ref: 8b8814e4df3e370608da903e6cdb96ba33aacdad
dir: /pc/com.c/
#include <u.h>
#include <libc.h>
#include <x86.h>
/* see https://en.wikibooks.org/wiki/Serial_Programming/8250_UART_Programming
--- UART Registers
Address DLAB I/O Access Register Name
+0 0 W Transmitter Holding Buffer
+0 0 R Receiver Buffer
+0 1 R/W Divisor Latch Low Byte
+1 0 R/W Interrupt Enable Register
+1 1 R/W Divisor Latch High Byte
+2 x R Interrupt Identification Register
+2 x W FIFO Control Register
+3 x R/W Line Control Register
+4 x R/W Modem Control Register
+5 x R Line Status Register
+6 x R Modem Status Register
+7 x R/W Scratch Register
*/
void
com_init(uint16 port, uint32 baud_rate)
{
uint16 divisor = 115200 / baud_rate;
outb(port + 2, 0); /* Turn off the FIFO */
outb(port + 3, 0x80); /* set the divisor latch access bit (7th bit)*/
outb(port + 0, divisor & 0xff);
outb(port + 1, divisor >> 8);
outb(port + 3, 0x3); /* lock the divisor and select 8 data bits */
outb(port + 4, 0x0);
/* testing */
outb(port + 4, 0x1e); /* set in loopback mode*/
outb(port + 0, 0xee); /* write some random data in it */
if (inb(port + 0) != 0xee) {
/* the serial is faulty */
/* TODO panic */
return;
}
/* the serial is working correctly, set in normal operation mode */
outb(port + 4, 0x0F);
}
void
com_putchar(uint16 port, uint8 c)
{
while(!(inb(port + 5) & 0x20))
{
; /* wait for uart to be ready */
}
outb(port, c);
}
void
com_putc(char c)
{
com_putchar(COM1, c);
}
void
com_puts(char* s)
{
for(int i = 0 ; i < strlen(s) ; i++)
com_putc(s[i]);
}
char
com_getchar(uint16 port)
{
while(!(inb(port + 5) & 1))
; /* wait til data is ready */
return inb(port);
}
char
com_getc(void)
{
return com_getchar(COM1);
}