[time-nuts] iPhone keeping better time?

Hal Murray hmurray at megapathdsl.net
Wed Nov 16 15:56:23 EST 2011

> Chris, I can see your point, but these devices must have a CPU running all
> the time, otherwise how would the soft power-up work?  Can the drain of a
> CMOS clock chip such as that used in millions of PCs be all that much  more?

CPU chips used in battery powered systems typically have a way to turn off 
the CPU until an interrupt arrives.  If you are serious, you turn off the CPU 
clock too.  That means you can only get woken up by the CMOS clock or an I/O 
device that has it's own clock.  Yes, it takes time (few ms) to turn the 
clock back on.

The numbers are impressive.  If you use SRAM rather than DRAM, you don't need 
memory refresh.  Many modern ARM chips include flash and SRAM.  They aren't 
big enough for a phone full of bloatware, but the idle current is hard to 

These are my opinions, not necessarily my employer's.  I hate spam.

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