The first VAX to have a SCSI port was the KA410 BabyVAX. It is an NCR 5380. However, DEC stupidly refused to support it as a SCSI port and used it for only one special tape drive. KA410 was succeeded by KA42/41, which also has an NCR 5380 SCSI port (two of them actually). The NCR 5380 SCSI hardware on KA410 and KA42/41 is virtually identical, but DEC supported SCSI only on KA42/41 and not on KA410. Ultrix has two different drivers for NCR 5380, named stc and scsi. The former supports the tape drive usage of the SCSI bus, and the latter supports normal usage. The decision as to which one to use is based on the CPU type alone. (Ultrix doesn't use a virtual bus umbrella for on-board devices, instead they are probed and attached right from kaXXX.c modules. In the case of NCR 5380, ka630.c, which handles KA410, probes and attaches the stc driver, and ka420.c, which handles KA42/41, probes and attaches the scsi driver. As you've surely noticed, DEC's naming and organization of kaXXX.c source files is anything but obvious, and the correspondence between these files and actual CPUs and their names is anything but direct.)

I totally and completely disagree with DEC's idiotism in this area, and I also want to support some SCSI ports that Ultrix never supported at all (NCR 53C94 based ones), so with 90% probability I won't use Ultrix's SCSI code and will write my own instead. A lot of sources suggest that the special tape drive that DEC supported on KA410 is just a normal SCSI tape drive fixed at SCSI ID 1 and terminated inside the box so that the user doesn't see DEC's dirty work. This means that one can ignore DEC's idiotism and support normal SCSI only, and the special tape drive will work just fine.

This page has been last updated on 16-MAY-1999.

@(#)scsi.html 1.1 03/12/18

Michael Sokolov
[email protected]