forked from cfenollosa/os-tutorial
-
Notifications
You must be signed in to change notification settings - Fork 0
Expand file tree
/
Copy pathports.c
More file actions
37 lines (33 loc) · 1.13 KB
/
ports.c
File metadata and controls
37 lines (33 loc) · 1.13 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
#include "ports.h"
/**
* Read a byte from the specified port
*/
u8 port_byte_in (u16 port) {
u8 result;
/* Inline assembler syntax
* !! Notice how the source and destination registers are switched from NASM !!
*
* '"=a" (result)'; set '=' the C variable '(result)' to the value of register e'a'x
* '"d" (port)': map the C variable '(port)' into e'd'x register
*
* Inputs and outputs are separated by colons
*/
__asm__("in %%dx, %%al" : "=a" (result) : "d" (port));
return result;
}
void port_byte_out (u16 port, u8 data) {
/* Notice how here both registers are mapped to C variables and
* nothing is returned, thus, no equals '=' in the asm syntax
* However we see a comma since there are two variables in the input area
* and none in the 'return' area
*/
__asm__ __volatile__("out %%al, %%dx" : : "a" (data), "d" (port));
}
u16 port_word_in (u16 port) {
u16 result;
__asm__("in %%dx, %%ax" : "=a" (result) : "d" (port));
return result;
}
void port_word_out (u16 port, u16 data) {
__asm__ __volatile__("out %%ax, %%dx" : : "a" (data), "d" (port));
}