You can also feed a switch to nmi or interrupt and hook those to a debugger
in CP/M bios space.
Post by Nikolay DimitrovHi Ian,
Thanks for responding. Here's an explanation of why I was looking for this
info, hope it sheds some light.
My high-level idea was to explore to what extent the N8VEM machine is
possible to be "stand-alone" (or self-hosted if you want). My
interpretation for "stand-alone" is that the machine's software & hardware
should allow to rebuild its software & hardware (which if you think for a
while is non-trivial hard task), and also to be used for any simple
entertainment & work without a support from a PC host. For the SW part the
machine should be able to create new software, which in general means
editing, compiling and debugging code on the actual target (and this
environment should be friendlier than PDP-11/40 front panel). This is why I
was looking to find a Z80 capability similar to the 8088 trap flag, which
allows single-stepping through code, and thus the ability to have a
debugger running on the target itself. So far I haven't found any info
confirming that this is possible via the Z80 instruction set. For the HW
part, I was thinking that the machine should be able to run some form of
CAD SW (even a rudimentary one), that can be used to create schematics and
PCB. I think that at least theoretically this is possible, depending on
several important factors I was thinking to explore 1 by 1.
Ian, regarding the shared schematic - it looks like a manual single-step
mechanism, and it would be nice if there's a way to allow the SW running on
the Z80 to single-step a program (just like the old-school DOS DEBUG did
that). One possible solution could be to arm and trigger a pseudo-debug
interrupt after executing 1 instruction, so the debugger can get back the
control and examine the CPU state. I know that we can (brutally) extract
the Z80 state from an FPGA implementation, but I was also wondering how
this can be done on a off-the-shelf Z80.
As usual, feel free to share ideas (even crazy ones), and also to disagree
with me.
Kind regards,
Nikolay
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