Does anyone knows how to use the Raspberry Debug Probe with a Raspberry Pi 3B? I've googled but the articles I've found only explains how to use it with Raspberry Picos. I have a tricky issue to diagnose and it needs hardware level debugging to see what's going wrong with it.
Many thanks if you can point me in the right direction.
What do you want to debug? The regular Pis have JTAG to which you can hook up a debug probe and run something like OpenOCD+gdb on another machine (you can likely do that from another Pi using GPIO, or a USB JTAG widget). But you're debugging the whole OS including all the daemons and whatnot that are running on it. Unless your issue is with the kernel itself (eg a boot failure) or with some code running bare-metal, I don't think JTAG is going to help much.
The Pico's Debug Probe provides SWD, which is for microcontrollers but not for application-cores on the big Pis. It provides 2 signal wires where JTAG needs 4, so I don't think you could repurpose it for JTAG even if you wanted to.
Theo
So that's the difference, thanks for the info, much appreciated. To sum up SWD on the Raspberry Pi probe only good enough for rp2040s and others with SWD.
What do you suggest I use on raspberrypi instead? It is indeed the boot process I need to debug. It is working OK in Qemu 9.x but does not boot on real rpi hardware, either rpi3 and rpi4.
I'd maybe try a second RPi running OpenOCD and the GPIO to drive the JTAG pins on the first RPi:
Thanks, that's useful information, I appreciate that.
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