circuitpython/stm/rtc.c

#include <stdio.h>
#include <stm32f4xx.h>

#include "misc.h"
#include "mpconfig.h"
#include "qstr.h"
#include "obj.h"
#include "rtc.h"

void rtc_init(void) {
    /* Enable the PWR clock */
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_PWR, ENABLE);

    /* Allow access to RTC */
    PWR_BackupAccessCmd(ENABLE);

    if (RTC_ReadBackupRegister(RTC_BKP_DR0) == 0x32F2) {
        // RTC still alive, so don't re-init it
        // wait for RTC APB register synchronisation
        RTC_WaitForSynchro();
        return;
    }

    uint32_t timeout = 10000000;

    /* Enable the PWR clock */
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_PWR, ENABLE);

    /* Allow access to RTC */
    PWR_BackupAccessCmd(ENABLE);

    /* Enable the LSE OSC */
    RCC_LSEConfig(RCC_LSE_ON);

    /* Wait till LSE is ready */
    while((RCC_GetFlagStatus(RCC_FLAG_LSERDY) == RESET) && (--timeout > 0)) {
    }

    /* If LSE timed out, use LSI instead */
    if (timeout == 0) {
        // Disable the LSE OSC
        RCC_LSEConfig(RCC_LSE_OFF);

        // Enable the LSI OSC
        RCC_LSICmd(ENABLE);

        /* Wait till LSI is ready */
        while(RCC_GetFlagStatus(RCC_FLAG_LSIRDY) == RESET) {
        }

        /* Use LSI as the RTC Clock Source */
        RCC_RTCCLKConfig(RCC_RTCCLKSource_LSI);
    } else {
        /* Use LSE as the RTC Clock Source */
        RCC_RTCCLKConfig(RCC_RTCCLKSource_LSE);
    }

    /* Note: LSI is around (32KHz), these dividers should work either way */
    /* ck_spre(1Hz) = RTCCLK(LSE) /(uwAsynchPrediv + 1)*(uwSynchPrediv + 1)*/
    uint32_t uwSynchPrediv = 0xFF;
    uint32_t uwAsynchPrediv = 0x7F;

    /* Enable the RTC Clock */
    RCC_RTCCLKCmd(ENABLE);

    /* Wait for RTC APB registers synchronisation */
    RTC_WaitForSynchro();

    /* Configure the RTC data register and RTC prescaler */
    RTC_InitTypeDef RTC_InitStructure;
    RTC_InitStructure.RTC_AsynchPrediv = uwAsynchPrediv;
    RTC_InitStructure.RTC_SynchPrediv = uwSynchPrediv;
    RTC_InitStructure.RTC_HourFormat = RTC_HourFormat_24;
    RTC_Init(&RTC_InitStructure);

    // Set the date (BCD)
    RTC_DateTypeDef RTC_DateStructure;
    RTC_DateStructure.RTC_Year = 0x13;
    RTC_DateStructure.RTC_Month = RTC_Month_October;
    RTC_DateStructure.RTC_Date = 0x26;
    RTC_DateStructure.RTC_WeekDay = RTC_Weekday_Saturday;
    RTC_SetDate(RTC_Format_BCD, &RTC_DateStructure);

    // Set the time (BCD)
    RTC_TimeTypeDef RTC_TimeStructure;
    RTC_TimeStructure.RTC_H12     = RTC_H12_AM;
    RTC_TimeStructure.RTC_Hours   = 0x01;
    RTC_TimeStructure.RTC_Minutes = 0x53;
    RTC_TimeStructure.RTC_Seconds = 0x00;
    RTC_SetTime(RTC_Format_BCD, &RTC_TimeStructure);

    // Indicator for the RTC configuration
    RTC_WriteBackupRegister(RTC_BKP_DR0, 0x32F2);
}

/******************************************************************************/
/* Micro Python bindings                                                      */

mp_obj_t pyb_rtc_read(void) {
    RTC_TimeTypeDef RTC_TimeStructure;
    RTC_GetTime(RTC_Format_BIN, &RTC_TimeStructure);
    printf("%02d:%02d:%02d\n", RTC_TimeStructure.RTC_Hours, RTC_TimeStructure.RTC_Minutes, RTC_TimeStructure.RTC_Seconds);
    return mp_const_none;
}