Date: Fri, 4 Jan 2002 12:34:08 +1100 (EST) From: Bruce Evans <bde@zeta.org.au> To: Poul-Henning Kamp <phk@critter.freebsd.dk> Cc: Mike Silbersack <silby@silby.com>, <freebsd-arch@FreeBSD.ORG> Subject: Re: DELAY accuracy Re: cvs commit: src/sys/dev/usb uhci.c Message-ID: <20020104122618.P18879-100000@gamplex.bde.org> In-Reply-To: <4584.1010098579@critter.freebsd.dk>
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On Thu, 3 Jan 2002, Poul-Henning Kamp wrote: > In message <20020104094446.N18171-100000@gamplex.bde.org>, Bruce Evans writes: > >On Thu, 3 Jan 2002, Poul-Henning Kamp wrote: > >> Either way, in i386 I think DELAY(1) would be best implemented as > >> inb(0x80) > > > >This mistake has been made before. inb(0x80) is too fast on some machines. > > Are you sure ? I have yet to see a machine where 0x80 isn't routed > to hardware since it is the "magic" bios-post address... I haven't seen one either, but this behaviour was reported for old machines. Perhaps it was actually for 0x84, which was used for "FASTER_NOP" in FreeBSD-1. Support for historical kludges is more standard now, so I wouldn't expect new machines to optimize this. OTOH, the timing for accesses to ordinary "ISA" ports is very machine dependent. Bruce To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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