[Simh] pdp-8 experts?

[Brad Parker]

Any pdp-8 experts here?

I've been fighting a problem with tss/8 for a bit.  I've been working on 
getting it to build from sources.
When I build for the pdp-8/e it seems to work correctly using simh.  
When I build for the the pdp-8/i
I have problems.

My goal is a clean build from sources for the 8/i.  But the KW8/I clock 
emulation in simh is (to my mind)
suspect.

I'm happy to go dig in the docs and look at the schematics, but I 
thought I'd ask here also.  In the TSS/8
sources they do this for the 8/I:

  244             IFZERO CPU <
  245             /KW8I           REAL TIME CLOCK
  246
  247       6137  CECI=6137                       /CLEAR AND ENABLE 
CLOCK AND INTERRUPT
  248       6133  CSCF=6133                       /SKIP AND CLEAR FLAG 
IF FLAG

Naturally, for the 8/e they say:

  256             IFZERO CPU-2 <
  257             CECI=6131                       /CLOCK ENABLE
  258             CSCF=6133                       /SKIP AND CLEAR FLAG 
IF FLAG
 
When I build for the 8/I I don't get clock interrupts the way I expect.  
Looking at the clock code in
simh 6137 won't enable lock interrupts.  6133 will skip and clear.  When 
I build for the 8/e I got
clock interrrupts.

Ages ago I wrote KW8/I verilog code from the specs I could find and it 
does interpret 6137 as CECI
and does enable clock interrupts.

Anyone have an opinion?

it may be that competing clock hardware (i.e. 8/i, 8/e, 8/a) have 
different ideas about 6137...

-brad