> On Aug 12, 2019, at 10:17 PM, Johnny Billquist <[email protected]> wrote:
>
> ...
> The PDP-12 poses a more interesting problem, as it is a dual CPU thingy with
> shared memory and two totally different instruction sets, but some
> interaction between them...
I've never programmed one but I have a handbook somewhere, so from that memory:
it's not a "dual CPU" in the usual sense of two separate engines running in
parallel, interconnected by memory or by I/O channels. Instead, it's more like
compatibility mode in early VAXen, where you can flip between two instruction
sets through a mode control. So the basic structure of a SIMH cpu simulation
is unaffected; what changes is that there are two sets of opcode interpreters.
The I/O devices are also different; LINCtape is physically very similar to
DECtape but the programming interface is rather different (significantly more
advanced -- if I remember right, it will search for the requested block for you
rather than putting that job in the driver software).
paul
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