

{  PURPOSE:
{    This procedure is called to check for ring alarms and initiate the processing of
{    premptive communications before returning to a procedure running in a higher ring.
{
{  NOTE:
{    The design of this procedure allows it to be called by both pmp$call_ring_crossing_proc
{    during normal task operation and by pmp$intra_ring_popper during task termination.  The
{    procedure is entered with traps enabled, but returns to its caller with traps disabled.
{    If abnormal status is returned by pmp$activate_ring_alarm, traps are enabled and the
{    procedure is exited through pmp$exit.
{
{              PMP$RING_CROSSING_PROCEDURE
{
