add new sketch for RTC running in MIX mode with Alarm

This examples is configuring the RTC in MIX mode
(binary + calendar BCD) and set Alarm B (if exists)
few ticks after the current time, whenAlarm A is set
in calendar mode. Mainly used on stm32wl55 devices.

Author: FRASTM

examples/mixRTCAlarm/mixRTCAlarm.ino

@@ -0,0 +1,99 @@
+/*
+  mixRTCAlarm
+
+  This sketch shows how to configure the RTC alarm in MIX mode
+
+  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 <STM32RTC.h>
+
+/* Get the rtc object */
+STM32RTC& rtc = STM32RTC::getInstance();
+
+/* 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 timenow;
+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.setRTCMode(STM32RTC::MODE_MIX);
+#endif /* RTC_BINARY_NONE */
+  rtc.begin(false); // initialize RTC 24H format
+
+  rtc.setTime(hours, minutes, seconds);
+  rtc.setDate(day, month, year);
+
+  rtc.attachInterrupt(alarmAMatch, STM32RTC::ALARM_A);
+#ifdef RTC_ALARM_B
+  rtc.attachInterrupt(alarmBMatch, STM32RTC::ALARM_B);
+#endif /* RTC_ALARM_B */
+
+  /* wait for a while */
+  for (uint32_t i = 0 ; i < 0x8ffff ; i++);
+
+  timenow = rtc.getSubSeconds();
+  Serial.printf("start at subsec = %d\r\n", timenow);
+
+  /* program Alarm A in calendar mode + 5 seconds */
+  rtc.setAlarmDay(day, STM32RTC::ALARM_A);
+  rtc.setAlarmTime(hours, minutes, seconds + 5, STM32RTC::ALARM_A);
+  rtc.enableAlarm(rtc.MATCH_DHHMMSS, STM32RTC::ALARM_A);
+
+  Serial.printf("set Alarm A \r\n");
+
+#ifdef RTC_ALARM_B
+  /* program Alarm B at timeout + ms from now */
+  timeout = timenow + 300;  /* for ex. 4096 (0x1000) is 16 seconds with a fqce_APRE*/
+
+  rtc.setAlarmSubSeconds(timeout, STM32RTC::ALARM_B);
+  rtc.enableAlarm(rtc.MATCH_SUBSEC, STM32RTC::ALARM_B);
+
+  Serial.printf("set Alarm B at = %d\r\n", timeout);
+#endif /* RTC_ALARM_B */
+
+}
+
+void loop()
+{
+
+}
+
+void alarmAMatch(void *data)
+{
+  UNUSED(data);
+  Serial.printf("Alarm A Match! at subsec = %d\r\n", rtc.getSubSeconds());
+}
+
+#ifdef RTC_ALARM_B
+void alarmBMatch(void *data)
+{
+  UNUSED(data);
+  Serial.printf("Alarm B Match! at subsec = %d\r\n", rtc.getSubSeconds()); 
+}
+#endif /* RTC_ALARM_B */
+