Bob Ammerman wrote:

> Of course this doesn't support re-entrancy or recursion, and can get messy 
> if the same function is called from an interrupt and mainline code.

In the case of the Hi-Tech PICC/PICC-18, calling functions from an ISR and
from main code can get messy, but doesn't have to. By default it is not
allowed; the compiler creates a call tree for main and one for each
interrupt vector, and there are no common functions allowed in different
call trees.

One can mark a function to be allowed to be called by two or more call
trees (with "#pragma interrupt_level"). In this case it is the program's
responsibility to make sure that this function never gets called from one
call tree while it is already running in another; that is, the program
needs to control access to it. (This is because these compilers don't
support re-entrancy, as Bob said.) 

Commonly, the interrupt that calls it (or all interrupts) gets disabled
before entering the function in the main code. If nothing speaks against
it, this is a simple and clean method to use a function in more than one
call tree.

Gerhard
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