Update RTC memory example

libraries/esp8266/examples/RTCUserMemory/RTCUserMemory.ino

@@ -1,52 +1,106 @@
-// Example: Storing struct data in RTC user memory
+// Example: Storing struct data in RTC user rtcDataory
 //
-// Struct data with the maximum size of 512 bytes can be stored in the RTC user memory using the ESP-specifc APIs.
-// The stored data can be retained between deep sleep cycles. However, the data might be lost after power cycling the ESP8266.
+// Struct data with the maximum size of 512 bytes can be stored
+// in the RTC user rtcDataory using the ESP-specifc APIs.
+// The stored data can be retained between deep sleep cycles.
+// However, the data might be lost after power cycling the ESP8266.
+//
+// This example uses deep sleep mode, so connect GPIO16 and RST
+// pins before running it.
 //
 // Created Mar 30, 2016 by Macro Yau.
 //
 // This example code is in the public domain.
 
-typedef struct {
-  byte data[512];
-} rtcUserMemory;
+// CRC function used to ensure data validity
+uint32_t calculateCRC32(const uint8_t *data, size_t length);
 
-rtcUserMemory mem;
+// helper function to dump memory contents as hex
+void printMemory();
 
-void printMemory(bool readFromRtc) {
-  char buf[3];
-  Serial.print(readFromRtc ? "Read:  " : "Write: ");
-  for (int i = 0; i < sizeof(mem); i++) {
-    sprintf(buf, "%02X", mem.data[i]);
-    Serial.print(buf);
-    Serial.print(" ");
-  }
-  Serial.println();
-}
+// Structure which will be stored in RTC memory.
+// First field is CRC32, which is calculated based on the
+// rest of structure contents.
+// Any fields can go after CRC32.
+// We use byte array as an example.
+struct {
+  uint32_t crc32;
+  byte data[508];
+} rtcData;
 
 void setup() {
   Serial.begin(115200);
   Serial.println();
+  delay(1000);
 
-  // Read struct from RTC user memory
-  if (ESP.rtcUserMemoryRead((uint32_t*) &mem, sizeof(mem))) {
-    printMemory(true);
+  // Read struct from RTC memory
+  if (ESP.rtcUserMemoryRead(0, (uint32_t*) &rtcData, sizeof(rtcData))) {
+    Serial.println("Read: ");
+    printMemory();
+    Serial.println();
+    uint32_t crcOfData = calculateCRC32(((uint8_t*) &rtcData) + 4, sizeof(rtcData) - 4);
+    Serial.print("CRC32 of data: ");
+    Serial.println(crcOfData, HEX);
+    Serial.print("CRC32 read from RTC: ");
+    Serial.println(rtcData.crc32, HEX);
+    if (crcOfData != rtcData.crc32) {
+      Serial.println("CRC32 in RTC memory doesn't match CRC32 of data. Data is probably invalid!");
+    }
+    else {
+      Serial.println("CRC32 check ok, data is probably valid.");
+    }
   }
 
   // Generate new data set for the struct
-  for (int i = 0; i < sizeof(mem); i++) {
-    mem.data[i] = random(0, 128);
+  for (int i = 0; i < sizeof(rtcData); i++) {
+    rtcData.data[i] = random(0, 128);
+  }
+  // Update CRC32 of data
+  rtcData.crc32 = calculateCRC32(((uint8_t*) &rtcData) + 4, sizeof(rtcData) - 4);
+  // Write struct to RTC memory
+  if (ESP.rtcUserMemoryWrite(0, (uint32_t*) &rtcData, sizeof(rtcData))) {
+    Serial.println("Write: ");
+    printMemory();
+    Serial.println();
   }
 
-  // Write struct to RTC user memory
-  if (ESP.rtcUserMemoryWrite((uint32_t*) &mem, sizeof(mem))) {
-    printMemory(false);
-  }
-  
-  // Enter deep sleep mode for 10 seconds
-  ESP.deepSleep(10e6);
+  Serial.println("Going into deep sleep for 5 seconds");
+  ESP.deepSleep(5e6);
 }
 
 void loop() {
-  
+}
+
+uint32_t calculateCRC32(const uint8_t *data, size_t length)
+{
+  uint32_t crc = 0xffffffff;
+  while (length--) {
+    uint8_t c = *data++;
+    for (uint32_t i = 0x80; i > 0; i >>= 1) {
+      bool bit = crc & 0x80000000;
+      if (c & i) {
+        bit = !bit;
+      }
+      crc <<= 1;
+      if (bit) {
+        crc ^= 0x04c11db7;
+      }
+    }
+  }
+  return crc;
+}
+
+void printMemory() {
+  char buf[3];
+  for (int i = 0; i < sizeof(rtcData); i++) {
+    sprintf(buf, "%02X", rtcData.data[i]);
+    Serial.print(buf);
+    if ((i + 1) % 32 == 0) {
+      Serial.println();
+    }
+    else {
+      Serial.print(" ");
+    }
+  }
+  Serial.println();
 }