From owner-freebsd-hackers Sat Feb 3 19:27:59 1996 Return-Path: owner-hackers Received: (from root@localhost) by freefall.freebsd.org (8.7.3/8.7.3) id TAA21478 for hackers-outgoing; Sat, 3 Feb 1996 19:27:59 -0800 (PST) Received: from genesis.atrad.adelaide.edu.au (genesis.atrad.adelaide.edu.au [129.127.96.120]) by freefall.freebsd.org (8.7.3/8.7.3) with ESMTP id TAA21466 for ; Sat, 3 Feb 1996 19:27:56 -0800 (PST) Received: from msmith@localhost by genesis.atrad.adelaide.edu.au (8.6.12/8.6.9) id MAA02867; Sun, 4 Feb 1996 12:13:00 +1030 From: Michael Smith Message-Id: <199602040143.MAA02867@genesis.atrad.adelaide.edu.au> Subject: Re: Watchdog timers (was: Re: Multi-Port Async Cards) To: bde@zeta.org.au (Bruce Evans) Date: Sun, 4 Feb 1996 12:12:59 +1030 (CST) Cc: msmith@atrad.adelaide.edu.au, phk@critter.tfs.com, hackers@FreeBSD.org, jgreco@brasil.moneng.mei.com In-Reply-To: <199602031341.AAA16215@godzilla.zeta.org.au> from "Bruce Evans" at Feb 4, 96 00:41:27 am MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-hackers@FreeBSD.org Precedence: bulk Bruce Evans stands accused of saying: > > Actually I don't have the data sheet and haven't seen it for a few years. > I seem to remember that there is an 8254 feature (automatic latch?) that > we should be using. Ah, sorry. Yes, you can latch any selection of the counters and then read them back at leisture. > Can you easily latch multiple 8254 counters at once in hardware? I think > it would work to put them at the same address for writes and at different > addresses for reads. Um, remapping the addresses for the 8254 would be very messy. Basically you have a control register and three data registers, one for each counter. To perform a readback of, say the first two counters, you would write an appropriate Counter Latch command to the command register, and then read back LSB and MSB from each of the counter data registers. > Is the slowness only the usual slowness for multiple 8-bit reads? Yes. I can't vouch for the 8254 at bus speeds of more than 10MHz though, but on a standard 8MHz bus it should be fine. > 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 [[ ]] "wherever you go, there you are" - Buckaroo Banzai [[