Program Control And Special Instructions - HP 3000 III Series Manual

Machine Instructions and Stack Operations
4-13. Program Control and Special Instructions
DISP Dispatch
This instruction is used to transfer to the Dispatcher's entry
point: or to request such a transfer if executed while on the ICS
or within the range of a PSDB-PSEB pair.
Instruction Commentary 7.
Special opcode: 03, bits 12-15
=
0010
Indicators: See instruction commentary.
Traps: MODE, CSTV, TRACE, ABS CST, BNDV if user or privileged
This is a privileged instruction.
EXIT Exit From Procedure
~
, ,
N
This instruction is used to return from a procedure called by the
PCAL instruction or by some interrupts. A normal exit occurs by
restoring the return address to P, restoring the previous con-
tents of the Index and Status Registers, and deleting all stack
variables incurred by the called routine plus its marker, plus N
number of procedure parameters. The value of N may be any number
from 0 to 255 for exits from PCAL routines; it must be 0 for ex-
its from interrupt routines. If bit 0 of the return-P marker
word is a "1", control is transferred to Trace, segment #1, STT
#32 (decimal).
Instr uction Commentary 6.
SUb-opcode 3: 03
Indicators: Restored to values before PCAL
Traps: STUN (going to user mode),STOV, MODE, CSTV,TRACE, ABS CST,
BNDV if user or privileged
I XI T In te r r up t Ex i t
This instruction is used to exit from those interrupt service
routines which always run on the Interrupt Control Stack (ICS).
This results in a return to the interrupted process (which may be
another interrupt or the Dispatcher) or a transfer to the Dis-
patcher's entry point. The action taken depends in part on the
sequence of DISP, PSDB, and PSEB instructions which have been ex-
ecuted. IXIT is also used by the Dispatcher to exit to a process
being launched.
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