HP 3000 Manuals HP 3000 Manuals
Comparing CONTROL-Y and Other Trap Handlers CONTROL-Y trap handlers differ from other trap handlers in that a process cannot arm a CM and an NM trap handler simultaneously. If the last call to XCONTRAP armed an NM trap handler, then the next CONTROL-Y trap invokes this procedure. If the program was running in CM at the time the CONTROL-Y trap occurred, the system actually switches to NM to enter the trap handler. The converse is also true. When called in NM, XCONTRAP can arm either a CM or an NM trap handler. The old plabel returned can be either CM or NM also. When called in CM, XCONTRAP can accept only CM plabels and returns only CM plabels. If XCONTRAP is called to configure a CM trap handler and the process' previous CONTROL-Y trap handler was an NM procedure, XCONTRAP returns 0 as the oldplabel value. This occurs because NM plabels are 32-bits, while a call to XCONTRAP in CM can return only a 16-bit plabel value.