interrupt service routine

interrupt service routine what are the rules of writing
the code for this ?

does the compiler HELP decribe this ?

In case I am writing c code for a specific embedded
system , how do i know how to write the code for
interrupt service routine ?

Yhanks
elico

Best source of info for writing any kernel code is:
http://lwn.net/Kernel/LDD3/

See chapter 10 for ISRs. The only special compiler setting is that you can't use any floating point registers in the kernel, since they aren't saved on system calls.

Many thanks
Elico