From owner-freebsd-hackers Wed Nov 19 18:25:49 1997 Return-Path: Received: (from root@localhost) by hub.freebsd.org (8.8.7/8.8.7) id SAA26709 for hackers-outgoing; Wed, 19 Nov 1997 18:25:49 -0800 (PST) (envelope-from owner-freebsd-hackers) Received: from out1.ibm.net (out1.ibm.net [165.87.194.252]) by hub.freebsd.org (8.8.7/8.8.7) with ESMTP id SAA26700 for ; Wed, 19 Nov 1997 18:25:43 -0800 (PST) (envelope-from mouth@ibm.net) Received: from slip129-37-53-101.ca.us.ibm.net (slip129-37-53-101.ca.us.ibm.net [129.37.53.101]) by out1.ibm.net (8.8.5/8.6.9) with SMTP id CAA246922; Thu, 20 Nov 1997 02:25:32 GMT From: mouth@ibm.net (John Kelly) To: Bruce Evans Cc: hackers@freebsd.org Subject: Re: Status of 650 UART support Date: Thu, 20 Nov 1997 03:26:42 GMT Message-ID: <3474ab40.2923767@smtp-gw01.ny.us.ibm.net> References: <199711150553.QAA31140@godzilla.zeta.org.au> In-Reply-To: <199711150553.QAA31140@godzilla.zeta.org.au> X-Mailer: Forte Agent 1.01/16.397 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by hub.freebsd.org id SAA26702 Sender: owner-freebsd-hackers@freebsd.org X-Loop: FreeBSD.org Precedence: bulk On Sat, 15 Nov 1997 16:53:53 +1100, Bruce Evans wrote: >is approximately 8 ports saturated with 32 bytes of input, 32 bytes >of output and a modem status change. This takes about 2*32 + 1*32 + 5 >i/o's per port. Each i/o takes about 1 usec on an 8MHz ISA bus (perhaps >125 nsec more or less). Altogether, it takes about 8*101 = 808. usec. >Altogether, with saturated input and no output it takes at least about >8*37 = 296 usec. Where you say 2*32 + 1*32 +5, I thought you meant two I/O for each input byte and one I/O for each output byte. But later you say 37 (32 + 5) I/O for saturated input, which would mean only one I/O for each input byte, so now I wonder if you meant the opposite -- two I/O for each output byte and one I/O for each input byte. But that doesn't sound right -- don't I need to read bit 0 of the line status register before trying to read a byte from the receiver FIFO, so that I'll know when I've emptied the receiver FIFO? That would give two I/O per input byte. John