Date: Sat, 18 Nov 1995 16:54:48 +0100 (MET) From: hm@altona.hamburg.com (Hellmuth Michaelis) To: bde@zeta.org.au (Bruce Evans) Cc: bde@zeta.org.au, hm@altona.hamburg.com, freebsd-hackers@freebsd.org, hosokawa@mt.cs.keio.ac.jp Subject: Re: DELAY's in syscons Message-ID: <m0tGpbM-00001PC@ernie.altona.hamburg.com> In-Reply-To: <199511181324.AAA25738@godzilla.zeta.org.au> from "Bruce Evans" at Nov 19, 95 00:24:23 am
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>From the keyboard of Bruce Evans:
> >> DELAY(n) only delays n-20 usec on an infinitely fast machine so it
>
> >If not told otherwise, pcvt does NOT use DELAY() for exactly the reason
> >you just describe.
>
> >Instead it uses dummy reads from port 0x84 which execute in a defined time
> >of ~= 1,25us. (IF they ever do execute - i was told that some implementations
> >do know that there is nothing to read from port 0x84 and somehow don't let
> >this read though to the bus, the result is, that these reads do execute very
> >fast).
>
> I think this only works reliably for 8MHz ISA buses.
Exactly - it works on ISA and EISA machines but not necessarily on PCI.
hellmuth
--
Hellmuth Michaelis hm@altona.hamburg.com Hamburg, Europe
(A)bort, (R)etry, (I)nstall BSD ?
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