RE: Real PCI Clock Rates

["Ingraham, Andrew" <Andrew.Ingraham@compaq.com>]

>I'm wondering whether I should
>expect to see less than 33MHz in actual practice.

The crude answer is, yes, you should "expect" to see less than 33MHz (down
to 0Hz), or less than 66MHz (33-66MHz).  If you decided not to expect slower
clock rates and designed something that doesn't accommodate them, it would
not comply with PCI requirements.

Will you actually see such reduced clock rates?  Yes.  My poor older
Pentium-class PC at home runs the PCI bus at something like 25MHz or 30MHz
(with the CPU that's installed in it) because it's synchronous with the CPU
clock and there isn't a convenient ratio at 33MHz.  Laptops *might* throttle
the clock down in quiet mode, but I don't know for sure if any actually do.
Because 66MHz timing is very tight, it would not surprise me if they find it
necessary to run somewhat slower.

Regards,
Andy