[Simh] The Missing PDP-8s

[Richard Cornwell]

Hi Bob,


> As was pointed out, the existing PDP-8 CPU is basically a PDP-8/E or 
> -8/A. It doesn't have the model-specific capabilities of the current 
> PDP-11 CPU simulator.
> 
> Making the PDP-8 "model specific" is a bit more difficult than just 
> putting in model tests at various points in the CPU. The peripherals, 
> and the peripheral instruction sets, evolved too. The PDP-8's DECtape 
> controller is quite different from the TC08; the magtape controller
> is different as well. With the 8/E, the original IOP 1,2,4 scheme was 
> replaced with the OmniBus, allowing peripherals to decode as many as
> 8 instructions per device code, instead of 3 or 4.
> 
> As for the PDP-5... it probably has different major peripherals too.
> So it's not just the PC = location 0 problem.
> 
> I looked at a PDP-12 implementation. It's not hard, but I really
> didn't want to do Yet Another DECtape Simulator for Linctape. With
> Rich Cornwell's recent work, it's clear that the DECtape controllers
> should have been abstracted to a library ten years ago, but doing so
> would be a major PITA, now that there are six (at least) distinct
> implementations (PDP1, PDP18b, PDP11, PDP8 TC, PDP8 TD, KA10).

   I am more then willing to switch to a generic library. What would be
   nice to see is something that just gave you the actual tape frames.
   This would also allow you to format the tape. If you write it I will
   gladly switch to it. Most of KA10 code is from your other simulators.

Rich

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Richard Cornwell
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