src/drivers/io.s

/*
 * raw port i/o primitives. nsc has no inline asm, so every driver that
 * touches a port (vga cursor, keyboard, pit, ata, pic) calls through
 * here via a plain extern declaration -- same proven pattern as the
 * nscc test suite's cross-file extern linking (t12).
 *
 * sysv abi: arg1 in %rdi, arg2 in %rsi. nsc does not promise the upper
 * bits of a register holding a narrower type (u8/u16) are clean, so
 * every function here reads only the sub-register width it needs
 * (%dil/%di/%sil) rather than trusting the rest of the word.
 */
.section .text
 
.global outb
.type outb, @function
outb:
	movw %di, %dx
	movb %sil, %al
	outb %al, %dx
	ret
 
.global inb
.type inb, @function
inb:
	movw %di, %dx
	inb %dx, %al
	movzbq %al, %rax
	ret
 
.global outw
.type outw, @function
outw:
	movw %di, %dx
	movw %si, %ax
	outw %ax, %dx
	ret
 
.global inw
.type inw, @function
inw:
	movw %di, %dx
	inw %dx, %ax
	movzwq %ax, %rax
	ret
 
/* classic "delay by writing to an unused port" trick, needed after
 * some port i/o sequences on real hardware (pic remap, ata) so the
 * device has time to react. harmless under qemu but keep it -- this
 * kernel should behave the same under emulation and on the user's
 * real hardware. */
.global io_wait
.type io_wait, @function
io_wait:
	xorb %al, %al
	movw $0x80, %dx
	outb %al, %dx
	ret
 
.global halt
.type halt, @function
halt:
	hlt
	ret
 
.global cli
.type cli, @function
cli:
	cli
	ret
 
.global sti
.type sti, @function
sti:
	sti
	ret