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From: j@uriah.sax.de (J Wunsch)
Newsgroups: comp.os.386bsd.development
Subject: Re: [FreeBSD 1.0R] DMA Problems?
Date: 17 Jan 1994 13:18:58 +0100
Organization: Private U**X site; member IN e.V.
Lines: 63
Message-ID: <2hdvniINN1mu@bonnie.sax.de>
References: <CHCErs.G5w@genesis.nred.ma.us> <2dj25i$1ga@u.cc.utah.edu> <2encotINN3sq@bonnie.sax.de> <2eqjt7$dqm@u.cc.utah.edu> <CI6291.HBA@genesis.nred.ma.us> <2fbvtoINNk71@bonnie.sax.de> <jmonroyCIJFAr.Atn@netcom.com> <2g4kjvINNnsf@bonnie.sax.de> <jmonroyCJ3ts3.1Ls@netcom.com> <2gk4fjINNal@bonnie.sax.de> <jmonroyCJB69t.D8B@netcom.com> <2gumo6INNi85@bonnie.sax.de> <jmonroyCJIroC.6AG@netcom.com>
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jmonroy@netcom.com (Jesus Monroy Jr) writes:

>	Can I clear this up by sending you a copy of the
>	page in the IBM technical reference where "what I assume"
>	is stated?

Though i don't own any IBM box, yes, you can... As long as it ain't more
thant say 20 KB. I'm only uucp-connected and have to pay real money for
each byte. (That's why i hate your indented text. Band width without any
information at all.)

>	OK... in English then, you disabled the controller
>	chip, via the Command REgister ..

>	 the DMA refresh is a psuedo operation.
>	meaning that it does not do a read or a write -
btw., it does a read, but throws away the byte read
>	- simply a strobe of the address line.

Yes. But it will have to initiate a bus cycle to do this. If i'm disabling
my DMA controller, it cannot initiate anything. So it's irrelevant whether
this is a dummy operation or not. The term ``dummy'' only refers to the
fact here that there is no data transferred. But not to the fact the DMA
would not be needed anymore. If i kill any DMA operation, i would also
kill the dRAM refresh if it were done by DMA.

>: I've stated all the results of my test. (DMA fails, but RAMs are okay.)
>:
>	No, what you stated were the conclusions of your test.

What else results did you expect?

>	I think you're being stubborn or lazy.

The latter, definately.

>: I can
>: simply stop it with some out's from my debugger. 
>:
>	I don't think your serious.

Why not? Any good debugger might be much more helpful than tons of code
lines. I would never have completed my old CP/M floppy driver without
extended tests run through a debugger. (The only thing on floppies that
cannot be done by a debugger is sector read/write, since it implies tight
timing conditions. Everything else, up to a READ SECTOR ID can be done
with a debugger.)

>: DMA channel 0 is not wired to the IO bus, thus it is only available for
>: mainboard chips (if there are any).
>:
>	Wait a minute... here in a previous article you stated 
>	that some (support) boards can use DMA channel 0!!

Aeh, well, i should have looked into that old magazine... But sorry, i
don't have the time for it, and i think it wouldn't bring us any millimeter
closer to a solution of our DMA overrun problem.

-- 
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.''