From owner-freebsd-hardware Sat Jun 29 08:30:48 1996 Return-Path: owner-hardware Received: (from root@localhost) by freefall.freebsd.org (8.7.5/8.7.3) id IAA09047 for hardware-outgoing; Sat, 29 Jun 1996 08:30:48 -0700 (PDT) Received: from genesis.atrad.adelaide.edu.au (genesis.atrad.adelaide.edu.au [129.127.96.120]) by freefall.freebsd.org (8.7.5/8.7.3) with ESMTP id IAA09033 for ; Sat, 29 Jun 1996 08:30:36 -0700 (PDT) Received: from msmith@localhost by genesis.atrad.adelaide.edu.au (8.6.12/8.6.9) id AAA21450; Sun, 30 Jun 1996 00:49:04 +0930 From: Michael Smith Message-Id: <199606291519.AAA21450@genesis.atrad.adelaide.edu.au> Subject: Re: muliport boards - building a PPP dialup server To: bde@zeta.org.au (Bruce Evans) Date: Sun, 30 Jun 1996 00:49:03 +0930 (CST) Cc: jparnas@jparnas.cybercom.net, msmith@atrad.adelaide.edu.au, Kevin_Swanson@BLaCKSMITH.com, bsdi-users@bsdi.com, hardware@FreeBSD.org, stesin@elvisti.kiev.ua In-Reply-To: <199606291101.VAA02125@godzilla.zeta.org.au> from "Bruce Evans" at Jun 29, 96 09:01:42 pm MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-hardware@FreeBSD.org X-Loop: FreeBSD.org Precedence: bulk Bruce Evans stands accused of saying: > > >FIFO. Neither are suitable for 512KBps; at this speed you have a new > >byte arriving every 16us, or a full FIFO after only 512usec. This is too > >fast for anything other than a dedicated system. > > That's not fast. A 386/20 can easily handle an interrupt every 86 us for > a full (1 byte :-) fifo on an 8250. The problem is to move the data > fast enough. 40 us every 512 us to move 32 bytes may be acceptable for > one port, but it won't work for 16 ports. It wouldn't surprise me for some other part of the system to block serial interrupts for 1/2msec or longer; FIFO overflows on a 16550 occur on occasion on an X workstation running at 38k4, ie. 4ms worth of FIFO. Hence the comment about a dedicated system. > Bruce -- ]] Mike Smith, Software Engineer msmith@atrad.adelaide.edu.au [[ ]] Genesis Software genesis@atrad.adelaide.edu.au [[ ]] High-speed data acquisition and (GSM mobile) 0411-222-496 [[ ]] realtime instrument control (ph/fax) +61-8-267-3039 [[ ]] Collector of old Unix hardware. "Where are your PEZ?" The Tick [[