From owner-freebsd-questions Thu Apr 25 16:34:27 1996 Return-Path: owner-questions Received: (from root@localhost) by freefall.freebsd.org (8.7.3/8.7.3) id QAA20087 for questions-outgoing; Thu, 25 Apr 1996 16:34:27 -0700 (PDT) Received: from phaeton.artisoft.com (phaeton.Artisoft.COM [198.17.250.211]) by freefall.freebsd.org (8.7.3/8.7.3) with SMTP id QAA20052 for ; Thu, 25 Apr 1996 16:34:05 -0700 (PDT) Received: (from terry@localhost) by phaeton.artisoft.com (8.6.11/8.6.9) id QAA25840; Thu, 25 Apr 1996 16:23:59 -0700 From: Terry Lambert Message-Id: <199604252323.QAA25840@phaeton.artisoft.com> Subject: Re: Programmed I/O To: metabyte@netcom.com (Sangeeta Relan) Date: Thu, 25 Apr 1996 16:23:58 -0700 (MST) Cc: questions@FreeBSD.ORG In-Reply-To: <317FF410.1FEF@netcom.com> from "Sangeeta Relan" at Apr 25, 96 02:52:16 pm X-Mailer: ELM [version 2.4 PL24] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-questions@FreeBSD.ORG X-Loop: FreeBSD.org Precedence: bulk > Can I get info on how the Programmed I/O is performed on FreeBSD systems? By causing your expensive, fast, processor to buzz-loop on port addresses for your cheap, slow, devices waiting for "data-ready" bits to become active, just like "Programmed I/O" in any other OS. Tying up your expensive, fast, processor, when it could be better utilized doing tings like adding numbers or otherwise executing code in the L1 cache (which on a P5/166 system is 5 times more efficient than accessing crappy device registers on a 33MHz EISA or PCI bus -- assuming you aren't doing PIO to an ISA device, in which case it's 8MHz and L1 is ~21 times as efficient as doing PIO). Good reason to use bus-mastering devices, don't you think? A fast machine doing PIO is the moral equivalent of hiring Dirty Harry as a cop, then assigning him duty as a crossing guard... Harry would be over-powered and under-utilized ("C'mon punk, cross my street!"). Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers.