File content as of revision 189:f392fc9709a3:

/* mbed Microcontroller Library
 * Copyright (c) 2018 GigaDevice Semiconductor Inc.
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#if DEVICE_RTC

#include "rtc_api.h"

static uint8_t rtc_init_flag = 0;

/** Initialize the RTC peripheral
 *
 * Powerup the RTC in perpetration for access. This function must be called
 * before any other RTC functions ares called. This does not change the state
 * of the RTC. It just enables access to it.
 *
 * @note This function is safe to call repeatedly - Tested by ::rtc_init_test
 */
void rtc_init(void)
{
    /* make sure RTC only init once */
    if (rtc_init_flag) {
        return;
    }
    rtc_init_flag = 1;

    /* enable PMU and BKPI clocks */
    rcu_periph_clock_enable(RCU_BKPI);
    rcu_periph_clock_enable(RCU_PMU);
    /* allow access to BKP domain */
    pmu_backup_write_enable();
    /* enable LXTAL */
    rcu_osci_on(RCU_LXTAL);
    /* wait till LXTAL is ready */
    rcu_osci_stab_wait(RCU_LXTAL);
    /* select RCU_LXTAL as RTC clock source */
    rcu_rtc_clock_config(RCU_RTCSRC_LXTAL);
    /* enable RTC Clock */
    rcu_periph_clock_enable(RCU_RTC);
    /* wait for RTC registers synchronization */
    rtc_register_sync_wait();
    /* wait until last write operation on RTC registers has finished */
    rtc_lwoff_wait();
    /* set RTC prescaler: set RTC period to 1s */
    rtc_prescaler_set(32767);
    /* wait until last write operation on RTC registers has finished */
    rtc_lwoff_wait();
}

/** Deinitialize RTC
 *
 * Powerdown the RTC in preparation for sleep, powerdown or reset. That should only
 * affect the CPU domain and not the time keeping logic.
 * After this function is called no other RTC functions should be called
 * except for ::rtc_init.
 */
void rtc_free(void)
{
}

/** Check if the RTC has the time set and is counting
 *
 * @retval 0 The time reported by the RTC is not valid
 * @retval 1 The time has been set the RTC is counting
 */
int rtc_isenabled(void)
{
    if (RESET == (RTC_CTL & RTC_CTL_RSYNF)) {
        return 0;
    } else {
        return 1;
    }
}

/** Get the current time from the RTC peripheral
 *
 * @return The current time in seconds
 *
 * @note Some RTCs are not synchronized with the main clock. If
 * this is the case with your RTC then you must read the RTC time
 * in a loop to prevent reading the wrong time due to a glitch.
 * The test ::rtc_glitch_test is intended to catch this bug.
 */
time_t rtc_read(void)
{
    return (rtc_counter_get());
}

/** Write the current time in seconds to the RTC peripheral
 *
 * @param t The current time to be set in seconds.
 */
void rtc_write(time_t t)
{
    rtc_counter_set((uint32_t)t);
    rtc_lwoff_wait();
}

#endif /* DEVICE_RTC */