Allow lower cpu frequencies for esp32

[ss89]

Describe your request

I would like to be allowed to set lower cpu frequencies than 80Mhz for my esp32-c6.
Theoretically it should be able to go as low as 10MHz (Arduino IDE suggests this as lowest clock value).

Why the uncertainty?

It's an existing feature, but only the allowed values for certain MCUs might need adjustments

Use cases

This should allow the battery powered device to last as long as possible.

What areas might this affect?

anything related wifi, as esp32-c6 can't use wifi below 80Mhz clock speeds (as Arduino IDE suggests)

Anything else?

No response

[clydebarrow]

What makes you think it can go lower? According to the datasheet the only choices with a 40MHz crystal are 160, 80 and 40. To go lower you need to change the crystal.

[ssieb]

I checked the technical references. The original ESP32 can do just about any frequency it seems.
And from the ESP32C6 technical reference:

CPU_CLK is the master clock for CPU and it can be as high as 160 MHz when CPU works
in high performance mode. Alternatively, CPU can run at lower frequencies, such as at 2 MHz, to achieve
lower power consumption.

But if you aren't using the normal high speed clock, you can't do wifi or BT and depending on which clock you're using and how you've set it, various peripherals can be affected as well.

[clydebarrow]

Well, good luck with that, just because it can run at 2MHz doesn't make it easy to achieve. As I already said you would have to change the crystal - that would require finding a 2MHz one to fit in place of the 40MHz, might be hard to start with, then some decent SMD rework equipment and skills. Or you could design your own board. And then what would you do with it? No Wifi, no Bluetooth etc.

So it's not something ESPHome (or any software solution) can help with. If you want low power, maybe look at the nRF52 series (which is supported by ESPHome, no WiFi but has Bluetooth) which is much lower power than the ESP32.

[ssieb]

You don't need to change the crystal. There's an alternate internal clock source you can use.
This is a valid request, but no guarantees about anyone implementing it.

[clydebarrow]

I checked the technical reference manual, and while there are a couple of choices for clock sources, none of them result in a CPU frequency lower than the crystal frequency. If you have other information, please share it.

[clydebarrow]

Looking again, there is an RC_FAST_CLK that can be selected, that would give lower frequencies - I didn't see that the first time. So fair enough, it can probably be done.