Running STM32H745 at 480 MHz and using WFI

[Terry Greeniaus]

Hello,

In RM0399 Rev 3, way down in the SYSCFG section 13.3.10 describing SYSCFG_PWRCR, we have the following note at the end of the register description:

"Note: VOS0 must be activated only in VOS1 mode. It must be disabled by software before entering low-power mode (execution of WFE/WFI instruction)."

To operate at 480 MHz, we have to use VOS0 mode. But does this really mean we can't use WFI unless we first drop to 400 MHz? And after we wake up we need to set the clock back up to 480 MHz? That seems a bit insane to me and I'm surprised that this limitation isn't mentioned anywhere else in the manual or in the chip datasheet.

Is this a real limitation of the device or is that random note an error? Maybe it's referring to a lower-power mode other than just CSleep?

Thanks,

TG

[Bouraoui Chemli]

Hello @Terry Greeniaus​ 

It is spec device but it doesn't impact sleep mode.

Bouraoui

[Piranha]

This is not an acceptable answer! Please rephrase it in a clear and unambiguous way.

[Bouraoui Chemli]

This is the device spec, we need to switch from VOS0 to VOS1 when entering low-power modes (Stop/Standby). This doesn't have an impact on sleep mode.