OpenOCD-ready HAT turns the Pi into a debugger with Cortex-M and JTAG headers

OpenOCD-ready HAT turns the Pi into a debugger with Cortex-M and JTAG headers

May 26, 2021 — by Eric Brown

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Blinkinlabs’ $27, open-spec “JTAG HAT” that turns the Raspberry Pi into an OpenOCD compatible MCU debugging device with built-in Arm Cortex-M and JTAG headers.

Netherlands-based Blinkinlabs has launched a JTAG debugging HAT for the Raspberry Pi for 22 Euros ($27) that supports the open source OpenOCD debugging software. The JTAG HAT is equipped with a 10-pin, 1.27mm Cortex-M Debug Connector that supports level-shifted JTAG (TCK/TMS/TDI/TDO) or SWD (SWDIO/SWDCLK) debugging pins. There is also a standard 20-pin JTAG header with 0.1-inch headers for “easy connection to boards with older or no pins.”

JTAG HAT with Pi (left) and Cortex-M Debug cable connection to target
(click images to enlarge)

Blinkinlabs created the JTAG HAT to make it easier to use the Raspberry Pi for debugging, which offers the advantage of a network connection and greater flexibility than debuggers designed for certain types of microcontrollers. The HAT avoids the need to fit the Pi with specific conversion cables for each MCU to connect the Pi’s 0.1-inch headers with 1.27mm pins.

The company did not go so far as to call it a universal debugger, but that is the general idea. Between the 10-pin Cortex-M connector, the OpenOCD support, and the legacy JTAG header, the HAT should support debugging of a wide variety of devices including STM32 and ESP32, says Blinkinlabs. The HAT can use any HAT-ready Raspberry Pi and is said to be a good match for an older Pi that has been sitting on a shelf.

The JTAG HAT, which we saw on CNXSoft, provides level converters/buffer drivers to program devices at voltages such as 1.8V or 5V. There is also a hardware reset, a level-shifted UART for communicating with the target, and a current sensor for measuring the power drawn by the target.

Further information

The JTAG HAT is available for 22 Euros ($27). More information may be found on Blinkinlabs’ product/shopping page and GitHub page, where you will find schematics, Altium source files, documentation, and setup instructions.