equivalent or better functionality. In 1975 typical
microprocessor needed external support chips, so there was
understandable resistance to putting something which was
not essential to running programs in processor chip.
But was this more of a philosophical thing? I think
even cheap CPUs in 1975 have flag registers, so
adding a TF to trigger int 1 seems like not a lot of
effort. Would it have increased the price of a CPU
by more than 0.1%?
And why does the 8086 have that when other processors
didn't for whatever reason?
And once we speak about external chips, folks who wanted
could add equivalent of debug registers using external
chips. Mass produces machines skipped debugging support
for cost reasons.
And this is the problem I would like to avoid. At least with
the benefit of hindsight, we know that programmers are
going to lose decent debug support if you don't put the
basic (breakpoints and TF) debug support into the CPU
BTW, I only learnt about this INT 1 and 3 mechanism
about a year ago.
I can't remember if I mentioned it, but PDOS/86 and
PDOS/386 (from pdos.org) now support a "monitor"
that uses those two facilities.