Portenta Breakout documentation appears to show wrong JTAG pinout


I have been trying to get JTAG debugging to work with the Portenta, and I finally managed to get it to work, but it seems the documentation is incorrect.

Specifically, the PDF found on this page (the last link on the page, the full pinout diagram): Portenta Breakout — Arduino Official Store

The full pinout diagram of the JTAG connector shows the first pin is 3.3V. When I measured the pin, this appeared incorrect. It is also obvious because there are no traces running to this pin.

However the pin on the other side (pin 20, according to the documentation is supposed to be unconnected), is actually 3.3V. It appears the pinout of the JTAG connector is mirrored in the documentation.

Is the documentation wrong, or am I missing something?

Interesting observation. I‘ve tried to get the STLinkV3 to work with JTAG on the Portenta without success. Is this possible at all given that the Portenta has its special bootloader?

I have managed to get the JLink EDU and the Black Magic Probe to work with the Portenta. Debugging works fine with the Black Magic Probe for example.

AFAIK, the Portenta has a bootloader that lives at 0x8000000 - 0x8040000, and provides a way of uploading firmware using DFU via the USB-C port. The firmware starts at 0x8040000. This is the case for the M7 processor i think, i haven't done much with the M4 processor yet.

I have been able to use JLink to download the bootloader, and flash it as well. I don't think there is anything about the bootloader that prevents JTAG usage.

Next week i expect to be in possession of an STLinkV3, so i will test that as well.

EDIT: Adjusted addresses.

I can confirm that when connecting the cable like @finhst described, STLinkV3 connects to the Portenta.

I can also confirm that compiling, flashing and debugging with STLinkV3 works in combination with PlatformIO

All tested on the Core M7 - tests with M7 and M4 core are the next step I will take.

I can also confirm this. I found that the only way to connect my JLink EDU Mini was to reverse direction of the 20-pin ribbon cable connected to the Breakout's JTAG header.

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