The MCULink-Mini Is a Shrunken, Cost-Reduced But Fully-Featured Open-Hardware Debug Probe
Based on NXP's original MCU-Link, this debug probe can be used externally, installed as a module, or integrated into KiCad projects.
Embedded engineer and professor Erich Styger has shown off an open-hardware debugging tool, developed at the Lucern University of Applied Sciences and Arts, which can act as an external probe, an internal debug module, or be integrated into custom board designs.
"Who needs a debug probe, if you have printf()? If doing serious development, you most likely want a hardware debug probe," Styger writes. "We at the HSLU IET use different hardware, boards and kits, and for many of the classroom equipment it is very useful to have the debug probe embedded on the target board: less cables, easier to use.
"For this we have developed a new Open Source Hardware (OSHW) debug probe in KiCad which can used in different ways: as external debug probe, integrated and soldered on top of the target board, or fully integrated and embedded into a custom design."
Designed by Dario Scheuber under Styger's tutelage, the MCULink-Mini is based on the NXP MCU-Link CMSIS-DAP Debug Probe — but, as the name suggests, is considerably smaller. Despite its shrunken dimensions, the MCULink-Mini offers full firmware compatibility with the full-size MCU-Link — including support for the NXP LinkServer, SMSIS-DAP, and Arm's DAPLink. The original board's micro-USB connector has been swapped out for the more modern USB Type-C, which can also serve to debug the board's own NXP LPC55S69 chip.
Other improvements on NXP's original include a more compact connector for the board's UART serial bus, the ability to switch between firmware update and regular boot with a button rather than jumpers, and the ability to be used in three ways: as a standalone external debugging tool, like the original MCU-Link; soldered directly onto a target board as an internal debug module, using its castellated pins; or as an embedded design that can be integrated into other KiCad projects directly.
Designed to use a two-layer PCB in order to keep costs down, the MCULink-Mini is keenly priced: Styger estimates that it would cost around $12 per unit to have 100 units assembled at a PCB production facility, including all components.
For those who want to give it a go, the board's design files have been released under the permissive MIT license on Styger's GitHub repository — though it comes with the warning that, lacking level shifters, it can only be used with 3.3V target devices.
More information on the MCULink-Mini is available on Styger's blog.