[ntp:questions] Re: linux system clock egregiously slow!

Hal Murray hmurray at suespammers.org
Thu Jan 22 03:44:15 UTC 2004


>Timer #5 is running off a 27MHz crystal with a spec of +/-30PPM.
>Since the MIPS core is running at 300MHz, I expect that the error in
>setting timer #5 is on the order of ten times smaller than the crystal
>error.

Some systems FM modulate the main clock to reduce EMI troubles.
(aka spread spectrum)

I think 800 ppm could be in the right ballpark.  The main clock would
be slow in order to avoid overclocking the CPU.  Is that sign right?
(On my PC, it's big enough to be easy to measure.)


>Hal> Print out the value and see if it makes sense.

>It says about 149MHz, which is what I expect.

Does the MIPS cycle counter count every other cycle?  If so, I'd
expect 150 rather than 149.

How close is your "which is what I expect"?  Is it 
within a few PPM, or is it off enough to explain what
you are seeing?

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