C70:info-cpm (07/20/82)
>From rconn@BRL Tue Jul 20 12:35:15 1982
Good point ... I hadn't really used ZDT in moving thru a
ROM. If it uses the breakpoint-setting technique of instruction
execution, which would include setting one break point after a
jump and one at the jump address for a conditional branch unless
it was intelligent enough to examine the PSW flags to set only
one breakpoint, then it performs no simulation, but it still has
to perform some instruction interpretation.
Also, are you talking about ZDT or ZDDT? I haven't heard
of ZDDT.
Finally, the point of the message was to say that these
debuggers are definitely NOT emulators. I think the term "emula-
tor" is overworked and people have lost track of the meaning ...
emulation involves microcode which actually examines and executes
instructions for one processor on the architecture of another.
Refer to any good text in computer architecture to see my point.
For those not familiar with the concept of microcode, we are
talking about gate-level (for horizontal microcode) or function-
level (for vertical microcode) instructions which are executed
within a CPU to interpret and execute the machine language in-
structions. Several machines, such as the VAX 11/780 and PDP
11/60, are microprogrammable by the user (some "tricks" have to
be used by the VAX user to do this, tho), and the nature of the
machine-language instructions recognized and executed by the CPU
can be changed.
Rick