Intro Link to heading

While making a Zephyr tutorial, I bricked the board I was working on. I’m planning on releasing that guide soon. Before that I wanted to share the details on what hardware I bricked, what I used to fix it, and how I did it.

Hardware Link to heading

MCU Dev board: Sparkfun SAMD21 Dev Breakout SoC Debug device: Jeff Probe, which is an open source variant of the black magic debugger, but much cheaper ~$15 vs ~$85

Board Picture
Sparkfun SAMD21 Dev Board Sparkfun SAMD21 Dev Board\|300
Jeff Probe Debugger Jeff Probe\|300

🟡 You may need to solder the jtag header on the devboard. Some flux and an okay iron works well. You need 2x5, 1.27mm Pitch breakout pins.

Install Link to heading

You need to install arm-none-eabi toolchain to build the bootloader and run gdb:

# Arch
pacman -S arm-none-eabi-gdb arm-none-eabi-gcc arm-none-eabi-newlib

# Ubuntu
apt install gcc-arm-none-eabi newlib-arm-none-eabi gdb-multiarch

Clone Link to heading

Clone and build the bootloader source code:

git clone https://github.com/adafruit/uf2-samdx1
cd uf2-samdx1
make BOARD=sparkfun-samd21-dev
# output file build/sparkfun-samd21-dev/bootloader-sparkfun-samd21-dev-v3.16.0-19-g4365018.elf

Flash Link to heading

To flash the board, first follow these steps to prepare the board to be flashed:

  1. Connect JTAG cable from probe to dev board.
  2. Connect microusb to probe from PC (take note of what /dev/ttyACM<number> it enumerates as. Two will usually show up, use the lower one. To be really sure, run sudo dmesg -W to follow the kernel logs when you plug it in, it should show which devices are enumerated.
  3. Connect microusb to dev board from PC
  4. Edit a file gdbinit and put the following contents in:
target extended-remote /dev/ttyACM<num> # check in dmesg
monitor swdp_scan # make sure this works too, cable could be upside down
attach 1
load
  1. Run gdb with your gdbinit script:
sudo arm-none-eabi-gdb bootloader-sparkfun-samd21-dev-v3.16.0-19-g4365018.elf -x gdbinit
# You don't need sudo if you put yourself in the right group
  1. Unplug the probe and hard reset the dev board. Double tapping the reset button should put it back into bootloader mode.

🔴 If something went wrong during the GDB step, the most likely error is your jtag cable is upside down, verify that the output of the monitor swdp_scan shows a successful probe of the dev board

References Link to heading

Other board guide