BasicKernel/kernel/ports.c

unsigned char port_byte_in(unsigned short port) {
	unsigned char res;
	/*
	 * `"=a" (res)' means: put result of `al' into `res' variable
	 * `"d" (port)' means: load `port' into `dx'.
	 */
	__asm__("in %%dx, %%al" : "=a" (res) : "d" (port));
	return res;
}

void port_byte_out(unsigned short port, unsigned char data) {
	__asm__("out %%al, %%dx" : : "a" (data), "d" (port));
}

unsigned short port_word_in(unsigned short port) {
	unsigned short res;
	__asm__("in %%dx, %%ax" : "=a" (res) : "d" (port));
	return res;
}

void port_word_out(unsigned short port, unsigned short data) {
	__asm__("out %%ax, %%dx" : : "a" (data), "d" (port));
}