SAMD21 Programming Notes

Explorations into how to program SAMD21 chips like those in Trinket M0, Arduino Zero, etc.

Eventual goal: Build a crystalless SAMD21-based board and program it with a combined bin of a UF2 bootloader and my own program.

One preliminary idea is:

Steps to get there using existing SAMD21 board (e.g. Trinket M0, FemtoUSB):

Reprogram bootloader using UF2
Program chip with an Arduino sketches using uf2
Talk to chip w/ GDB using JTAG programmer (JLink via commandline, no Atmel Studio)
Reprogram bootloader with JTAG programmer (JLink via commandline, no Atmel Studio)
Program chip with Arduino sketch using JTAG programmer

Progress so far...

Reprogram bootloader via UF2 - Trinket M0

Double-click button on Trinket M0 to get into UF2 bootloader

LED will heartbeat
Trinket M0 shows up as "TRINKETBOOT" disk

Create new UF2 bootloader

git clone https://github.com/Microsoft/uf2-samd21/
cd uf2-samd21
make BOARD=trinket

Copy resulting file update-bootloader.uf2 to disk
Tada, new bootloader installed
Edit file boards/trinket/board_config.h to change bootloader id strings

Program Arduino sketch with UF2 - Trinket M0

Create sketch as normal
Open build tmp directory and copy out .bin file
Use uf2-samd21 'bin2uf2.js' script to convert to uf2:

node uf2-samd21/scripts/bin2uf2.js sketch_nov24a.ino.bin sketch_nov24a.uf2

Copy uf2 file to TRINKETBOOT and tada programmed!
TODO: Look into what bin2uf2 is doing

Connecting Jlink JTAG/SWD to Trinket M0

Solder pads to SWD & SWC pins on back of Trinket M0
Connect following pins from JLink to Trinket M0:

  | black | Jlink Gnd   | Trinket M0 Gnd pin |
  | red   | Jlink VTref | Trinket M0 3v3 pin |
  | green | Jlink SWDIO | Trinket M0 SWD solder pad |
  | blue  | Jlink SWCLK | Trinket M0 SWC solder pad |

Power Trinket M0 via USB. Power Jlink via USB. "VTref" is used to detect target power is applied.

GDB to chip via Jlink JTAG/SWD - Trinket M0

Connect Jlink to Trinket M0 as above
Mostly from: https://learn.adafruit.com/debugging-the-samd21-with-gdb/
Install J-Link software from https://www.segger.com/downloads/jlink/
Run /Applications/SEGGER/JLink/JLinkGDBServer -if SWD -device ATSAMD21E18 -port 3333
Run arm-none-eabi-gdb-py

set target extended-remote :2331 (if not doing port 3333 above)

In GDB, do standard GDB things

Update bootloader via JLink JTAG/SWD w/ uf2-samd21 - Trinket M0

Connect Jlink to Trinket M0 as above
Uses OpenOCD, but expects EDBG instead of Jlink
Install openocd with brew install openocd
Modify uf2-samd21/scripts/dbgtool.js to use Jlink instead of EDBG.
- Change openocd path to use 0.1.0 or better: let openocdBin = "/usr/local/bin/openocd"
- Modify uf2-samd21/scripts/dbgtool.js: let zeroCfg = '/Users/tod/projects/samd/openocd-scripts/samd21-jlink.cfg'
Must have new openocd-script samd21-jlink.cfg:
Run "make burn" in uf2-samd21
Alternatively, run:

cd uf2-samd21
node ./scripts/dbgtool.js fuses
node ./scripts/dbgtool.js ./build/trinket/bootloader.bin

Update bootloader via JLink on commandline - Trinket M0

Connect Jlink to Trinket M0 as above
Install openocd as above
Get samd21-jlink.cfg as above

Program on commandline:

  /usr/local/bin/openocd \
   -s /usr/local/share/openocd/scripts \
   -f ~/projects/samd/openocd-scripts/samd21-jlink.cfg \
   -c "init; targets; halt; program /Users/tod/projects/samd/uf2-samd21/build/trinket/bootloader.bin verify reset; shutdown"

Can also erase entire chip:

openocd -f ~/projects/samd/openocd-scripts/samd21-jlink.cfg -c "init; targets; at91samd chip-erase; shutdown"`

Or just list which targets are connected:

  openocd -f ~/projects/samd/openocd-scripts/samd21-jlink.cfg -c "init; targets; shutdown"

TODO: Get programming to work for Arduino sketches (specifically, can program but sketch doesn't run)

TODO: try:

-c "init; targets; reset halt; program sketch.bin 0x00002000

jrincayc/samd21-programming-notes