--- (---.delete@this.redheron.com) on September 13, 2021 11:19 am wrote:
> - one thing Apple do (I don't know about other designs) is slide voltage up and down while keeping frequency
> unchanged. Obviously changing frequency is somewhat disruptive in a way that changing voltage is not.
> Apple have some flexibility to do this given the digital power estimators, a knowledge of the capacitance in
> the system, and an ability to prevent catastrophe if the system is oversubscribed by having instruction issue
> paused by the DPE for a cycle or two. Maybe also the fact that every SRAM is decoupled from logic with a voltage
> shifter between the two, so you have flexibility to down-voltage logic while not losing SRAM retention.
> (At least they have a long sequence of patents about this, so you'd hope it's implemented!)


I'm a little confused on this point. Why would you want to alter voltage while keeping frequency constant? Shouldn't you always want to run at the lowest voltage capable of handling a given frequency to minimize power? In what circumstance would you for example want to increase voltage while keeping frequency constant? That makes no sense to me, but maybe I'm missing something.