IDT (Interrupts)

The interrupt descriptor table

Interrupts are kind of a tool for getting the CPU's attention. This can either be because of a serious fault in the system or because something like a timer needs to tick or a PS2 mouse wants attention.

There are two sections to interrupts, a manager and a handler.

Manager

This is where we initialise the interrupts with a default handler and tell the system to start accepting these interrupts.

The system requires a table of descriptors which look like this:

struct gate_descriptor_t{
	uint16_t base_low;
	uint16_t sel;
	uint8_t ist;
	uint8_t flags;
	uint16_t base_med;
	uint32_t base_high;
	uint32_t null;
} __attribute__((packed));

We use packed to tell the compiler not to move any of the definition around (which would save memory but cause issues)

And we tell the system to size and position of the table with:

struct idt_pointer_t
{
	uint16_t limit;
	uint64_t base;
} __attribute__((packed));

These will point to a assembly created code that configures register and stack variables before proceeding back to C++ for the handling of the interrupt.

Handler

All this needs to be a basic function that takes two arguments, a data argument (For the interrupts that require one) and a register argument that holds the stack of the previous process pre interrupt.