HFCLK in Pwr Mgmt Example

[Sylvain]

Hi everyone,

In the Power Management example, why the HFCLK still running when the uC is in sleep mode ? I see it in the HFCLK_STAT => State = 1

Shouldn't it be disable to optimise the consumption ?

Sincerely,
Sylvain.

[Rune Holmgren]

Hi,

How are you reading HFCLKSTAT->STATE? If you read it with the CPU the result will always be that the HFCLK is on since the CPU will automatically request the HFCLK. Generally, the HFCLK will turn itself off when it is not in use. In table 1 on in the POWER section of the product specification, it's explicitly stated that clocks will not be running after WFE/WFI sets the device into SYSTEM ON IDLE.

I haven't done any tests on hardware now, but it seems from the source code that the example isn't running the HFCLK when the system is in SYSTEM ON IDLE or SYSTEM OFF.

Best regards,
Rune Holmgren

[Sylvain]

I'm reading it on the register view of Segger when I use the debug mode ...

[Rune Holmgren]

Hi,

I talked a bit to my colleagues, and it seems like the register will always be 1 (Running) when you read it out. All ways of reading the register, including debugging, will cause the HFCLK to start. The register is most likely used internally by peripherals which check the state before starting. I am not actually sure why the register is documented at all.

Best regards,
Rune Holmgren

[Sylvain]

Ok, thank you for the answer.