4 Feb
2019
4 Feb
'19
6:59 p.m.
On 02/04/2019 11:20 AM, Fritz Mueller via cctalk wrote:
This could be messy, but DEC was FAIRLY good at making
updates backwards compatible where possible. So, it MAY be
true that a later MMU will still work in this CPU.
Jon
The MMU classifies the error in register SR0; this decodes to a segment length error
(access within the segment beyond configured bound). As Noel notes, however, this is not
consistent with the instructions we see at the point of fault.
OK, so the CPU
presents an address that is within the
segment bound, but the MMU declares it to be OUTSIDE the
bounds of the segment. That could be a CPU problem, but
likely would be the same with the MMU on or off, so the
diags SHOULD catch that. But, if the CPU is sending a good
address, then it has to be the MMU is failing on the
addition/comparison with the segment size.
Anyway, is it
possible to borrow an MMU from somebody else?
Potentially... It is a two board
option; I do have a spare for both of the boards, but these spares each are in need of
other repairs at the moment.
One slightly complicating factor is that I have a *very* early 11/45. Most of my boards
(including the MMU boards), as well as my backplane, pre-date the currently available
schematics on bitsavers, etc., and there are no records regarding which ECOs have been
applied on my hardware. Thus my interest in tracking down ECOs/FCOs... I've been
picking my way through the list that Jay recently posted, verifying by looking at the
greenwires which FCO's I have applied and which not. Its a bit painstaking.