Setting ARM/core/RAM frequency has no effect

[okenido]

Hello,

I'm using the mailbox interface of the RPI (https://github.com/raspberrypi/firmware ... -interface) in a bare metal app to change frequency settings of arm/core/ram but none of them seems to make the processing faster or slower.

Asking the mailbox for the current frequency returns the right values after I set them.

I wanted to do that since the default frequency reported by a mailbox call is 600Mhz for the ARM core and something like 250Mhz for the SDRAM... I read about topics saying that the CPU is in low-power state by default for bare metal apps. But no matter if I set 1.4Ghz or 100Mhz it seems to have no effect at all. (RPI 3B+)

Am i doing something wrong ?

[LdB]

The call works and as you are getting the current value (at least part of your code works) so all I can say is check your values/code

Tag id: 0x00038002
data size provided : 8
data_size response: 8,
clock id: 0x3
speed to set (1.2Ghz): 1200000

If you still have problems provided code, it would be a lot easier

[okenido]

Okay so it took a while to figure it out, I had literally forgot about this problem.

I found it wasn't working because my RPI was undervolted ! (power supply lower than 4.8V). I knew it was undervolted so I hid the little bolt icon, but I haven't tought that it could prevent the CPU from running higher than its default low-speed, which in reality make sense.