PDP-11/45 RSTS/E boot problem

Jon Elson elson at pico-systems.com
Mon Feb 4 20:59:52 CST 2019

On 02/04/2019 11:20 AM, Fritz Mueller via cctalk wrote:
> 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.
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.


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