William "Chops" Westfield schreef op 05-Jan-15 om 10:36 AM:
> Multiple choice questions should not be answered from the=20
> point-of-view of a argumentative jerk. If you want to answer the=20
> capacitor question with "ripple current is the most important=20
> capacitor spec because I once designed a SMPS where that was so", then=20
> you should get the question wrong. IMO.=20

IMO a grading proces that dismisses that answer as wrong is itself wrong.

> My questions were aimed at the target audience mentioned in the=20
> original post.
>>> An interrupt request on a microprocessor is usually responded to
>>> a) within several instruction times
>>> b) within several microseconds
>>> c) within several milliseconds
>>> d) when the microprocessor is no longer busy
> Hmm.  I wanted (a), although I admit that I'd be happier if "microseconds=
" were longer compared to instruction cycles.  This was spurred by a discus=
sion on another forum along the lines of "are interrupts so slow that they'=
re making my clock inaccurate?"  I want people to realize that interrupts o=
ccur between instructions, and that instructions are now frequently signifi=
cantly shorter than a microsecond long.  (d) is meant to be VERY wrong - th=
e point of an interrupt is to go off and do something even though the proce=
ssor IS doing something else.  If you want to claim "I asumed by 'busy' you=
 meant 'in a critical section with interrupts disabled'"=85  See my comment=
 on argumentative.)  The big problem is that a lot of not-really-obsolete m=
icrocontrollers are pretty close to that "microsecond per instruction" timi=
ng (4MHz PICs and classic 8051s, to mention two.)
>
> I'm actually pretty happy that people are arguing over subtleties in my p=
roposed answers, rather than thinking that the questions are poor :-)

In most cases problem is not in the question but in the answers. "when=20
the microprocessor is no longer busy" - busy doing waht? executing an=20
instruction? or a micro-cycle? or a user-level application?

On most chips a) is definitely wrong: an interupt is handled after=20
*each* instruction. You can of course argue that "within several=20
instruction times" is included within "after each instruction", but I=20
would consider that argumentative.

Wouter

>
> BillW
>
>

--=20
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