Merge pull request #7875 from thinkyhead/bf2_fill_eeprom_dat_ff

[2.0.x] Update LPC persistent store to initialize eeprom.dat with FF

Marlin/src/HAL/HAL_LPC1768/persistent_store_impl.cpp

@@ -19,14 +19,31 @@ FATFS fat_fs;
 FIL eeprom_file;
 
 bool access_start() {
+  UINT file_size = 0,
+       bytes_written = 0;
+  const char eeprom_zero = 0xFF;
   MSC_Aquire_Lock();
-  if(f_mount(&fat_fs, "", 1)){
+  if (f_mount(&fat_fs, "", 1)) {
     MSC_Release_Lock();
     return false;
   }
   FRESULT res = f_open(&eeprom_file, "eeprom.dat", FA_OPEN_ALWAYS | FA_WRITE | FA_READ);
-  if(res) MSC_Release_Lock();
-  return (res == FR_OK);
+  if (res) MSC_Release_Lock();
+
+  if (res == FR_OK) file_size = f_size(&eeprom_file);
+
+  if (res == FR_OK) {
+    f_lseek(&eeprom_file, file_size);
+    while (file_size < E2END && res == FR_OK) {
+      res = f_write(&eeprom_file, &eeprom_zero, 1, &bytes_written);
+      file_size++;
+    }
+  }
+  if (res == FR_OK) {
+    f_lseek(&eeprom_file, 0);
+    f_sync(&eeprom_file);
+  }
+  return res == FR_OK;
 }
 
 bool access_finish() {