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Re: PCI Clock speed.
- To: Mailing List Recipients <firstname.lastname@example.org>
- Subject: Re: PCI Clock speed.
- From: "John R Pierce" <email@example.com>
- Date: Wed, 18 Feb 1998 18:45:01 -0800
- Resent-Date: Wed, 18 Feb 1998 18:51:10 -0800
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- Resent-Message-ID: <"DvKfo3.0.MK3.8nvwq"@electra.znyx.com>
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>Is there a way to determine the PCI clock speed for a given system. I
>have a board that has a timer which is incremented once per PCI clock.
>To determine the PCI clock speed, I calculated the number of ticks in
>this timer over a period of 5 seconds which was clocked by the PC timer
>and then did a divide to determine the frequency. If I didn't have this
>timer, I would not have been able to determine this frequency.
>In addition, if I didn't have this timer, I probably wouldn't need to
>know the PCI clock rate. But that's a different subject. It seems
>that there should be a system call in the PCI bios that shall give this
'Fraid not. To start with, its not necessarily a constant. Various power
down states can slow the bus clocks down, the spec allows DC to 33MHz. Some
advanced systems have been rumored to use a dithered clock to minimized RF
emissions, this is well within bus specs. The only requirement is the
minimum high and low time.