[opentitantool] Allow changing which pins to use for JTAG

[jesultra]

HyperDebug by default does JTAG on five particular pins. However, as it is all bit-banging with no true hardware support, it is able to use almost any combination of pins.

This PR introduces a transport-specific command to "move" the JTAG functionality to a different set of pins.

Usage:
opentitantool --interface=hyperdebug transport set-jtag-pins <TCLK> <TMS> <TDI> <TDO> <TRSTn>

[BenBenderOT]

Thanks Jes. We are still testing this.

[pamaury]

Looks good to me. Is proxy support necessary?

[BenBenderOT]

The code looks good. Maybe keep the PR open until we've validated it works?

[jesultra]

Looks good to me. Is proxy support necessary?

Maybe at some point. For now, proxy support is not implemented for any JTAG functionality.

The code looks good. Maybe keep the PR open until we've validated it works?

Yes, I will wait for you Ben, to try this out on real hardware, before merging.

[jesultra]

@BenBenderOT have you had a chance to try this out on actual hardware?

[BenBenderOT]

@jesultra we tried setting to pins we needed. Still unable to confirm it worked. Hopefully today or tomorrow.

[BenBenderOT]

I'm using the "hyper310" interface instead of the "hyperdebug" interface. Should that make a difference? In any case, as soon as I try to set the pins to their default settings using the command, no signals are seen anymore and examination fails.

[jesultra]

I'm using the "hyper310" interface instead of the "hyperdebug" interface. Should that make a difference? In any case, as soon as I try to set the pins to their default settings using the command, no signals are seen anymore and examination fails.

That was unexpected. It should not matter that you use --interface=hyper310, the JTAG support is identical between that and --interface=hyperdebug.

It is hard for me to understand, how setting JTAG pins to their default setting would cause JTAG to stop working. Looking at the HyperDebug firmware code, I see a bug that can be triggered if you first do some JTAG communication, then switches JTAG pins, and then tries JTAG communication again. Could you try hitting the black reset button on your HyperDebug board, and then seeing if OpenOCD can connect? Assuming that works, then please reset again, then set the pins to their default value, and then see if OpenOCD can connect. Also, could you post the exact command you use to the pins to their default? This one should do it, but using aliases of the given pins should result in the same:

opentitantool --interface=hyperdebug transport set-jtag-pins CN7_1 CN7_7 CN7_3 CN7_5 CN7_16

[jesultra]

This feature did not work due to a silly bug in the HyperDebug firmware. With the below fix, I have observed JTAG on my CW310 work with some jumper wires to non-standard pins on HyperDebug. In plan on merging this, once the updated firmware has been included in opentitantool.
https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/5568495

[github-actions]

Successfully created backport PR for earlgrey_es_sival:

• Cherry-pick to earlgrey_es_sival: [opentitantool] Allow changing which pins to use for JTAG #23422