*BSD News Article 25045


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Path: sserve!newshost.anu.edu.au!munnari.oz.au!news.Hawaii.Edu!ames!agate!howland.reston.ans.net!vixen.cso.uiuc.edu!uxa.cso.uiuc.edu!rkb55989
From: rkb55989@uxa.cso.uiuc.edu (Rafal Boni)
Newsgroups: comp.os.386bsd.development
Subject: Re: [FreeBSD 1.0R] DMA Problems?
Date: 16 Dec 1993 04:48:30 GMT
Organization: University of Illinois at Urbana
Lines: 39
Message-ID: <2eopau$hde@vixen.cso.uiuc.edu>
References: <CHCErs.G5w@genesis.nred.ma.us> <2dj25i$1ga@u.cc.utah.edu> <2encotINN3sq@bonnie.sax.de>
NNTP-Posting-Host: uxa.cso.uiuc.edu

j@uriah.sax.de (J Wunsch) writes:

[stuff J"org and Terry were debating deleted...]

>In fact, i'm also experiencing lotta DMA overruns when attempting to do
>some floppy IO while some heavy compile job is running. This is in a box
>with an Adaptec SCSI, and i didn't track it down whether it's the CPU
>load that causes the trouble (would really look strange to me), or if
>it's the heavy disk IO that happens while compiling.


	I would be tempted to say that the Adaptec is at fault... I have a 
	3Com 3c507 Ethernet card in my machine, and the docs SPECIFICALLY
	mention the fact that Adaptec's 154x may cause problems for the
	Ethernet card's DMA reads/writes....  Later 3Com updated some of
	the [I would guess] DMA related circuitry to be able to handle longer
	timeouts or something of that nature... 

>Assuming it's the latter, so it could be some problem with the host adaptor
>DMA cycles - does the adaptec really care for other DMA requests floating
>around on the bus while it is considering to take over the bus?

	See above.... I'd say if other vendors have had trouble with it, then
	you might also.... BTW, are you not using the Adaptec's floppy 
	controller? [It would be mighty strange if the 1542 was trashing it's
	own floppy controller's DMA requests ;>]

>As a workaround, Serge Vakulenko proposed to simply ignore the DMA overrun
>error and retry the transfer until it succeeds (or some other error occurs).
>-- 
>in real life: J"org Wunsch |   )  o o  | primary: joerg_wunsch@tcd-dresden.de
>above 1.8 MHz:   DL 8 DTL  |    )  |   | private: joerg_wunsch@uriah.sax.de
>                           | . * ) ==  |
>          ``An elephant is a mouse with an operating system.''

 ----------------------------------------------------------------------------
Rafal Boni   I'm a student -- nothing I say holds any value!   r-boni@uiuc.edu
	This message has not been endorsed by the Surgeon General, nor
	the University of Illinois.  All opinions are my own, not UIUC's.