STM32duinoLoraWan new example going to sleep and sending packet

Modifying the basic.ino to add sleeping period
After LoraWan is connected, it periodically goes to sleep
and send a packet on device wakeUp

Signed-off-by: Francois Ramu <francois.ramu@st.com>

Author: FRASTM

examples/LowPowerLoraWan/LowPowerLoraWan.ino

@@ -0,0 +1,136 @@
+/**
+ * This is an example that demonstrates how to configure the
+ * library, join the network, send regular packets and print any
+ * downlink packets received when the lowpower mode is enabled.
+ * This example is using the RTC in MIX (binary and BCD) mode
+ * and the lowPower mode to set an Alarm (ALARM_A) before going to sleep
+ * When alarm Wakes up the system, it send a packet over the LoraWan
+ *
+ * Revised BSD License - https://spdx.org/licenses/BSD-3-Clause.html
+ */
+#include <STM32LoRaWAN.h>
+#include <STM32LowPower.h>
+#include <STM32RTC.h>
+
+STM32LoRaWAN modem;
+extern STM32RTC rtc;
+
+char payload[27]; /* packet to be sent */
+
+bool connected = false; /* LoraWan connection ready */
+
+/* Change this value to set alarm match offset in millisecond */
+static uint32_t atime = 4000;
+
+// Declare it volatile since it's incremented inside an interrupt
+volatile int alarmMatch_counter = 0;
+
+void setup() {
+  pinMode(LED_BUILTIN, OUTPUT);
+
+  Serial.begin(115200);
+  Serial.println("Start");
+  modem.begin(EU868);
+
+  /* rtc is already init'd in MIX mode by the LoraWan */
+  rtc.setTime(21, 51, 20);
+  rtc.setDate(2, 3, 4, 5);
+
+  // Configure join method by (un)commenting the right method
+  // call, and fill in credentials in that method call.
+  connected = modem.joinOTAA(/* AppEui */ "0000000000000000", /* AppKey */ "00000000000000000000000000000000", /* DevEui */ "0000000000000000");
+  //connected = modem.joinABP(/* DevAddr */ "00000000", /* NwkSKey */ "00000000000000000000000000000000", /* AppSKey */ "00000000000000000000000000000000");
+
+  if (connected) {
+    Serial.println("Joined");
+  } else {
+    Serial.println("Join failed");
+    while (true) /* infinite loop */;
+  }
+
+  // Configure low power
+  LowPower.begin();
+  LowPower.enableWakeupFrom(&rtc, alarmMatch, &atime);
+
+  // Configure first alarm in 6 second then it will be done in the rtc callback
+  rtc.setAlarmEpoch(rtc.getEpoch() + 6);
+}
+
+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();
+  
+  /* Alarm has matched 2 times before reching this point */
+  if (connected) {
+  	send_packet();
+  } else {
+  	Serial.printf("Alarm at %02d:%02d:%02d\r\n",
+          rtc.getHours(), rtc.getMinutes(), rtc.getSeconds());
+  }
+}
+
+void send_packet()
+{
+  /* prepare the Tx packet : get date and format string */
+  sprintf((char *)payload, "%02d/%02d/%04d - %02d:%02d:%02d",
+          rtc.getMonth(), rtc.getDay(), 2000 + rtc.getYear(),
+          rtc.getHours(), rtc.getMinutes(), rtc.getSeconds());
+
+  modem.setPort(10);
+  modem.beginPacket();
+  modem.write(payload, sizeof(payload));
+  if (modem.endPacket() == sizeof(payload)) {
+    Serial.println("Sent packet");
+  } else {
+    Serial.println("Failed to send packet");
+  }
+
+  if (modem.available()) {
+    Serial.print("Received packet on port ");
+    Serial.print(modem.getDownlinkPort());
+    Serial.print(":");
+    while (modem.available()) {
+      uint8_t b = modem.read();
+      Serial.print(" ");
+      Serial.print(b >> 4, HEX);
+      Serial.print(b & 0xF, HEX);
+    }
+    Serial.println();
+  }
+}
+
+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 epoc_ms;
+  uint32_t sec = 0;
+  uint32_t _millis = 1000;
+
+  if (data != NULL) {
+    _millis = *(uint32_t*)data;
+  }
+
+  sec = _millis / 1000;
+
+  _millis = _millis % 1000;
+  epoc = rtc.getEpoch(&epoc_ms);
+
+  //Update epoch_ms - might need to add a second to epoch
+  epoc_ms += _millis;
+  if (epoc_ms >= 1000) {
+    sec ++;
+    epoc_ms -= 1000;
+  }
+  alarmMatch_counter++;
+  // set the alarm again
+  rtc.setAlarmEpoch(epoc + sec, STM32RTC::MATCH_SS, epoc_ms);
+}