Date: Fri, 14 Apr 1995 11:38:55 -0400 (EDT) From: Peter Dufault <dufault@hda.com> To: freebsd-hackers@FreeBSD.org Cc: freebsd-scsi@FreeBSD.org Subject: SCSI target Message-ID: <199504141538.LAA00581@hda.com>
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I've added a SCSI target device. Using this you can act as a target and another system acting as an initiator can send data to you over the SCSI bus. However, the only host adapter that supports this is the Adaptec 1542B. The 1542C will hang the bus big time if you put it into target mode, so I've locked it out. I have little hope that most of the commercial firmware will support this properly, so if some of our firmware crankers want to start cranking firmware they can look at the isa/aha1542c to get a feel for how it should act. I'll have a Acculogic board with the NCR 825 in house for a while. Basically there is an escape added to put the host adapter in target mode. Once it is in target mode it must respond to the mandatory commands: INQUIRY, REQUEST SENSE, SEND DIAGNOSTIC and TEST UNIT READY as well as the two data transfer commands SEND DATA and RECEIVE DATA. The 1542 model is good, and I suggest we just use that as much as possible. You can set up a data transfer in advance, with information that indicates which initiator it is for, and then when that initiator connects the board does the transfer. If an initiator connects to the 1542 when it doesn't have a transfer set up for that initiator, the 1542 will disconnect, generate a device interrupt, and report the ID and LUN of the initiator that connected as well as the amount of data the initiator wants to transfer. Eventually I'd like to add support for reserving units on the SCSI bus, sharing read only disk partitions, and running TCP/IP over SCSI using target mode capable host adapters. I think that could make for a nice little cluster. -- 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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