[Simh] pdp8i vs pdp8e

[Bob Supnik]

As the clock simulator says, it implements both the 8/E and 8/A 
instructions. It does not implement the 8/I.

The PDP-8 simulator is not an "all models" system; it only supports the 
8/E and 8/A.

Adding model-specific behavior (for the classic 8, 8/S, 8I/L, and 
distinguishing the 8/E from the 8/A) would not be impossible, but it 
would be fairly tedious and difficult to verify.  The earlier 8's use 
different peripherals for DECtape, magtape, line printer, and clock, 
among others, so new peripheral simulators would be needed, along with 
diagnostic and test programs.

/Bob

On 5/24/2010 12:00 PM, simh-request at trailing-edge.com wrote:
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> Today's Topics:
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>     1.  pdp-8 experts? (Brad Parker)
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> ----------------------------------------------------------------------
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> Message: 1
> Date: Sun, 23 May 2010 21:14:37 -0400
> From: Brad Parker<brad at heeltoe.com>
> Subject: [Simh] pdp-8 experts?
> To: simh at trailing-edge.com
> Message-ID:<4BF9D2FD.3060903 at heeltoe.com>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> 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
>
>
>
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