Is The M9312 Boot Module Essential?

[Fritz Mueller]

> On Feb 19, 2022, at 10:51 AM, Noel Chiappa via cctalk <cctalk at classiccmp.org> wrote:
> The -11/34 (not the /34A) has something unusual for grant timeouts, but I
> forget the details. I'll look it up.

> On Feb 19, 2022, at 12:11 PM, Fritz Mueller <fritzm at fritzm.org> wrote:
> I just did an 11/34 restoration last year, so this is fresh in mind — I think you are thinking of the M9302, Noel: a far-side terminator card with integrated SACK turnaround?

A few additional details, in case it is helpful:

IIRC, the 11/34 doesn’t have SACK timeout implemented in the CPU cards (the /34A did add this, however.)  So without an M9302 on the far end of the bus, the CPU could hang in a situation with an unacknowledged grant (which I think would be somewhat rare, but possible).  I believe it is possible to boot an 11/34 at least as far as a ROM boot monitor with a non-SACK (M930 or such) terminator on the far side.

An 11/34 with a M9302 SACK terminator _will_ hang, though, with a broken grant chain — the floating grant will trigger the M9302 to continuously assert SACK locking the bus.  “Better” CPUs, which used SACK timeout instead of turn-around, were more robust this way.

Incidentally, I think the 11/34 was contemporaneous with, and usually found with, the slightly earlier M9301 ROM terminator on the near side, rather than the later M9312, though both should work fine.

    cheers,
        —FritzM.