This PR intends to provide firmware OTA capability via Arduino IoT Cloud and MKR MEM shield connected to either MR 1000, MR WiFi 1010, MR NB 1500 or MR GSM 1400. The following modifications need to be made to the sketch:

/* ... */
#include <SFU.h>
#include <utility/ota/OTAStorage_MKRMEM.h>
/* ... */
static OTAStorage_MKRMEM ota_storage;
/* ... */
void setup()
{
  /* ... */
  ArduinoCloud.setOTAStorage(ota_storage);
}

Furthermore the desired OTA storage type needs to be configured in ArduinoIoTCloud_Config.h, e.g.

#ifndef OTA_STORAGE_MKRMEM
  #define OTA_STORAGE_MKRMEM      (1)
#endif

The firmware sets the hidden int property OTA_STORAGE_TYPE to one of the following values which allows the cloud to determine which OTA update storage medium is available:

• OTA_STORAGE_TYPE = -1 -> No OTA storage medium connected, OTA not possible
• OTA_STORAGE_TYPE = 0 -> MKR MEM Shield connected, OTA possible

If the OTA update file has been downloaded and its checksum verified successfully then a reset is performed and the new firmware is flashed onto the MCU by the second stage SFU bootloader. In case of an error during the update process no reset is performed and the source of the error is written to the hidden int property OTA_ERROR. The following error codes are available:

• OTA_ERROR = 0 -> No Error
• OTA_ERROR = 1 -> OTA storage initialisation failed
• OTA_ERROR = 2 -> OTA storage open failed
• OTA_ERROR = 3 -> OTA storage write failed
• OTA_ERROR = 4 -> Checksum mismatch
• OTA_ERROR = 5 -> Received data overrun (too much data received before it could be processed)