Arduino Zero (SAMD21G18) seems to program but won't run

Like others here I’m trying to replace the Arduino IDE with for better development of libraries and particularly so I can debug. I’m working with an Arduino Zero (this one) with the built-in EDBG debug chip.

In case it’s relevant, I also spent some time (unsuccessfully) trying to get Atmel Studio 7 to program this Arduino. In the process I seemed to blow away the bootloader. I used the Arduino IDE to re-burn the bootloader.

I’m testing with the ubiquitous blink program.

#include "Arduino.h"

void setup() {

void loop() {
  digitalWrite(LED_BUILTIN, HIGH); 
  digitalWrite(LED_BUILTIN, LOW);

From the Arduino IDE, I can successfully upload and run the sketch as expected (after removing the first #include line)

However, when I switch over to, I get the following when I build and run.

[Mon Aug  7 13:03:02 2017] Processing zero (platform: atmelsam; board: zero; framework: arduino)
Verbose mode can be enabled via `-v, --verbose` option
Collected 7 compatible libraries
Looking for dependencies...
Project does not have dependencies
Linking .pioenvs/zero/firmware.elf

Checking program size
text       data     bss     dec     hex filename
9448        256    1780   11484    2cdc .pioenvs/zero/firmware.elf
Uploading .pioenvs/zero/firmware.bin
GNU MCU Eclipse 64-bits Open On-Chip Debugger 0.10.0+dev-00135-g80299198 (2017-06-22-18:37)
Licensed under GNU GPL v2
For bug reports, read
Info : auto-selecting first available session transport "swd". To override use 'transport select <transport>'.
none separate
adapter speed: 400 kHz
cortex_m reset_config sysresetreq
Info : CMSIS-DAP: SWD  Supported
Info : CMSIS-DAP: Interface Initialised (SWD)
Info : CMSIS-DAP: FW Version = 03.22.01B3
Info : SWCLK/TCK = 1 SWDIO/TMS = 1 TDI = 1 TDO = 1 nTRST = 0 nRESET = 1
Info : CMSIS-DAP: Interface ready
Info : clock speed 400 kHz
Info : SWD DPIDR 0x0bc11477
Info : at91samd21g18.cpu: hardware has 4 breakpoints, 2 watchpoints
target halted due to debug-request, current mode: Thread
xPSR: 0x81000000 pc: 0x00000614 msp: 0x20007ffc
** Programming Started **
auto erase enabled
Info : SAMD MCU: SAMD21G18A (256KB Flash, 32KB RAM)
Warn : Adding extra erase range, 00000000 to 0x00001fff
wrote 24576 bytes from file .pioenvs/zero/firmware.bin in 2.411482s (9.952 KiB/s)
** Programming Finished **
** Verify Started **
verified 9704 bytes in 0.820003s (11.557 KiB/s)
** Verified OK **
** Resetting Target **
**Error: at91samd21g18.cpu -- clearing lockup after double fault**
target halted due to debug-request, current mode: Handler HardFault
xPSR: 0x61000003 pc: 0xfffffffe msp: 0xffffffd8
shutdown command invoked
========================= [SUCCESS] Took 5.14 seconds =========================
  • Despite the “Success” message, the sketch does not run (as expected with the Error line showing the lockup after double fault.

Also not sure why there is the line “Info : at91samd21g18.cpu: hardware has 4 breakpoints, 2 watchpoints”. Could these have been added by Atmel Studio and not removed? I’ve unsuccessfully tried to run the debugger but didn’t get anywhere near adding breakpoints.

Furthermore, if I go back to the Arduino IDE and try to Upload the sketch it reports the same lockup/double fault error, and I cannot proceed until I re-burn the bootloader.

Happy to provide any further log dumps as needed to diagnose.

Thanks for any help.

Just worked out that the line

Info : at91samd21g18.cpu: hardware has 4 breakpoints, 2 watchpoints
just means that that processor’s M0 core hardware is capable of 4 breakpoints, 2 watchpoints.

However, I’m still wondering what I’ve done wrong to stop my program from starting. Do I have debugging enabled incorrectly somewhere in

Please file an issue here Issues · platformio/platform-atmelsam · GitHub

@robroyaus Did you ever find out what was wrong? Having the same problem.