new example to configure RTC alarm in MIX mode and wakeup the system

examples/mixRTCAlarmSleep/mixRTCAlarmSleep.ino

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+/*
+  mixRTCAlarmSleep
+
+  This sketch shows how to configure the RTC alarm in MIX mode and go to sleep
+
+  Creation 12 Dec 2017
+  by Wi6Labs
+  Modified 03 Jul 2020
+  by Frederic Pillon for STMicroelectronics
+  Modified 03 Jul 2023
+  by Francois Ramu for STMicroelectronics
+
+  This example code is in the public domain.
+
+  https://github.com/stm32duino/STM32RTC
+*/
+
+#include "STM32LowPower.h"
+#include <STM32RTC.h>
+
+/* Get the rtc object */
+STM32RTC& rtc = STM32RTC::getInstance();
+
+/* Change this value to set alarm match offset */
+/* Note that STM32F1xx does not manage subsecond only second */
+static uint32_t atime = 148; /* in MIX mode, this is 148 ticks * 3.9ms/tick = 578 ms */
+
+// Declare it volatile since it's incremented inside an interrupt
+volatile int alarmMatch_counter = 0;
+
+/* Change these values to set the current initial time */
+const byte seconds = 05;
+const byte minutes = 14;
+const byte hours = 16;
+
+/* Change these values to set the current initial date */
+const byte day = 25;
+const byte month = 9;
+const byte year = 15;
+
+uint32_t timeout;
+
+void setup()
+{
+  Serial.begin(115200);
+
+  // Select RTC clock source: LSI_CLOCK, LSE_CLOCK or HSE_CLOCK.
+  // By default the LSI is selected as source : choose LSE
+  rtc.setClockSource(STM32RTC::LSE_CLOCK);
+#if defined(RTC_BINARY_NONE)
+  rtc.setBinaryMode(STM32RTC::MODE_MIX);
+  rtc.begin(true); /* reset the RTC else the binary mode is not changed */
+#else
+  rtc.begin();
+#endif /* RTC_BINARY_NONE */
+  // Configure low power
+  LowPower.begin();
+
+  rtc.setTime(hours, minutes, seconds);
+  rtc.setDate(day, month, year);
+
+  /* wait for a while */
+  delay(200);
+
+  pinMode(LED_BUILTIN, OUTPUT);
+
+  LowPower.enableWakeupFrom(&rtc, alarmMatch, &atime);
+  rtc.disableAlarm(STM32RTC::ALARM_A);
+  /* program Alarm in mix mode
+   * Configure first alarm in 2 second : 2000ms is 512 ticks 
+   * then it will be done in the rtc callback
+   */
+  timeout = rtc.getSubSeconds() + 512;
+
+  rtc.setAlarmSubSeconds(timeout, STM32RTC::ALARM_A);
+  rtc.enableAlarm(rtc.MATCH_SUBSEC, STM32RTC::ALARM_A);
+
+  Serial.printf("set Alarm at = %d\r\n", timeout);
+
+}
+
+void loop()
+{
+  Serial.print("Alarm Match: ");
+  Serial.print(alarmMatch_counter);
+  Serial.println(" times.");
+  Serial.flush();
+  digitalWrite(LED_BUILTIN, HIGH);
+  LowPower.deepSleep();
+  digitalWrite(LED_BUILTIN, LOW);
+  LowPower.deepSleep();
+}
+
+
+void alarmMatch(void *data)
+{
+  // This function will be called once on device wakeup
+  // You can do some little operations here (like changing variables which will be used in the loop)
+  // Remember to avoid calling delay() and long running functions since this functions executes in interrupt context
+  uint32_t epoc;
+  uint32_t _millis = 1000;
+
+  if (data != NULL) {
+    _millis = *(uint32_t*)data;
+  }
+
+#ifdef STM32F1xx
+  uint32_t epoc_ms;
+  uint32_t sec = 0;
+
+  sec = _millis / 1000;
+  // Minimum is 1 second
+  if (sec == 0) {
+    sec = 1;
+  }
+  epoc = rtc.getEpoch(&epoc_ms);
+#else
+  epoc = rtc.getSubSeconds() + _millis; //in ms
+#endif
+  alarmMatch_counter++;
+  rtc.setAlarmSubSeconds(epoc, STM32RTC::ALARM_A);
+}
+