Date: Thu, 30 Mar 1995 08:03:33 -0500 (EST) From: Peter Dufault <dufault@hda.com> To: roberto@blaise.ibp.fr (Ollivier Robert) Cc: olsenc@ichips.intel.com, hardware@FreeBSD.org Subject: Re: Questions about NCR PCI SCSI driver Message-ID: <199503301303.IAA02568@hda.com> In-Reply-To: <9503292241.AA23880@blaise.ibp.fr> from "Ollivier Robert" at Mar 30, 95 00:41:18 am
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Ollivier Robert writes: > > > I asked this before. It seems as though I have to ask each question twice > > to get an answer from this group. > > Hmmm, this is the first time I see this question. > > Anyway : > > > Will performing certain SCSI operations in FreeBSD (say tape rewind) cause the > > SCSI bus to hang until completion? People have complained about this in > > Linux because the driver is not polished. Hopefully, someone who uses this > > device can testify that things are working ok or not. > > If the SCSI bus was hung during rewind I'd have noticed as I have only > SCSI devices... No bus hang down here. The SCSI bus would only hang if you don't allow disconnects and specified the "immediate" bit in the rewind command as 0 so that the tape didn't return until the rewind was complete. You can set up your host adapters so that they won't let a device disconnect, if you have a 1542C look on the setup screen and you'll find a place you can prevent a device from disconnecting. This will give the SCSI bus hang behavior we don't want. When you tell the tape to rewind the command usually won't return until the tape is rewound, but the bus should be free. Are you sure about this in Linux? It is hard for me to figure out how they could consistently arrange such bad behavior across all host adapters. Maybe the driver won't take other commands? That seems easier to get consistently wrong but pretty far fetched. > > I don't see why there must be a hang either. You send the command to the > device and that's all (at least to my understanding of SCSI operations). I wish this were true. Basically you issue the command and if it will take a while the device disconnects and later reconnects when ready to supply the results of the command. Unfortunately some of these devices out there are designed for BDDB (brain dead dos boxes) and do stupid things. The standard firmware in the Microtek Scanner, again, will not disconnect while it is scanning. This means it will hold up the SCSI bus while it moves the scanner across a one inch band and then finally sends up the data. Peter -- Peter Dufault Real Time Machine Control and Simulation HD Associates, Inc. Voice: 508 433 6936 dufault@hda.com Fax: 508 433 5267
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