Date: Tue, 27 Aug 1996 11:52:10 -0500 From: Hal Snyder <hal@post.vale.com> To: Koshy <koshy@india.hp.com>, "'Terry Lambert'" <terry@lambert.org> Cc: "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org> Subject: SCSI vs IDE (was: Multiple swaps...) Message-ID: <01BB940E.2E62F1F0@jaguar>
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Terry Lambert wrote: > I was under the impression that probing the chipset for this capability [DMA] > will crash older chipsets. Thus it is impossible to probe for the > capability uniformly and safely, other than by keeping a ROM/ID table > and using that to detect the things. Windows95 and NT get around the > issue by logging probes during install. If a user resets after an "if > this takes too long..." message, it decides the hardware isn't there > when the install starts up again (what the hell is "too long"? ...they > don't tell us). What about DMA on working IDE controllers? Is it the same kind of DMA as on high end SCSI controllers? Correct me if I'm wrong here (have been away from kernel and driver hacking a couple years), but Adaptec uses "First Party" or "Bus Mastering" DMA - which is allegedly better than "Third Party" DMA going through the DMA controller on the motherboard. Feel free to provide details here, guys! Not all SCSI controllers are alike. I wrote a unix device driver for the old Seagate/Future Domain SCSI controllers. They were basically a parallel port, so you had to do most of the SCSI protocol in software. I never did get "asynchronous" mode to work reliably, i.e. start an i/o transfer on one device, disconnect, start another transfer on a second device, etc. I suspect that the SCSI controllers that appeared glued onto sound boards a couple years ago were equally nasty. [I changed the subject of the thread. A defect of the mailing list system is that the title propagates forever while the discussion wanders from memory wait states to demon plushies...]
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