k-chow/k/serial.c

#include <stddef.h>

#include "serial.h"
#include "io.h"

static void set_baud_rate(void)
{
    u8 line_control_register = inb(COM1 + 3);
    outb(COM1 + 3, DLAB | line_control_register);
    outb(COM1, 3);
    outb(COM1 + 1, 0);
    outb(COM1 + 3, line_control_register);
}

void init_serial(void)
{
    set_baud_rate();

    outb(COM1 + 3, NO_PARITY | EIGHT_BITS_LENGTH);
    outb(COM1 + 2, FIFO | TRIGGER_LVL_14 | CLEAR_TRANSMIT_FIFO
            | CLEAR_RECEIVE_FIFO);
    outb(COM1 + 1, ENABLE_TRANSMITTER);
}

int write(const char *buf, size_t count)
{
    size_t sent;

    for(sent = 0; sent < count; ++sent)
    {
        u8 line_status = inb(COM1 + 5);
        if (!(line_status & EMPTY_TRANSMITTER))
            break;
        outb(COM1, buf[sent]);
    }

    return sent;
}