From owner-freebsd-hackers Thu Mar 21 02:44:05 1996 Return-Path: owner-hackers Received: (from root@localhost) by freefall.freebsd.org (8.7.3/8.7.3) id CAA18004 for hackers-outgoing; Thu, 21 Mar 1996 02:44:05 -0800 (PST) Received: from hda.com (hda.com [199.232.40.182]) by freefall.freebsd.org (8.7.3/8.7.3) with SMTP id CAA17936 for ; Thu, 21 Mar 1996 02:43:59 -0800 (PST) Received: (from dufault@localhost) by hda.com (8.6.11/8.6.9) id FAA13688; Thu, 21 Mar 1996 05:43:28 -0500 From: Peter Dufault Message-Id: <199603211043.FAA13688@hda.com> Subject: Re: real time interrupts in FreeBSD? To: bde@zeta.org.au (Bruce Evans) Date: Thu, 21 Mar 1996 05:43:27 -0500 (EST) Cc: hackers@FreeBSD.org, pst@shockwave.com Reply-To: hdalog@zipnet.net In-Reply-To: <199603210513.QAA22241@godzilla.zeta.org.au> from "Bruce Evans" at Mar 21, 96 04:13:18 pm X-Mailer: ELM [version 2.4 PL24] Content-Type: text Sender: owner-hackers@FreeBSD.org X-Loop: FreeBSD.org Precedence: bulk > > - FreeBSD isn't a real time system. You have to be prepared to deal with > a worst-case interrupt latency of 20 msec even on a P133 or do more > work to minimise the latency. (I'm still trying to track down what > causes a 5 (?) msec clock interrupt latency. I found what caused 20+ > msec clock interrupt latency. It was a local experiment that that > sometimes increased clock interrupt latency to softclock interrupt > latency.) To address this make sure you have a way to measure your latency. When I last played with this I used a conversion overrun on a clocked A-D board as a "missed deadline" flag, restarting the conversion in the real time tick. This was real easy - I'm sure you can also do this using clock with more work. Hopefully latency hasn't gotten much worse in the last few years - I guess I'll find out soon. BTW: With 20 msec latency how can we can keep up with 115200 input data? We're receiving about 240 characters in 20 msec at that rate. -- *** March 13, 1996: Our ISP may be GONE. You may never read this. *** *** "hda.com" connectivity is now intermittent to nonexistent *** Peter Dufault Real-Time Machine Control and Simulation HD Associates, Inc. Voice: 508 433 6936 dufault@hda.com Fax: 508 433 5267