max80_fw/fw/rtc.c

/*
 * Read/write DS3231M RTC
 */

#include "fw.h"
#include "console.h"
#include "io.h"

static inline uint32_t i2c_wait(void)
{
    uint32_t rdata;

    while ((rdata = I2C_RDATA) & I2C_BUSY)
	pause();

    return rdata;
}

static void i2c_send(uint8_t byte, uint8_t ctl)
{
    i2c_wait();

    I2C_WDATA = (byte << 8) | I2C_NAK | ctl;
}

static bool i2c_acked(void)
{
    return !(i2c_wait() & I2C_NAK);
}

static int i2c_recv(uint8_t ctl)
{
    uint32_t rdata;
    
    i2c_wait();

    I2C_WDATA = (~0xff) | ctl;

    rdata = i2c_wait();
    return rdata >> 8;
}

#define RTC_REGS 19
#define RTC_ADDR 0x68
#define RTC_WCMD ((RTC_ADDR << 1)+0)
#define RTC_RCMD ((RTC_ADDR << 1)+1)

void read_rtc(void)
{
    uint8_t rtc_regs[RTC_REGS];
    int i;
    
    i2c_set_speed(400);
    
    /* Synchronize I2C */
    i2c_send(0xff, I2C_P);
    
    i2c_send(RTC_WCMD, 0);

    if (!i2c_acked()) {
	con_printf("No RTC detected at I2C address 0x%02x\n", RTC_ADDR);
	i2c_send(0xff, I2C_P);
	return;
    }
    
    i2c_send(0, I2C_SR);
    i2c_send(RTC_RCMD, 0);

    con_printf("RTC register content:\n");
    for (i = 0; i < RTC_REGS-1; i++) {
	rtc_regs[i] = i2c_recv(0);
	con_printf("%02x ", rtc_regs[i]);
    }

    rtc_regs[i] = i2c_recv(I2C_NAK | I2C_P);
    con_printf("%02x\n", rtc_regs[i]);
}