[robespierre]

What if we assume that the AM33C93A is not buggy, but that it conforms to the standards in place at the time it was designed? In 1989, the latest standard was SCSI-1 with the CCS (Common Command Set). After 1991, the SCSI-2 standard was in place, and the ST118273N is a SCSI-3 drive produced in 1998. That's a time span of a decade during which major changes were made to the SCSI protocol.

Some of the differences between SCSI-1/CCS and SCSI-2 are:

1. Several options were removed from SCSI-1:

a. Single initiator option was removed.
b. Non-arbitrating Systems option was removed.
c. Non-extended sense data option was removed.
d. Reservation queuing option was removed.

e. The read-only device command set was replaced by the CD-ROM command set.
f. The alternative 1 shielded connector was dropped.

2. There are several new low-level requirements in SCSI-2:
a. Parity must be implemented.
b. Initiators must provide TERMPWR — Targets may provide TERMPWR.
c. The arbitration delay was extended to 2.4 us from 2.2 us.
d. Message support is now required.

(source: Dal Allan in Computer Technology Review, Jan 1991)

In thinking about how any of these differences could cause a timeout, note that parity and arbitration are related (parity must be correctly asserted during the selection phase for the target to respond). A SCSI-3 drive may not have been designed and tested with HBAs more than a decade older and conforming to a standard 2 major versions older.

I installed the MMI-210 ("Vigra") board in VME-slot 1. Then in slot 2, whilst jumpering the IACK and BG jumpers of slot 1, leaving open the IACK/BG jumpers in slots 2-4. In both cases I get in HINV only:

That's backwards. The jumpers provide grant continuity across empty slots. When a slot is occupied, its corresponding jumpers must be removed. When a slot is empty, the jumpers are installed so that the Bus Grant and Interrupt Acknowledge lines can pass over the empty connector.