More limitations: the PDP8 interrupts are laid out in a single 32b word.
There isn't room to have an additional 12*2 = 24 interrupts; the word is
almost full.
If anyone wants to try this, I suggest looking at the PDP15
implementation, which supports 16 (or more) lines. It already has the
mechanisms needed, including use of a subroutine to map the IOT to a
line number, multiplexing all of the separate interrupts onto a master
input and a master output interrupt, and the code for varying the number
of lines. The PDP8 core will still need an extension to the DIB
mechanism, perhaps an optional "callout" to a configuration routine that
would fill in IO dispatches as it saw fit, rather than algorithmically
based on the DIB itself; and the PDP8 would need a more flexible, table
lookup based mapping algorithm from device number to line number.
/Bob
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