uart.c

// Intel 8250 serial port (UART).

#include "types.h"
#include "defs.h"
#include "param.h"
#include "traps.h"
#include "spinlock.h"
#include "fs.h"
#include "file.h"
#include "mmu.h"
#include "proc.h"
#include "x86.h"

#define COM1    0x3f8

static int uart;    // is there a uart?

void
uartinit(void) {
    char *p;

    // Turn off the FIFO
    outb(COM1 + 2, 0);

    // 9600 baud, 8 data bits, 1 stop bit, parity off.
    outb(COM1 + 3, 0x80);    // Unlock divisor
    outb(COM1 + 0, 115200 / 9600);
    outb(COM1 + 1, 0);
    outb(COM1 + 3, 0x03);    // Lock divisor, 8 data bits.
    outb(COM1 + 4, 0);
    outb(COM1 + 1, 0x01);    // Enable receive interrupts.

    // If status is 0xFF, no serial port.
    if (inb(COM1 + 5) == 0xFF)
        return;
    uart = 1;

    // Acknowledge pre-existing interrupt conditions;
    // enable interrupts.
    inb(COM1 + 2);
    inb(COM1 + 0);
    picenable(IRQ_COM1);
    ioapicenable(IRQ_COM1, 0);

    // Announce that we're here.
    for (p = "xv6...\n"; *p; p++)
        uartputc(*p);
}

void
uartputc(int c) {
    int i;

    if (!uart)
        return;
    for (i = 0; i < 128 && !(inb(COM1 + 5) & 0x20); i++)
        microdelay(10);
    outb(COM1 + 0, c);
}

static int
uartgetc(void) {
    if (!uart)
        return -1;
    if (!(inb(COM1 + 5) & 0x01))
        return -1;
    return inb(COM1 + 0);
}

void
uartintr(void) {
    consoleintr(uartgetc);
}