The TRAP instructions in the 68000 generate traps 32-47.  Because many
independent pieces of system code may desire to use these traps, the
alloctrap() and freetrap() functions are provided.  these work in a
fashion similar to that used by allocsignal() and freesignal(), mentioned
in the "exec signals" chapter.

Allocating a trap is simply a bookkeeping job within a task.  It does not
affect how the system calls the trap handler; it helps coordinate who owns
what traps.  Exec does nothing to determine whether or not a task is
prepared to handle a particular trap.  It simply calls your code. It is up
to your program to handle the trap.

To allocate any trap, you can use the following code:

    if (-1 == (trap = AllocTrap(-1)))
        printf("all trap instructions are in use\n");

Or you can select a specific trap using this code:

    if (-1 == (trap = AllocTrap(3)))
        printf("trap #3 is in use\n");

To free a trap, you use the freetrap() function passing it the trap number
to be freed.