I am trying to perform a firmware update from an SD card, on a Sodaq Sara AFF board. If i use the SDU.h library in my sketch, it fails the board check. See this link please.

I have edited the SDU.cpp myself to force the selection of ARDUINO_SAM_ZERO. It is now :

__attribute__ ((section(".sketch_boot")))
unsigned char sduBoot[0x6000] = {
  #include "boot/mzero.h"

I have increased the size to 6000 otherwise it was complaining too many initializers.

I also have changed the SD_SS_PIN to match my pin on the SDUboot.ino, under extras. Afterwards, i recompiled it with build.sh in the same folder.

But I am unable to perform the firmware update. After power cycling the board (original code: the blink example, target update: blink with a faster rate) - the original firmware remains.

I exported the firmware using arduino IDE -> export compiled bynary, and tested both versions with and without bootloader.

Any help would be appreciated.

  • 3
    what bootloader has the board? the difference between MKR/Zero and M0 is for SDU the bootloader size which is 2kB for MKR and Zero and 4 kB for M0. why do you want to use SDU? is your sketch larger then half of the flash?
    – Juraj
    Commented Jan 26, 2021 at 6:41
  • @Juraj the board has a ATSAMD21J18, 32-Bit ARM Cortex M0+. So, I assume 4 kB bootloader size. Is it relevant if the sketch is larger then half of the flash?
    – phlegx
    Commented Mar 30, 2021 at 12:25
  • Zero and M0 are both SAMD21 but have different bootloaders. the sketch binary doesn't have to be smaller then half of the flash if it is loaded from SD card
    – Juraj
    Commented Mar 30, 2021 at 13:03
  • github.com/arduino/ArduinoCore-samd/pull/344/commits
    – Juraj
    Commented Apr 2, 2021 at 6:24
  • And what does it mean finally? What is the correct setup to get it work?
    – phlegx
    Commented Apr 7, 2021 at 0:04

1 Answer 1



I have compiled my own SDUBoot.ino with fixed SDU_START 0x2000 and for SODAQ Sara (boot/sodaq_sara.h). My sketch with #include "SDU.h" compiles successfully. The board package is also installed in Arduino (http://downloads.sodaq.net/package_sodaq_samd_index.json). Here my code with changes (base is SodaqCore-samd-1.8.6-sodaq from Github):

File libraries/SDU/extras/SDUBoot/SDUBoot.ino:

#include <SD.h>
#include <FlashStorage.h>

#define SDU_START    0x2000
#define SDU_SIZE     0x4000

#define SKETCH_START (uint32_t*)(SDU_START + SDU_SIZE)

#define SDCARD_SS_PIN 10


FlashClass flash;

// Initialize C library
extern "C" void __libc_init_array(void);

int main() {



  if (SD.begin(SDCARD_SS_PIN) && SD.exists(UPDATE_FILE)) {
    File updateFile = SD.open(UPDATE_FILE);
    uint32_t updateSize = updateFile.size();
    bool updateFlashed = false;

    if (updateSize > SDU_SIZE) {
      // skip the SDU section
      updateSize -= SDU_SIZE;

      uint32_t flashAddress = (uint32_t)SKETCH_START;

      // erase the pages
      flash.erase((void*)flashAddress, updateSize);

      uint8_t buffer[512];

      // write the pages
      for (uint32_t i = 0; i < updateSize; i += sizeof(buffer)) {
        updateFile.read(buffer, sizeof(buffer));

        flash.write((void*)flashAddress, buffer, sizeof(buffer));

        flashAddress += sizeof(buffer);

      updateFlashed = true;


    if (updateFlashed) {

  // jump to the sketch

  //Reset vector table address

  // address of Reset_Handler is written by the linker at the beginning of the .text section (see linker script)
  uint32_t resetHandlerAddress = (uint32_t) * (SKETCH_START + 1);
  // jump to reset handler
  asm("bx %0"::"r"(resetHandlerAddress));

File libraries/SDU/extras/SDUBoot/build.sh:

#!/bin/sh -x


if [[ "$OSTYPE" == "darwin"* ]]; then

buildSDUBootSketch() {

    $ARDUINO --verify --board $BOARD --preserve-temp-files --pref build.path="$BUILD_PATH" $SKETCH
    cat "$BUILD_PATH/$SKETCH_NAME.bin" | xxd -i > $DESTINATION
    rm -rf "$BUILD_PATH"

mkdir -p "$OUTPUT_PATH"

buildSDUBootSketch "SODAQ:samd:sodaq_sara" "$OUTPUT_PATH/sodaq_sara.h"

File libraries/SDU/src/SDU.cpp:

#include <Arduino.h>

#include "SDU.h"

__attribute__ ((section(".sketch_boot")))
unsigned char sduBoot[0x4000] = {
  #include "boot/sodaq_sara.h"

Sketch file sdu_test.ino:

#include <Arduino.h>
#include "SDU.h"

#define DEBUG_STREAM SerialUSB
#error "Please select the SODAQ SARA as your board"

#define DEBUG_STREAM_BAUD 115200

String message;

void setup() {
  // Start communication.

  while (!DEBUG_STREAM) {
    // Wait for Serial Monitor to be opened.

  message += "Sketch compile date and time: ";
  message += __DATE__;
  message += " ";
  message += __TIME__;

  // print out the sketch compile date and time on the serial port

void loop() {
  // add you own code here

File arduino/50/.arduino15/packages/SODAQ/hardware/samd/1.8.6/variants/sodaq_sara/linker_scripts/gcc/flash_with_bootloader.ld add these lines:


. = ALIGN(0x2000);


    PROVIDE(__sodaq_firmware_state = ORIGIN(FLASH) - 0x100);

    .text :
        __text_start__ = .;


        . = ALIGN(0x2000);

On SD card (formatted as FAT32) I have stored the renamed file UPDATE.bin without bootloader of the compiled sketch file. Pin D10 is connected and used as chip select CS.

Build boot hex files:

$ cd libraries/SDU/extras/SDUBoot
$ ./build.sh

Version 1.8.6-sodaq has these missing lines on arduino_zero variant but not on sodaq_sara variant.

  • Hi, I was away due to things changing in Cororna times, but now I'm back. This does not work. It compiles, but I am unable to load the new firmware without bootloader.
    – Sean
    Commented Jul 24, 2021 at 16:29

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