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Getting Low Power With USB When Not Suspended (STM32F415RG)

chuck2399
Associate II
Posted on March 31, 2016 at 21:57

Hi,

We're trying to reduce power consumption when not suspended and using USB.  During the time when we are not handing USB interrupts, we would like to run at a slower core clock speed.  I'm wondering if this is possible or not?

Looking at CubeMx and the Reference Manual, I see that the AHB clock must be 30MHz or higher for the USB HS PHY.  However, I also see that this clock is used to access the USB registers.  So, my question is if I can switch the SYSCLK to use the HSI using the System Clock Mux as long as I am not accessing the USB peripheral?  This would bring the AHB down to 16MHz.  I would then disable interrupts and do a WFI and then use the PLL clock again after I wake.

If I can do this, are there steps I need to take when I switch back to the PLLCLK?  For example, do I need to set the HRST bit in the USB PHY?  

If I can't do this, is there a suggestion?  We don't really want to run at full tilt when we aren't doing anything.

Thanks.

#clocks #usb #power #system
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