From owner-freebsd-arch Thu Jan 3 17:33:55 2002 Delivered-To: freebsd-arch@freebsd.org Received: from mailman.zeta.org.au (mailman.zeta.org.au [203.26.10.16]) by hub.freebsd.org (Postfix) with ESMTP id B409C37B417 for ; Thu, 3 Jan 2002 17:33:52 -0800 (PST) Received: from bde.zeta.org.au (bde.zeta.org.au [203.2.228.102]) by mailman.zeta.org.au (8.9.3/8.8.7) with ESMTP id MAA20115; Fri, 4 Jan 2002 12:33:42 +1100 Date: Fri, 4 Jan 2002 12:34:08 +1100 (EST) From: Bruce Evans X-X-Sender: To: Poul-Henning Kamp Cc: Mike Silbersack , Subject: Re: DELAY accuracy Re: cvs commit: src/sys/dev/usb uhci.c In-Reply-To: <4584.1010098579@critter.freebsd.dk> Message-ID: <20020104122618.P18879-100000@gamplex.bde.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-arch@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG 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