Tim Waugh wrote:
> On Sun, Jul 02, 2000 at 03:42:37PM +0200, Gunther Mayer wrote:
>
> > this patch shows some register access times if TSC is available.
>
> Nice.
>
> > My Mainboard P3B-F seems to have 4.33MHz ISA speed (750ns *8/4.33 ~ 1350),
> > anybody knows why this isn't 8 MHz ?
>
> Wait states (is that the right name)? The CPU has to wait for the ISA
> bus first.
Yes, but this is already accounted for:
An ISA I/O read cycle takes 6 ISA bus cycles (according Axelsons "Parallel Port complete")
- 6 cycles at 4.33 Mhz take 1385ns (230ns cycle time)
- 6 cycles at 8 MHz take 750ns (125ns cycle time)
I timed access to an unused port and this took the same time.
So I rather assume my ISA bus is running at about 4 MHz.
The BIOS provides further wait states for older cards, I have
selected the fastest value (I/O recovery time).
But this contradicts PIIX4 PCI-ISA bridge documentation, where
the ISA speed is documented as 7.5-8.33 MHz (1/4 PCI speed).
Hints?
Regards, Gunther
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