miket@bnrmtv.UUCP (Michael Thompson) (04/01/89)
Greetings fellow Unix PC'ers, I have recently been flipping through some back issues of BYTE magazine and I have come across two articles from Ciarcia's Circuit Cellar (May & June of 1986) which describe how to build a SCSI interface to his SB180 computer. What intrigued me is that he uses the NCR 5380 which is a single chip SCSI controller. It seems to me that this chip would be very easy to connect to the Unix PCs bus with minimal support chips. I believe that only some address decoding and interrupt interface chips would be needed. I admit that I have not looked at the schematics for the Unix PC, but I can't imagen AT&T (through Convergent) have done anything too bizzare to the bus to prevent hooking up the NCR 5380 in a relatively straight forward manner. What could be the greater unknown is the coding of a loadable device driver to control the SCSI controller chip. I have written a character based loadable driver for a Sun 386i before, but it operated on a relatively simple level and did not implement a protocal as complicated as the SCSI protocal. I also understand that block oriented device drivers are more complicated to write too. It also may be desireable to make a more complicated type interface circuit where buffer memory is used and the Unix PC be able to perform DMA transfers into that buffer memory and the NCR 5830 transfer to and from that memory. This will keep the SCSI interface chip from constantly yanking on the Unix PC bus interrupt to request more data. I would encourage anyone interested in perhaps joining forces to build as SCSI interface, read the Circuit Cellar articles from the May and June issue of BYTE magazine and see if they also think that it would be possible to adapt the SCSI controller for use on the Unix PC. I would also appreciate it if anyone could point me to a good reference source on the SCSI protocal since these articles were a little skimpy in these areas. These articles are also available in Volume VI of Ciarcia's Circuit Cellar book. I think that building a SCSI board based on this chip would be a 4 on a scale of 1 to 10 in difficulty and writing a SCSI block device driver would be a 8 or 9 on a scale of 1 to 10. What do you think? I'm I crazy and dreaming of pie in the sky or is there a possibility that I (or we) could pull it off. I am pretty handy at building prototype digital hardware and even better at coding, I just don't have access to all the information to really tell if a SCSI adapter board would be beyond my modest abilities. I can envision a few of us hardware types communicating together to come up with a SCSI interface card which could be prototyped and then a few of us software types communicating and coming up with a workable device driver. Once we got a working prototype (hopefully more than one) we could release all the information to the Unix PC community so anyone would be able to build such a device. Am I really thinking crazy here or not. The ultimate goal would be to have a SCSI board which could be attached to commonly available SCSI hard drives and tape drives. I welcome any comments. Just as long as they don't recommend that I be hauled away in a straight jacket. Mike Thompson ========================================================================= Michael P. Thompson Bell Northern Research Member Scientific Staff 685A E. Middlefield Road (415) 940-2575 Mountain View, CA amdahl!bnrmtv!miket 94039-7277
jbm@uncle.UUCP (John B. Milton) (04/10/89)
In article <5179@bnrmtv.UUCP> miket@bnrmtv.UUCP (Michael Thompson) writes:
[suggests construction of a SCSI board for the UNIXpc]
I guess I should chime in here. There is a person, John Lydic, who is NOT on
the net, who IS building a SCSI/memory/8 serial Mondo Combo card for the
UNIXpc. He has build 2 or 3 SCSI interfaces and written drivers for OS/9. He
is quiet a ways along, but still has a ways to go. I will try to get some up
to date information when I get back from Comdex.
As far as my board goes, all the proto hardware works fine, I have parts to
build 10 board. I skipped the PC proto step, and order 50 boards from Saturn
in MI. I expect them to be here next week. I am STILL shooting for having at
least some boards at Trenton, April 22 & 23.
John
--
John Bly Milton IV, jbm@uncle.UUCP, n8emr!uncle!jbm@osu-cis.cis.ohio-state.edu
(614) h:294-4823, w:764-2933; AMPR: 44.70.0.52; Don't FLAME, inform!