On how to use HVPULSE manually while still connected to the RP

[doegox]

Hello

From the schematics and the code it seems HVPULSE is constantly driven by the RP gpio so it seems a bit dangerous to overwrite the signal with an external trigger source without disconnecting first the RP.
Would it make sense to modify the RP firmware such that:

• picoemp_configure_pulse_output configure it with a pull-down, idle state is HiZ + pull-down
• picoemp_pulse set to high then back to HiZ

So we could overwrite HVPULSE with an external source without worry.

[colinoflynn]

There's no theoretical issue with doing that - I think the external usage was discourage as a "regular user" because there is a risk of blowing up T1 or R3 (this isn't validated though). Basically if you turn on Q4 I'm not sure if you'll burn up T1/R3, since it's not designed for continuous drive. External triggering made sense to go via the RPi so that it served as a safety against turning on Q4 for more than a few mS.

So I think I'd prefer not to have such options enabled by default, but if someone e.g. uncomments/redefines something that means they enable that feature I think it makes sense. Just want users to be aware there is a high risk that they'll damange hardware when doing that (if e.g., they accidently plug the HVPULSE line into a constant 3.3V source, or if they are debugging code that drives that line high).

[LennertW]

You should be able to use the external_hvp command to configure the HVPULSE pin as an input (but currently without a pull-down). This does mean that you have to activate the mode, which is probably less convenient compared to what @doegox describes.

This can probably be improved, but it worked well during my (limited) testing. I used that external hvp mode for this example: https://github.com/KULeuven-COSIC/SimpleLink-FI/blob/main/notebooks/5_ChipSHOUTER-PicoEMP.ipynb

[doegox]

Thank you for sharing your notes @LennertW !