Date: Sat, 18 Nov 1995 14:40:55 -0700 (MST) From: Terry Lambert <terry@lambert.org> 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: <199511182140.OAA09716@phaeton.artisoft.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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> >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. Otherwise I would > have used it in DELAY(). The only way it can be reliable is if all buses > know it is special and put something there that inserts wait states to > extend the i/o time to 1.25us. Time to scream about high resoloution kernel timers once again? A nice reschedulable one-shot HRT interface would fix DELAY right up. There are only *minor* kernel preemption issues involved. Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers.
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