home *** CD-ROM | disk | FTP | other *** search
- Path: sparky!uunet!auspex-gw!guy
- From: guy@Auspex.COM (Guy Harris)
- Newsgroups: comp.arch
- Subject: Re: question about DMA devices
- Message-ID: <16042@auspex-gw.auspex.com>
- Date: 22 Dec 92 22:25:45 GMT
- References: <1992Dec18.175402.27841@hubcap.clemson.edu> <JAN.92Dec22183354@pallas.neuroinformatik.ruhr-uni-bochum.de>
- Sender: news@auspex-gw.auspex.com
- Organization: Auspex Systems, Santa Clara
- Lines: 13
- Nntp-Posting-Host: auspex.auspex.com
-
- >So this is quite an old trick, and not really that difficult to do. I would
- >assume that current Unix/workstation systems do something similar.
-
- Well, it's what Suns do. Suns with "Sun-style" static RAM MMUs use the
- MMU as a bus map - addresses on the I/O bus get run through the MMU
- (after having, e.g. 0xFF stuck in as the top byte) to get the physical
- address to which they refer. Some, perhaps all, Suns with
- in-memory-page-table MMUs have separate "I/O MMUs" for that purpose (the
- 3/80 and 3/4xx, which used the 68030's MMU as the main MMU, did, as do
- the SPARC Reference MMU machines, or at least the Sun-4m machines; dunno
- about the 386i).
-
- Other UNIX boxes may or may not do that.
-