*BSD News Article 26960


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From: bad@flatlin.ka.sub.org (Christoph Badura)
Subject: Re: Late comments on the DMA problem.
Date: Sat, 5 Feb 1994 19:41:29 GMT
Message-ID: <CKro16.JBM@flatlin.ka.sub.org>
References: <1994Jan24.103912.8591@cc.usu.edu> <940131281@rwsys.wimsey.bc.ca> <jmonroyCKLDAu.CK@netcom.com>
Organization: Guru Systems/Funware Department
Lines: 27

In <jmonroyCKLDAu.CK@netcom.com> jmonroy@netcom.com (Jesus Monroy Jr) writes:
>Randy Wright (rw@rwsys.wimsey.bc.ca) wrote:
>: ivie@cc.usu.edu () writes:
>: > In article <jmonroyCK2t6n.1pM@netcom.com>, jmonroy@netcom.com (Jesus Monroy Jr) writes:
>: > > ivie@cc.usu.edu wrote:
>: > > : Since you can't get an interrupt to tell you that the DMA controller has
>: > > : finished doing a page, you can't reload the DMA addresses when the end of
>: > > : a page is reached.
>: > > 	please define page. your message is ambiguous.
>: > Page = virtual memory page. I'm most familiar with the VAX, where a page
>: > is 512 bytes; I don't know how big it is on these newfangled 386 thingies.
>: 386 virtual memory paging deals in 4-kb pages.
>	Can you please define this 4-kb page a bit more with a qualifier?

The definition of page is completely irrelevant since you can't get an
interrupt from the DMA controller when it finishes a page of any size.
The point is that the DMA controller knows zilch about pages, so you
can't get him to do something when he's finished with a page he
doesn't know about.

Anyone how thinks the DMA controller would know anything about the
MMU's pages is simply not competent enough to discuss DMA issues.
-- 
Christoph Badura	bad@flatlin.ka.sub.org		+49 721 606137

Es genuegt nicht, keine Gedanken zu haben;
man muss auch unfaehig sein, sie auszudruecken.  - Karl Kraus