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Programming & Debugging

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Flo edited this page Sep 26, 2025 · 3 revisions

⚡ Flashing the bootloader

A factory new SAMD21 IC ships without any firmware. For programming, it requires a compatible SWD programmer. The adafruit bootloader is used.
A binary of a custom breezedude version is included in this repo (only changed the USB PIDs & descriptor and names of the bootloader flash drive)

Compatible programmers:

  • Segger J-Link (EDU)
  • DAPLink / CMSIS-DAP

⚠️ST-Link does not work with SAMD21

For flashing:

  • Connect SDWIO, SWDCLK, GND and apply battery voltage for flashing.
  • Flash the binary with the tool of your chice
  • The blue LED should start fading after flashing.
  • After flashing the bootloader once, the firmware and bootloader can be updated by drag&drop UF2 updates.

1.27mm Pinheader as kind of a pressfit the SWD socket. Make sure to connect GND to your computer if powering externally.

🔗 Using DAPLink / CMSIS-DAP

For just flashing the bootloader binary a cheap open-ocd compatible DAPLink / CMSIS-DAP programmer is the easiest choice.
Install open-ocd according to its documentation (+add to PATH)

Bootloader flashing using as programmer

Connect the PCB and run

openocd -f interface/cmsis-dap.cfg -f target/at91samdXX.cfg -c "program bootloader-breezedude-v3.16.0-19-atmel.bin verify reset exit 0x00000000"

within the bootloader directory.

output should look like this:

openocd -f interface/cmsis-dap.cfg -f target/at91samdXX.cfg -c "program bootloader-breezedude-v3.16.0-19-atmel.bin verify reset exit 0x00000000"
Open On-Chip Debugger 0.12.0 (2025-07-10) [https://github.com/sysprogs/openocd]
Licensed under GNU GPL v2
libusb1 d52e355daa09f17ce64819122cb067b8a2ee0d4b
For bug reports, read
        http://openocd.org/doc/doxygen/bugs.html
Warn : DEPRECATED: auto-selecting transport "swd". Use 'transport select swd' to suppress this message.
Info : Using CMSIS-DAPv2 interface with VID:PID=0x0d28:0x0204, serial=00000080003400454e00000e4e574c50a5a5a5a597969908
Info : CMSIS-DAP: SWD supported
Info : CMSIS-DAP: SWO-UART supported
Info : CMSIS-DAP: Atomic commands supported
Info : CMSIS-DAP: Test domain timer supported
Info : CMSIS-DAP: FW Version = 2.1.0
Info : CMSIS-DAP: Serial# = 00000080003400454e00000e4e574c50a5a5a5a597969908
Info : CMSIS-DAP: Interface Initialised (SWD)
Info : SWCLK/TCK = 1 SWDIO/TMS = 1 TDI = 0 TDO = 0 nTRST = 0 nRESET = 1
Info : CMSIS-DAP: Interface ready
Info : clock speed 400 kHz
Info : SWD DPIDR 0x0bc11477
Info : [at91samd.cpu] Cortex-M0+ r0p1 processor detected
Info : [at91samd.cpu] target has 4 breakpoints, 2 watchpoints
Info : [at91samd.cpu] Examination succeed
Info : [at91samd.cpu] starting gdb server on 3333
Info : Listening on port 3333 for gdb connections
[at91samd.cpu] halted due to debug-request, current mode: Thread
xPSR: 0x21000000 pc: 0x00000268 msp: 0x20002de0
** Programming Started **
Info : SAMD MCU: SAMD21G18A (256KB Flash, 32KB RAM)
** Programming Finished **
** Verify Started **
** Verified OK **
** Resetting Target **
shutdown command invoked

🐞 Debugging the Code

🐛 SWD

For Debugging CMSIS-DAP is currently not supported out of the box for SAMD21. ToDo: Custom script for using open-ocd

The following should work (see PIO docs)

🖥 USB

There is a basic-debug of the Breezedude using the USB connection and the WebSerial terminal of the configurator. With this you can check for basic functionality and forward the WS80/WS85 UART debug messages to check the sensor output.

⚠️ As the USB connection changes the software behavior, in this mode it does not transmit FANET data.



💻 UART

For full-debugging (normal operation with deepsleep) connect a TTL (3.3V) UART to Serial adapter to the TX1 pad on the bottom of the PCB. Remember to have GND connected as reference.

⚠️ Software before 2025-09 need to be debugged on the TX pin of UART sensor port (black connector).
You can use an adapter cable or solder directly to the back of the PCB.

Use a serial Terminal of your choice, like putty or hterm to view the data. This debug mode works while normal operation if DEBUG=1 is enabled in the settings file. Make sure to disconnect USB for normal operation.

📺 I²C Display

For on-site testing a SSD1306 OLED display can be connected to the I2C connector (blue).

❗ The display needs to be connected on boot/reset and DEBUG=1 enabled.



⚠️ This feature is not optimized or frequently tested

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