NAME
        AllocSignal -- allocate a signal bit

   SYNOPSIS
        signalNum = AllocSignal(signalNum)
        D0                      D0

        byte allocsignal(byte);

   FUNCTION
        allocate a signal bit from the current tasks' pool.  either a
        particular bit, or the next free bit may be allocated.  The signal
        associated with the bit will be properly initialized (cleared).  At
        least 16 user signals are available per task.  Signals should be
        deallocated before the task exits.

        If the signal is already in use (or no free signals are available)
        a -1 is returned.

        Allocated signals are only valid for use with the task that
        allocated them.


   WARNING
        Signals may not be allocated or freed from exception handling code.

   INPUTS
        signalNum - the desired signal number {of 0..31} or -1 for no
                    preference.

   RESULTS
        signalNum - the signal bit number allocated {0..31}. If no signals
                    are available, this function returns -1.

   SEE ALSO
        freesignal()