permitted. The PS/2 mouse might seem like a relic
// Set controller configuration byte outb(0x64, 0x20); // Read command byte uint8_t config = inb(0x60); config |= 0x02; // Enable mouse IRQ12 (bit 1) config &= ~0x10; // Enable standard translation (optional) outb(0x64, 0x60); // Write command byte outb(0x60, config);
The mouse fires IRQ12 every time a byte is ready. We must read 3 bytes, then assemble the packet.