Date: Sat, 18 Nov 1995 13:38:27 +0100 (MET) From: hm@altona.hamburg.com (Hellmuth Michaelis) To: bde@zeta.org.au (Bruce Evans) Cc: freebsd-hackers@freebsd.org, hosokawa@mt.cs.keio.ac.jp Subject: Re: DELAY's in syscons Message-ID: <m0tGmXL-00001XC@ernie.altona.hamburg.com> In-Reply-To: <199511181058.VAA20290@godzilla.zeta.org.au> from "Bruce Evans" at Nov 18, 95 09:58:46 pm
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>From the keyboard of Bruce Evans:
> DELAY(n) only delays n-20 usec on an infinitely fast machine so it
> shouldn't be called with n <= 20 unless the precise delay doesn't matter.
> Syscons and pcvt call it with delays <= 10 usec when the precise delay
> does matter.
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).
hellmuth
--
Hellmuth Michaelis hm@altona.hamburg.com Hamburg, Europe
(A)bort, (R)etry, (I)nstall BSD ?
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