Make your own OS in 30 days – day7/8: Mouse interrupt handler

Day 7/8 implements FIFO ring buffer for Keyboard/Mouse handler to handle more than 1 byte code.
The main function wait for interrupt until it gets an interrupt by STI and HLT. When it’s interrupted, it disables interrupts by CLI, get key/mouse data by STI, draw it and wait for the next interrupt.

This version doesn’t have layers and mouse cursor overwrites background as below.

struct FIFO8 mousefifo;

struct FIFO8 {
	unsigned char *buf;
	int p, q, size, free, flags;
};

void inthandler21(int *esp)
{
	unsigned char data;
	io_out8(PIC0_OCW2, 0x61);	// IRQ-01 accepted -> PIC0
	data = io_in8(PORT_KEYDAT);
	fifo8_put(&keyfifo, data);
	return;
}


void inthandler2c(int *esp)
{
	unsigned char data;
	io_out8(PIC1_OCW2, 0x64);	// IRQ-12 accepted -> PIC1
	io_out8(PIC0_OCW2, 0x62);	// IRQ-02 accepted -> PIC0
	data = io_in8(PORT_KEYDAT);
	fifo8_put(&mousefifo, data);
	return;
}

int fifo8_put(struct FIFO8 *fifo, unsigned char data)
{
	if (fifo->free == 0) {
		fifo->flags |= FLAGS_OVERRUN;
		return -1;
	}
	fifo->buf[fifo->p] = data;
	fifo->p++;
	if (fifo->p == fifo->size) {
		fifo->p = 0;
	}
	fifo->free--;
	return 0;
}

// loop in the main function
	for (;;) {
		io_cli();
		if (fifo8_status(&keyfifo) + fifo8_status(&mousefifo) == 0) {
			io_stihlt();
		} else {
			if (fifo8_status(&keyfifo) != 0) {
				i = fifo8_get(&keyfifo);
				io_sti();
				// draw key data
			} else if (fifo8_status(&mousefifo) != 0) {
				i = fifo8_get(&mousefifo);
				io_sti();
				// draw mouse data
				}
			}
		}
	}