Messages in this thread | | | From | Bodo Eggert <> | Subject | Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override. | Date | Mon, 07 Jan 2008 20:38:09 +0100 |
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Christer Weinigel <christer@weinigel.se> wrote:
> How do you find out the speed of the ISA bus? AFAIK there is no > standardized way to do that. On the Geode SC2200 the ISA bus speed is > usually the PCI clock divided by 4 giving 33MHz/4=8.3MHz or > 30/4=7.5MHz, but with no external ISA devices it's possible to > overclock the ISA bus to /3 to run it at 11MHz or so. But without > poking at some CPU and southbridge specific registers to find out the > PCI bus speed and the ISA bus divisor you can't really tell.
If you overclock, you are on your own. IIRC I've used 13,3 MHz for some time and used a lower PIO mode to compensate.
> So if you do udelay based on a 6MHz clock (I think you can safely > assume that any 386 based system runs the ISA bus at least that fast) > you'll waste at least 30% and maybe even 100% more time for the delay > after every _p call.
Defaulting to 8 MHz and offering an option to set another clock speed (like idebus=) should be OK.
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