Add functions and example to read reset reason from RTC backup register 8

libraries/STM32H747_System/examples/STM32H747_getResetReason/STM32H747_getResetReason.ino

@@ -0,0 +1,44 @@
+#include "STM32H747_System.h"
+
+void setup() {  
+  Serial.begin(115200);
+  while (!Serial) {}
+
+  reset_reason_t resetReason = STM32H747::getResetReason();
+  Serial.println(getString(resetReason));
+}
+
+String getString(reset_reason_t val) {
+  switch (val){
+  case RESET_REASON_POWER_ON:
+    return "Reset Reason Power ON";
+  case RESET_REASON_PIN_RESET:
+    return "Reset Reason PIN Reset";
+  case RESET_REASON_BROWN_OUT:
+    return "Reset Reason Brown Out";
+  case RESET_REASON_SOFTWARE:
+    return "Reset Reason Software";
+  case RESET_REASON_WATCHDOG:
+    return "Reset Reason Watchdog";
+  case RESET_REASON_LOCKUP:
+    return "Reset Reason Lockup";
+  case RESET_REASON_WAKE_LOW_POWER:
+    return "Reset Reason Wake Low Power";
+  case RESET_REASON_ACCESS_ERROR:
+    return "Reset Reason Access Error";
+  case RESET_REASON_BOOT_ERROR:
+    return "Reset Reason Boot Error";
+  case RESET_REASON_MULTIPLE:
+    return "Reset Reason Multiple";
+  case RESET_REASON_PLATFORM:
+    return "Reset Reason Platform";
+  case RESET_REASON_UNKNOWN:
+    return "Reset Reason Unknown";
+  default:
+    return "N/A";
+  }
+}
+
+void loop() {  
+  delay(1000);
+}

libraries/STM32H747_System/src/Portenta_System.h

@@ -12,6 +12,7 @@ class Portenta_System: public STM32H747
   Portenta_System() {};
   virtual bool begin();
   virtual bool enterLowPower();
+
   String getBoardRevision();
   uint16_t getCarrierSpecs();
 };

libraries/STM32H747_System/src/STM32H747_System.cpp

@@ -1,9 +1,10 @@
 #include "STM32H747_System.h"
 #include "Wire.h"
-#include "mbed.h"
 
 #define PMIC_ADDRESS 0x08
 
+extern RTC_HandleTypeDef RTCHandle;
+
 uint8_t STM32H747::readReg(uint8_t subAddress) {
   char response = 0xFF;
   Wire1.beginTransmission(PMIC_ADDRESS);
@@ -23,6 +24,18 @@ void STM32H747::setRegister(uint8_t reg, uint8_t val) {
   Wire1.endTransmission();
 }
 
+uint32_t STM32H747::readBackupRegister(RTCBackup reg) {
+  return HAL_RTCEx_BKUPRead(&RTCHandle, (uint32_t)reg);
+}
+
+void STM32H747::writeBackupRegister(RTCBackup reg, uint32_t data) {
+  HAL_RTCEx_BKUPWrite(&RTCHandle, (uint32_t)reg, data);
+}
+
+reset_reason_t STM32H747::getResetReason() {
+  return (reset_reason_t)readBackupRegister(RTCBackup::DR8);
+}
+
 /*
  * This function disables the external oscillators and use the HSI instead.
  * If lowspeed = true : f = 100MHz

libraries/STM32H747_System/src/STM32H747_System.h

@@ -2,12 +2,51 @@
 #define H747_System_h_
 
 #include "Arduino.h"
+#include "mbed.h"
+
+enum class RTCBackup {
+  DR0,      /* RESERVED Arduino Magic */
+  DR1,      /* RESERVED OTA storage type */
+  DR2,      /* RESERVED OTA offset */
+  DR3,      /* RESERVED OTA update size */
+  DR4,      /* RESERVED MCUboot scratch storage type */
+  DR5,      /* RESERVED MCUboot scratch offset */
+  DR6,      /* RESERVED MCUboot scratch size */
+  DR7,      /* RESERVED MCUboot debug */
+  DR8,      /* RESERVED Reset reason */
+  DR9,
+  DR10,
+  DR11,
+  DR12,
+  DR13,
+  DR14,
+  DR15,
+  DR16,
+  DR17,
+  DR18,
+  DR19,
+  DR20,
+  DR21,
+  DR22,
+  DR23,
+  DR24,
+  DR25,
+  DR26,
+  DR27,
+  DR28,
+  DR29,
+  DR30,
+  DR31,
+};
 
 class STM32H747 {
 
 public:
   virtual bool begin() = 0;
   virtual bool enterLowPower() = 0;
+  static reset_reason_t  getResetReason();
+  static uint32_t readBackupRegister(RTCBackup register);
+  static void writeBackupRegister(RTCBackup register, uint32_t data);
 
 protected:
   uint8_t readReg(uint8_t subAddress);