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#include "ports.h"
/**
* Read a byte from the specified port
*/
uint8_t port_byte_in (uint16_t port) {
uint8_t 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 (uint16_t port, uint8_t 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));
}
uint16_t port_word_in (uint16_t port) {
uint16_t result;
asm("in %%dx, %%ax" : "=a" (result) : "d" (port));
return result;
}
void port_word_out (uint16_t port, uint16_t data) {
asm volatile("out %%ax, %%dx" : : "a" (data), "d" (port));
}