IBM OS/390 manual Interrupt Handling Routines, Interval Timer Interrupts

13.2.3 Interrupt Handling Routines

Interrupt routines take care of the interval timer, abnormal conditions, and operator communication interrupts. Abnormal condition interrupts will not be addressed in this publication.

13.2.3.1 Interval Timer Interrupts

Basically, the two ways of utilizing the interval timer in your programs are routine handling and wait handling.

Routine Handling

This method allows a branch to your own routine when the interval timer interrupt occurs. The following illustrates the VSE macros and corresponding MVS macro needed to perform this operation:

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿

￿	￿STXIT	￿IT, rou￿ine address ,		save area	￿
￿	￿	￿	(0)	(1)	￿
￿ VSE ￿SETIME		￿seconds			￿
￿	￿	￿	(1)		￿
￿	￿EXIT	￿IT			￿

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿

￿	￿	￿REAL	, ￿imer comple￿ion exi￿ address	￿
￿	￿	￿TASK	(2-12)	￿
￿	￿	￿WAIT		￿
￿	￿	￿	,DINTVL = address	￿
￿	￿	￿	(2-12)	￿
￿ MVS ￿STIMER		￿	,BINTVL = address	￿
￿	￿	￿	(2-12)	￿
￿	￿	￿	,TUNINTVL=address	￿
￿	￿	￿	(2-12)	￿
￿	￿	￿	,TOD = address	￿
￿	￿	￿	(2-12)	￿

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿

The VSE macro instructions allow you to execute a routine when a timer interrupt occurs and then to return to the program that was being executed prior to the interruption. The STXIT macro provides the address of the routine to be executed. A register save area must also be specified in the STXIT macro. The saving and restoring of the registers are performed automatically by the supervisor. The SETIME macro sets the interval timer. The EXIT macro returns from the specified routine (STXIT macro) to the point in the interrupted program where the interruption occurred.

The single MVS macro (STIMER) also allows you to execute a routine when the timer interrupt occurs. The REAL parameter indicates that time is to be decreased continually, while TASK means that the timer is stopped or adjusted only when the task is active. WAIT means that the job step is to be placed in a wait state until the interval expires. The timer completion exit address parameter is the same as the routine address used in the VSE STXIT macro.

The DINTVL parameter indicates that the time interval requested is in decimal units and is stored in the address specified. The MVS timer routine must follow the standard conventions for handling registers.

You must save the registers on initiation and restore them at routine termination.

Chapter 13. A s s e m b l e r 287