Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!usc!apple!oliveb!tymix!tardis!jms
From: jms@tardis.Tymnet.COM (Joe Smith)
Newsgroups: comp.sys.amiga.tech
Subject: Re: DMA in VM
Summary: Use virtual addresses for the devices
Message-ID: <838@tardis.Tymnet.COM>
Date: 1 Dec 89 03:49:31 GMT
References: <14059@grebyn.com>
Reply-To: jms@tardis.Tymnet.COM (Joe Smith)
Organization: BT Tymnet, San Jose, CA
Lines: 16

In article <14059@grebyn.com> ckp@grebyn.UUCP (Checkpoint Technologies) writes:
>	If the DMA controller hardware can't handle discontiguous IO
>buffers, then they must DMA into a contiguous buffer and CPU-copy the
>results to the task buffer. This would be a big win for non-DMA
>controllers, which would not need this intermediate RAM buffer.

There's an alternative you've overlooked.  Add another MMU just for DMA.  A
single MMU could be shared amoung several DMA devices and let them all think
they were doing I/O to contiguous addresses.  There's no need to bother the
CPU or need contiguous RAM if you can fake it.  (The VAX and other systems
do just this.)
-- 
Joe Smith (408)922-6220 | SMTP: JMS@F74.TYMNET.COM or jms@gemini.tymnet.com
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