Date: Sat, 18 Oct 1997 19:13:30 -0400 (EDT) From: Peter Dufault <dufault@hda.com> To: mdean@best.com (mdean) Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: Opinions wanted. Message-ID: <199710182313.TAA23016@hda.hda.com> In-Reply-To: <Pine.SGI.3.95.971018160306.9841A-100000@shellx.best.com> from mdean at "Oct 18, 97 04:06:48 pm"
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> If an 8255 (digital I/O) 8-bit port is opened via open() call by the user > as O_RDWR then it becomes an output, should I make all lines high, or all > lines low by default. I noticed that the 8255 seems to use low (but i have > set them high in my driver because the equipment I use outputs for is > activated by active low signal so I don't want it to all be turned on just > by opening the device file), what may I ask is more general all high, or > all low (in your opinion ofcourse)? You must pass the normal behavior of the hardware through to the software. The system design must arrange to pull the signals high at start up (if you can, yes I'm mostly software) so that it doesn't turn on devices. The hardware must be set up with pullup or pulldown resistors as appropriate to e.g. avoid turning on the natural gas solenoid in the oxygen tent at powerup in case the system hangs while trying to automatically connect to microsoft.com to download the latest browser. All systems may do this soon. Peter -- Peter Dufault (dufault@hda.com) Realtime development, Machine control, HD Associates, Inc. Safety critical systems, Agency approval
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