From owner-freebsd-hardware Sat Jun 29 03:46:07 1996 Return-Path: owner-hardware Received: (from root@localhost) by freefall.freebsd.org (8.7.5/8.7.3) id DAA23708 for hardware-outgoing; Sat, 29 Jun 1996 03:46:07 -0700 (PDT) Received: from hda.com (ip86-max1-fitch.zipnet.net [199.232.245.86]) by freefall.freebsd.org (8.7.5/8.7.3) with SMTP id DAA23703 for ; Sat, 29 Jun 1996 03:46:03 -0700 (PDT) Received: (from dufault@localhost) by hda.com (8.6.11/8.6.9) id GAA03826; Sat, 29 Jun 1996 06:34:55 -0400 From: Peter Dufault Message-Id: <199606291034.GAA03826@hda.com> Subject: Re: muliport boards - building a PPP dialup server To: msmith@atrad.adelaide.edu.au (Michael Smith) Date: Sat, 29 Jun 1996 06:34:55 -0400 (EDT) Cc: jparnas@jparnas.cybercom.net, chuckr@glue.umd.edu, Kevin_Swanson@BLaCKSMITH.com, freebsd-hardware@FreeBSD.org In-Reply-To: <199606290719.QAA20648@genesis.atrad.adelaide.edu.au> from "Michael Smith" at Jun 29, 96 04:49:40 pm Reply-to: hdalog@zipnet.net X-Mailer: ELM [version 2.4 PL24] Content-Type: text Sender: owner-hardware@FreeBSD.org X-Loop: FreeBSD.org Precedence: bulk > Fast has nothing to do with it. Interrupt rates do. > > You should sit down and read some of the stuff that Bruce Evans has posted > on the subject over the years; most particularly his analysis of where the > actual load in handling serial ports comes from. Some key points : > > - A 486 can service around 40,000 ISA interrupts per second, assuming > minimal interrupt processing time. > - Most of the CPU overheard in handling serial in/output is in the tty > layer. As you know once you're in the interrupt routine it will check all ports, meaning that in the special case of input streaming in on multiple ports you will have a big reduction in interrupt load. I second looking up some of Bruce's postings. Now a few caveats I should have included in my last message about four ports continuous at 115200, since it doesn't translate over to general usage. I'm using my own software in a dedicated environment. I had to look in the driver to find the "right" settings of TTY flags to get a fast path through the driver, and I'm wondering if I'll have to tweak things when I upgrade the OS. The data is only coming in - nothing is going back out again. I can't vertically scroll an Xterm with the serial mouse without dropping input on the streaming data during a test session. If we were to double the size of the test stand to 8 devices I'd take a page from Henry's book and dedicate a small 486 to collect the data and then send it to the analysis system over ethernet. However, it is actually five ports at 115200, since we have a debug port running the same software to the same type of device that we think nothing of using during a collection sequence. And I sometimes establish a PPP link at 57.6 on a modem control line while the testing is going on. The overhead on the system is not dramatic - you don't notice that anything is going on other than the "xterm scroll" problem. We stay in X, leave drives NFS exported, etc. -- Peter Dufault Real-Time Machine Control and Simulation HD Associates, Inc. Voice: 508 433 6936 dufault@hda.com Fax: 508 433 5267