uart.c

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#include <core/system.h>
#include <core/string.h>
#include <console/earlycon.h>
#include <cpu/io.h>
#include <mm/mm.h>
 
static struct ioaddr earlycon_uart_ioaddr = {
    .addr = 0x3F8,
    .type = IOADDR_PORT,
};
 
#define UART_IER    1
#define UART_FCR    2
#define UART_LCR    3
#define UART_MCR    4
#define UART_DLL    0
#define UART_DLH    1
#define UART_LCR_DLAB    0x80

static void serial_init(void)
{
    io_out8(&earlycon_uart_ioaddr, UART_IER, 0x00);    /* no interrupts */
    io_out8(&earlycon_uart_ioaddr, UART_FCR, 0x00);    /* no FIFO */
    io_out8(&earlycon_uart_ioaddr, UART_LCR, 0x03);    /* 8 bits, no parity, one stop bit */
    io_out8(&earlycon_uart_ioaddr, UART_MCR, 0x03);    /* RTS and DTR */
 
    uint8_t lcr = io_in8(&earlycon_uart_ioaddr, UART_LCR);
    io_out8(&earlycon_uart_ioaddr, UART_LCR, lcr | UART_LCR_DLAB);  /* the divisor's registers */
    io_out8(&earlycon_uart_ioaddr, UART_DLL, 0x03);    /* divisor 3: 38400 baud (low byte) */
    io_out8(&earlycon_uart_ioaddr, UART_DLH, 0x00);    /* (high byte) */
    io_out8(&earlycon_uart_ioaddr, UART_LCR, lcr & ~UART_LCR_DLAB); /* back to the data registers */
}

static int serial_tx_empty(void)
{
    return io_in8(&earlycon_uart_ioaddr, 5) & 0x20;
}

static int serial_chr(char chr)
{
    if (chr == '\n')
        serial_chr('\r');
 
    for (int i = 0; i < 100000 && !serial_tx_empty(); ++i)
        ;
 
    io_out8(&earlycon_uart_ioaddr, 0, chr);
 
    return 1;
}

static int serial_str(char *str)
{
    int ret = 0;
 
    while (*str)
        ret += serial_chr(*str++);
 
    return ret;
}
 
static int earlycon_uart_puts(char *s)
{
    return serial_str(s);
}
 
static int earlycon_uart_putc(char c)
{
    return serial_chr(c);
}
 
static void earlycon_uart_init(void)
{
    serial_init();
 
    /* there's probably a terminal at the other end: reset its attributes */
    serial_str("\033[0m");
}
 
struct earlycon earlycon_uart = {
    .init = earlycon_uart_init,
    .putc = earlycon_uart_putc,
    .puts = earlycon_uart_puts,
};