Article View: comp.sys.amiga.tech
Article #2461Re: DMA in VM
From: Joe Smith
Date: Fri, 01 Dec 1989 03:49
Date: Fri, 01 Dec 1989 03:49
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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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Path: arc1-ca.pugleaf.net!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