Hi,
I like to save some power and downclock a RavPower WD03.
How can this be done? Do I need to modify the u-boot partition?
Thanks,
mwarning
If your device exposes /sys/devices/system/cpu/cpufreq/ you can often fix the clock speed there.
Generally, you'll find
$ cat /sys/devices/system/cpu/cpufreq/policy0/scaling_governor
ondemand
which automatically reduces the clock speed when not under load.
I'd suggest to actually measure the results though, as it's very unlikely that you'll see a significant difference in your power consumption just by changing the CPU frequency.
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These paths do not exist. I also used find to try to locate these options. But without success.
Afaik it's fixed and set by Uboot (check the bootlog in the device page). If you have serial console you can interrupt boot by pressing "i" when it tells you and then you can look at uboot environment (configuration) with printenv
If you are lucky it's a variable you can change with setenv variablename='value' and then saveenv.
If you can't do that, then you need to alter uboot source, then compile and flash a new uboot.
Afaik CPU clock speed isn't particularly important on that SoC. Biggest power drain is the wifi chip, so try to reduce wifi transmit power and add other options that make it more power-efficient.
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@bobafetthotmail thanks, that is a good idea and I will give it a test tomorrow. But I already checked the u-boot settings partition and couldn't find something related to clock speeds.
(btw. this change isn't only about power consumption, but EV conformity as well.)
Isn't the hardware compliant already?
compliant to what?
Ask him/her/it. Not me.
It depends on the country and use case. E.g. use in medical scenarios would have a much more stricter EV limit. Clocking down the cpu/memory can be necessary in these cases.
I'm assuming you mean electromagnetic interference here. I don't understand why are you trying to do that in the first place as devices not certified will remain not certified, even if compliant.
And for serious use what matters is the certification, they don't have an EM detector to scan your stuff and decide for each device.
That said, did you try wrapping tinfoil around the board and connecting it to ground (negative electrical contact) to create an EM shield? (use a layer of non-conductive material like plastic or paper between the shield and the board to not cause massive shorts)
Only thing you should leave uncovered is the antenna for obvious reasons.
@bobafetthotmail I like the devices in questions to adhere to stricter standards. Also, the antennas are internal and the case is glued. I just want to try to downclock components and see if it helps.
EM interference is overrated.
That said, I'm talking about shielding because I know power regulator components (buck or boost converter) can be very big EMI sources if none has mitigated this by designing the circuit accordingly, and I quite frankly believe that EMI mitigation is a very secondary topic for designers of such cheap devices.
Then OP shouldn't buy cheap devices if it's interested in the EMI...
I think this is getting a bit off-topic.
You already had your answer: the device cannot be downclocked.
and that the most likely cause of EMI in this class of device isn't CPU/RAM but cheaply designed power distribution circuits.