hifive unmatched: automatic power-on

[stefanct]

Hi,
since you have some patches for the pmic in this repo I was wondering if you have any idea how we could implement powering on the unmatched board if power of the PSU is turned on. This would greatly help people who want to turn it on remotely (e.g., due to its awful noise ;). I have been hacking a few register writes into u-boot but without lots of success yet.

I have enabled AUTO_BOOT and changed the RESET register to 0xFF but - apart from not sticking when there is a longer power loss (> ca. 5 seconds) because it is not in the OTP memory - it does not work even after short outages... Apparently there is something missing or contradicting in the configuration (or hardware)? AFAICT the nRESET pin (nRST, PORESET_N etc. nets). The PSU (and PCB) fans switch on and I can pretty much instantly see 1.8V on the reset line (thanks to setting AUTO_BOOT) - but apparently that is too early and there is no sufficient low-level pulse to make the SoC go... or maybe I am missing something and it needs something else?

There is also a thread on the sifive forum if you think this issue is not appropriate here: https://forums.sifive.com/t/automatic-power-on-when-applying-power/4768
And I'm in #riscv too...
KR