*BSD News Article 25578


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Newsgroups: comp.os.386bsd.development
Path: sserve!newshost.anu.edu.au!munnari.oz.au!bunyip.cc.uq.oz.au!harbinger.cc.monash.edu.au!yeshua.marcam.com!usc!howland.reston.ans.net!cs.utexas.edu!convex!seas.smu.edu!utacfd.uta.edu!rwsys!hammy!gordon
From: gordon@sneaky.lonestar.org (Gordon Burditt)
Subject: Re: [FreeBSD 1.0R] DMA Problems?
References: <jmonroyCIHJA2.oy@netcom.com> <jmonroyCIo4yD.1G5@netcom.com> <2fnapb$6eb@u.cc.utah.edu> <jmonroyCIvwpv.8F3@netcom.com>
Organization: /usr/lib/news/organi[sz]ation
Date: Tue, 4 Jan 1994 12:17:26 GMT
Message-ID: <CJ3u5H.9JG@sneaky.lonestar.org>
Lines: 28

>	To clarify the issue: DMA DRAM refresh skipping would be a 
>	bad term to use.   What happens is the timer for channel 0,
>	the DRAM refresh timer, is reprogrammed so that there are 

Timer 0 is the DRAM refresh timer?  Not on my system.  
(Timer 0 = timer interrupt, Timer 1 = refresh, Timer 2 = speaker)

>	It is possible, via software, to reprogram the refresh cycle.
>	My example program does this.  The results are had when the
>	system crashes.  That is, to make this a software *probe*
>	the program would (if it existed for *BSD) slowly turn down
>	the timer till the system crashed.  At this point, some

The proper way to do this is to test this while operating the environmental
controls to extremes of temperature and power supply voltages, and using
lots of patterns in RAM.  Oh, your system doesn't have controls like that?  
This probe routine would likely take an hour to run an adequate test even 
at ONE set of temperatures and power supply voltages.  That's a long time
to boot.  Sure, you can probably do it a lot faster if you have expensive 
analog measuring equipment attached to the system, but you don't.  Also, 
remember that refresh failure doesn't guarantee a crash.

Even if you test it properly, when it becomes known that your OS fiddles
with refresh this way, you can be sure that the reaction when you come to 
a DRAM manufacturer and say "bad RAM", they'll start laughing.  

						Gordon L. Burditt
						sneaky.lonestar.org!gordon