Defpascal question

[CAMPER@AppleLink.Apple.COM (Camper, Dan)]

Question regarding the use of defpascal:
 
Are there any guidelines for what you can/cannot do within a defpascal function
or within a function directly called from there?  I'm thinking of potential
problems with moving memory, interrupting the current MCL process, etc..  I
don't want to go around rearranging vast amounts of memory without the
"correct" process knowing about it.
 
I know that some callbacks can occur during interrupt time, so that leads to
another question:  What is the proper way to write MCL code to handle those
callbacks?  Just queue up a handler form (via eval-enqueue) as fast as
possible?  Should I even attempt to handle those types of callbacks in Lisp?
 
Any ideas would be appreciated!
 
Dan