Hello! I’ve been working with the Unmatched board and couldn’t help but notice the serious-looking cooling solution on the processor. Does the chip support thermal throttling if the fan is disabled and/or the heatsink is removed altogether?
I think it is poweroff not a frequency throttling which is probably not what you want, but I’m not a linux kernel expert. The sensors command will show you the board and cpu temperatures, and their min/max values.
There’s no thermal throttling implemented, just thermal shutdown. u-boot SPL configures the on-board TMP451 to trigger PMIC power-off when the FU740’s internal thermal diode exceeds 85°C (or 108°C on meta-sifive 2021.06 and earlier).
Linux doesn’t support any kind of runtime frequency scaling for FU740 today. It somewhat worked for FU540, but I don’t know what plans there are to do something for the new SoC.
Thanks, Jim and William! I was ideally hoping for runtime frequency scaling, but I’m glad it won’t fry itself at the very least. I’m hoping that feature might be implemented in the future…
CPUFreq for FU540 was never upstreamed. There current frequency for FU740 was tested in a complicated environment to be stable. Anything beyond that depends on a silicon lottery results. Folks already found the magical one line in U-Boot (a hint) which set the default clock speed, but it’s up to the user to validate that SoC produces valid and stable results over a long period of time in the right ambient temperature if changed.
Note that U-Boot upstream doesn’t have yet the patch that set temperature limit to 85C IIRC.
On per personal experience at a high temperature (~90C or so, not fully sure) the board will hang. To reach that temperature requires a high load for quite some sustained time (for me it was CPU stress tests for 40-60 minutes) and SoC fan disabled.
Thanks for the info, David! Regarding the magical one line in U-Boot, do you have any additional information/insight into which line would need to be changed, and how difficult it might be to change that line? I’d be interested in under-clocking the SoC if at all possible to reduce the CPU temps.