Date: Thu, 21 Mar 1996 05:43:27 -0500 (EST) From: Peter Dufault <dufault@hda.com> To: bde@zeta.org.au (Bruce Evans) Cc: hackers@FreeBSD.org, pst@shockwave.com Subject: Re: real time interrupts in FreeBSD? Message-ID: <199603211043.FAA13688@hda.com> In-Reply-To: <199603210513.QAA22241@godzilla.zeta.org.au> from "Bruce Evans" at Mar 21, 96 04:13:18 pm
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> > - 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
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