minix/kernel/arch/earm/omap_serial.c

#include <assert.h>
#include <sys/types.h>
#include <machine/cpu.h>
#include <minix/type.h>
#include <io.h>
#include "omap_serial.h"

struct omap_serial {
	vir_bytes base;		
};

static struct omap_serial omap_serial = {
	.base = 0,
};

/* 
 * In kernel serial for the omap. The serial driver like most other
 * drivers needs to be started early and even before the MMU is turned on.
 * We start by directly accessing the hardware memory address. Later on
 * a when the MMU is turned on we still use a 1:1 mapping for these addresses.
 *
 * Pretty soon we are going to remap these addresses at later stage. And this
 * requires us to use a dynamic base address. The idea is to receive a callback
 * from VM with the new address to use.
 *
 * We also anticipate on the beaglebone port an try to keep the differences between
 * the drivers to a minimum by initializing a struct here and not using (to much) 
 * constants in the code.
 *
 * The serial driver also gets used in the "pre_init" stage before the kernel is loaded
 * in high memory so keep in mind there are two copies of this code in the kernel.
 */
void omap3_ser_init(){
#ifdef DM37XX
	omap_serial.base = OMAP3_DM37XX_DEBUG_UART_BASE;
#endif
#ifdef AM335X
	omap_serial.base = OMAP3_AM335X_DEBUG_UART_BASE;
#endif
    assert(omap_serial.base);
}

void omap3_ser_putc(char c)
{
    assert(omap_serial.base);

    int i;

    /* Wait until FIFO's empty */
    for (i = 0; i < 100000; i++)
	if (mmio_read(omap_serial.base +  OMAP3_LSR) & OMAP3_LSR_THRE)
	    break;

    /* Write character */
    mmio_write(omap_serial.base + OMAP3_THR, c);

    /* And wait again until FIFO's empty to prevent TTY from overwriting */
    for (i = 0; i < 100000; i++)
	if (mmio_read(omap_serial.base + OMAP3_LSR) & (OMAP3_LSR_THRE | OMAP3_LSR_TEMT))
	    break;
}