That last post was impressive, but I think it makes things way too
complicated.
Obviously something that does real-time operations should not be burdened
with a TSR. But it should also not be burdened with running DOS on legacy
hardware either. Nobody in their right mind is running something safety
critical on old PC hardware running DOS, so assume there is some room for
slop in the workload.
An SNMP agent TSR can do the following:
- Respond when polled; that's an important function right there.
("Heartbeat")
- "Guesstimate" the CPU utilization
- Pick up and report from whatever location in memory you care about.
The TSR has to respond to interrupts from the network device. It also
needs to hook the timer interrupt for ARP processing. Since you have the
timer interrupt hooked already, you can look at the stack to see the
interrupted address and estimate whether the interrupted code is in DOS, in
an idle loop in the main program, or whatever. (For a normal DOS system
that spends its time at the command prompt that is easy. For a
continuously running program that program must have an event handling loop,
and there are a few ways to detect and deal with that.)
Anyway, back to the question ... it's possible. If you are just going to
check a box for compliance reasons, then it's probably not doing unless the
cost of non-compliance is high. (If an ISO certification is riding on
this, spend the money to do something.) If this is really supposed to be
part of your monitoring solution and you need it, well, you've done well on
borrowed time ...
-Mike
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