Erich Styger's picoLink Is a Low-Cost Alternative to the Raspberry Pi Debug Probe
Compatible with anything that can talk CMSIS-DAP, this Arm-focused debugger includes two different headers and USB Type-C connectivity.
Embedded engineer Erich Styger has designed an open source debug probe powered by the Raspberry Pi RP2040, but compatible with anything that responds to Arm's CMSIS-DAP standard: the picoLink.
"The good thing with the Raspberry Pi Pico/RP2040 ecosystem is: one can use another RP2040 Pico board as a debug probe to debug other Arm Cortex-M devices," Styger explains. "But instead using a Raspberry Pi Pico board with some wires, why not building a dedicated board? The result is a small, versatile and open source debugging probe which virtually can debug any Arm Cortex-M device as a standard Arm CMSIS-DAP probe."
The project was inspired, in part at least, by the official Raspberry Pi Debug Probe, which itself builds on an open source firmware for the Raspberry Pi Pico's RP2040 microcontroller — but addresses some shortcomings Styger identified with the design. "It uses different pins according to the schematics information, so the current PicoProbe firmware won’t be compatible," he explains. "Instead of the standard Arm 2×10 pin SWD/JTAG connector, it uses the ‘Raspberry Pi’ ‘non-standard’ 3-pin cable connector. [And] It uses micro-USB instead of USB-C."
The picoLink, by contrast, is a smaller board roughly the size of the Raspberry Pi Pico itself, uses the same pins as expected in the stock PicoProbe firmware, features a standard Serial Wire Debug (SWD) ten-pin header alongside a three-pin header for the Raspberry Pi range, and includes USB Type-C for power and debug connectivity. "Rather minor," Styger admits of the latter point, "but USB-C cables are getting more and more common."
Styger's design has another advantage over the official Raspberry Pi probe, too: price. "The BOM costs are around the normal [Raspberry Pi] Pico board," Styger explains, "about half of the price for the Raspberry Pi Debug probe: ~$5.00 single quantity, add ~$2 for cables."
Styger has indicated that the picoLink will be released as open source hardware, though at the time of writing neither design files nor source code had been published to his GitHub repository. More information is available on Styger's website.