TXXEXIT – Exit Routine

The Exit Routine terminates the top level RB and makes the next RB on the stack active.  If there are no more RB’s on the stack then the TCB is terminated.

000000                                9 TXXEXIT  CSECT ,
000000 18CF                          10          LR    R12,R15
                            00000    11          USING TXXEXIT,R12
                                     12 *
000002 8000 C0C8      000C8          13          SSM   =X'00'             DISABLE INTERRUPTS
                                     14 *
000006 5840 0010      00010          15          L     R4,16              CVT ADDRESS
00000A 5840 4000      00000          16          L     R4,CVTCTCB-@CVT(,R4)  GET TCB ADDRESS
00000E 5850 4008      00008          17          L     R5,TCBRB-@TCB(,R4)    GET RB  ADDRESS
                                     18 *
                            00000    19          USING @TCB,R4
                            00000    20          USING @RB,R5
                                     21 *
000012 1255                          22          LTR   R5,R5              ANY RB
000014 4780 C068      00068          23          BZ    XTCB                NO - TERMINATE TCB

Interrupts are disabled before any additional processing is done.  Since we will be modifying RB and TCB chains we don’t want the Dispatcher trying to dispatch a TCB we are modifying.  By disabling interrupts we know the Dispatcher will not gain control through an interrupt caused by the Interval Timer or and I/O interrupt.  We next get the current TCB address and the top level RB address.  If for some reason there is no RB we terminate the TCB.

000018 D23F 4020 5010 00020 00010    25          MVC   TCBREGS(64),RBREGS  COPY RB REGS TO TCB
00001E D207 4018 5008 00018 00008    26          MVC   TCBPSW(8),RBPSW     COPY RB PSW  TO TCB
000024 5810 5000      00000          27          L     R1,RBNEXT           NEXT RB ON CHAIN
000028 5010 4008      00008          28          ST    R1,TCBRB            UNCHAIN RB
                                     29 *
00002C 4110 0050      00050          30          LA    R1,RBLEN            LENGTH OF RB
000030 BF18 C0C9      000C9          31          ICM   R1,B'1000',=AL1(128)   SP=128
000034 1805                          32          LR    R0,R5                  RB ADDRESS TO FREE
                                     33          @CALL FREEMAIN               FREE STORAGE
000036 58F0 0014      00014          34+         L     R15,20             MVT ADDRESS
00003A 58F0 F01C      0001C          35+         L     R15,MVTFMAIN-@MVT(,R15) ROUTINE ADDRESS
00003E 05EF                          36+         BALR  R14,R15

We unchain the top level RB by taking the forward pointer in the RB and storing it in the TCB.  Now that the RB is off the chain we can free the storage associated with it.

000040 5850 4008      00008          38          L     R5,TCBRB            GET NEW CURRENT RB ADDRESS
000044 1255                          39          LTR   R5,R5               ANY RB
000046 4780 C068      00068          40          BZ    XTCB                NO - TERMINATE TCB
                                     41 *
00004A 9500 5004      00004          42          CLI   RBWTCNT,0           IS RB WAITING
00004E 4780 C05A      0005A          43          BE    EXIT010              NO - BRANCH
                                     44 *
000052 9680 4004      00004          45          OI    TCBFLGS,TCBFWAIT    SET WAIT BIT
000056 47F0 C05E      0005E          46          B     EXIT020
                                     48 *
00005A                               49 EXIT010  DS    0H
00005A 947F 4004      00004          50          NI    TCBFLGS,X'FF'-TCBFWAIT  CLEAR WAIT BIT
00005E                               51 EXIT020  DS    0H
00005E 58F0 0014      00014          52          L     R15,20              MVT ADDRESS
000062 58F0 F004      00004          53          L     R15,MVTDISP-@MVT(,R15)   DISPATCHER ENTRY
000066 07FF                          54          BR    R15                 GO TO DISPATCHER

Next we get the new top level RB address.  If we just removed the last RB for the TCB this pointer will be null and we need to terminate the TCB.  If there is a top level RB we propagate the wait status of the RB to the TCB.  If the RB wait count is not zero the TCB wait flag is set.  If the RB wait count is zero the TCB wait flag is cleared.  Control is then transferred to the Dispatcher to select the next task to dispatch.

000068                               57 XTCB     DS    0H
000068 5810 0010      00010          58          L     R1,16              CVT ADDRESS
00006C 5810 1004      00004          59          L     R1,CVTTASKQ-@CVT(,R1)   TOP OF TASK QUEUE
                                     60 *
000070                               61 XTCB010  DS    0H
000070 5820 1000      00000          62          L     R2,0(,R1)          POINT TO NEXT TCB
000074 1222                          63          LTR   R2,R2              END OF CHAIN ?
000076 4780 C0B8      000B8          64          BZ    XTCB900            SHOULD NOT HAPPEN - CAN'T FIND TCB
                                     65 *
00007A 1924                          66          CR    R2,R4              IS THIS OUR TCB
00007C 4780 C086      00086          67          BE    XTCB020              YES - BRANCH
                                     68 *
000080 1812                          69          LR    R1,R2              CHECK NEXT
000082 47F0 C070      00070          70          B     XTCB010                      TCB

This routine terminates the TCB when no RB’s are left.  First the the TCB chain is searched to locate the TCB that points to the TCB we are terminating.  We need this TCB address so we can unchain the terminating TCB.

000086                               73 XTCB020  DS    0H
000086 5830 2000      00000          74          L     R3,0(,R2)          UNCHAIN THIS
00008A 5030 1000      00000          75          ST    R3,0(,R1)                     TCB FROM QUEUE
                                     76 *
00008E 58B0 0010      00010          77          L     R11,16             CVT
000092 5810 B004      00004          78          L     R1,CVTTASKQ-@CVT(,R11)   TOP OF QUEUE (WAIT TASK)
000096 5010 B000      00000          79          ST    R1,CVTCTCB-@CVT(,R11)    MAKE CURRENT TASK
                                     80 *
00009A 4110 0060      00060          81          LA    R1,TCBLEN          LENGTH OF TCB
00009E BF18 C0C9      000C9          82          ICM   R1,B'1000',=AL1(128)   SP=128
0000A2 1804                          83          LR    R0,R4                  ADDRESS OF TCB TO FREE
                                     84          @CALL FREEMAIN
0000A4 58F0 0014      00014          85+         L     R15,20             MVT ADDRESS
0000A8 58F0 F01C      0001C          86+         L     R15,MVTFMAIN-@MVT(,R15) ROUTINE ADDRESS
0000AC 05EF                          87+         BALR  R14,R15
                                     88 *
0000AE 58F0 0014      00014          89          L     R15,20             MVT ADDRESS
0000B2 58F0 F004      00004          90          L     R15,MVTDISP-@MVT(,R15)   DISPATCHER
0000B6 07FF                          91          BR    R15

The TCB is removed from the chain and the Wait Task is made the current task.  This is necessary so the current task pointer will point to a valid TCB.  Now the TCB storage is freed and control is passed to the Dispatcher.

0000B8                               95 XTCB900  DS    0H
0000B8 8200 C0C0      000C0          96          LPSW  XTCBPSW
                                     97 *
0000C0                               98          DS    0D
0000C0 0002000000EE0005              99 XTCBPSW  DC    AL1(0,2,0,0),A(@E@EXIT)

If the terminating TCB is not found on the TCB chain an  unrecoverable error has occurred and a wait state PSW is loaded.

[Next – SVC 3 – Exit]

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