Date: Sun, 30 Jun 1996 23:42:33 -0400 From: "Jacob M. Parnas" <jparnas@jparnas.cybercom.net> To: Michael Smith <msmith@atrad.adelaide.edu.au> Cc: chuckr@glue.umd.edu, Kevin_Swanson@blacksmith.com, freebsd-hardware@freebsd.org Subject: Re: muliport boards - building a PPP dialup server Message-ID: <199607010342.XAA15914@jparnas.cybercom.net> In-Reply-To: Your message of Sat, 29 Jun 1996 16:49:40 %2B0930. <199606290719.QAA20648@genesis.atrad.adelaide.edu.au>
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In message <199606290719.QAA20648@genesis.atrad.adelaide.edu.au>you write: >Jacob M. Parnas stands accused of saying: >> >> These days, a multiboard should at least do 115200baud in my opinion. At >> least it can be competitive with modems. 8x115200baud is still only 1/8 >> MB/sec and 16x115200 is only 1/4 MByte/sec. Not exactly fast. > >Fast has nothing to do with it. Interrupt rates do. What's important to most people is to maximize performance at a minimum price. Handling interrupts quickly is one way to keep a fifo empty. People would never no the difference if the fifo was emptied every 1/5000 of a second or every 1/100 of a second. As long as the latency time wasn't too long and throughput wasn't comprimised and the CPU wasn't overloaded. >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. > >> Jacob Its true that there's a lot of wasteage. If while I was in school early on and sharing a class computer with 4MB RAM on a VAX 11/780 that I would feel I needed to upgrade a 64 MB 20 MIPS sparc 2 that I had to myself, I'd say you were crazy. But that's what I'm doing. But while the trivia may be interesting, what I'm interested in is the bottom line, like most people. If I were designing IO cards things would be very different. But if you read everything about things that aren't important to what you do, you'll not be that good at what you do. Its OK to have hobbies, but choose them carefully. Its like if my car breaks. I don't know how to fix it for anything major. So I call an expert (mechanic). If I were to spend time learning to all type of car problems, Refrigerator problems, sink problems, I'd lose precious time and the cost of learning it would be > than working on computers and paying to have those other things fixed. Jacob >-- >]] 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 [[
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