Type ASSEMBLE
Source Lines : 1,803
Fixes Applied : 6
Most Recent Version : Tuesday, December 12, 1978
Last Fix ID : [R15315DS]

Module

       DMSXCP  ( EXCP ROUTINE )

Function

       PROVIDE THE FACILITY TO SIMULATE THE DOS/VS
       EXCP (SVC 0) UNDER THE CMS/DOS ENVIRONMENT.
       EXCP (EXECUTE CHANNEL PROGRAM) REQUESTS THE
       INITIATION OF AN I/O OPERATION TO A SPECIFIC
       LOGICAL UNIT.

Attributes

       CMSDOS SEGMENT RESIDENT MODULE
       REENTRANT

Operation

       1. SET UP NECESSARY ADDRESSABILITIES AND SAVE
          SOME REGISTERS IN THE EXCP WORK AREA. CHECK
          IF THE SPECIFIED CCW ADDRESS IN THE CCB IS
          NOT ZERO.

       2. DETERMINE IF THE SPECIFIED LOGICAL UNIT IN
          THE CCB IS ASSIGNED. IF IT IS ASSIGNED, USE
          THE PUB DEVICE TYPE TO INDEX AND BRANCH TO
          THE ONE INTERNAL ROUTINE THAT WILL PROCESS
          THAT SPECIFIC DEVICE. IF THE LOGICAL UNIT IS
          ASSIGNED TO IGNORE, ANOTHER ROUTINE IS GIVEN
          CONTROL.

       3. LOGICAL UNIT ASSIGNED TO 'IGNORE'.

          VERIFY THAT ALL THE CCW'S SPECIFIED ARE VALID.
          SEARCH THROUGH CCW CHAIN LOOKING FOR ANY READS.
          IF NO READ CCW IS FOUND, THE CCB IS POSTED WITH
          THE NORMAL C.E. + D.E. . IF A READ CCW IS FOUND,
          ASIDE FROM THE NORMAL C.E. + D.E., THE CCB IS
          POSTED FOR EOF.

       4. LOGICAL UNIT ASSIGNED TO 'PRINTER'.

          A 4 DOUBLE WORD WORK AREA IS ACQUIRED FROM FREE
          STORAGE TO BUILD THE DMSPIOSI PLIST. THE PLIST IS
          INITIALIZED WITH THE COMMAND NAME AND THE BUFDATA
          POINTER. THE FIRST USER CCW IS MOVED TO 'BUFDATA',
          AND A NO-OP CCW IS MOVED AFTER IT. IF THE CCW IS
          CHAINED, AN INTERNAL FLAG IS SET TO REMEBER THERE
          ARE MORE CCW'S TO EXECUTE. IF CCW IS NOT CHAINED,
          IT IS CHAINED TO THE NO-OP CCW. AN SVC 202 IS MADE
          TO DMSPIOSI TO EXECUTE THIS CCW. UPON RETURN, IF
          THERE ARE MORE CCWS, THE OPERATION IS REPEATED AS
          BEFORE. OTHERWISE, THE CCB IS POSTED ACCORDINGLY.

       5. LOGICAL UNIT ASSIGNED TO 'READER' OR 'PUNCH'.

          CHECK IF CCW CODE IS VALID. TURN STACKER SELECT
          AND DATA MODE BITS OFF (IF ON) AND PASS CCW CODE
          THROUGH TABLE OF SUPPORTED CCWS. ONCE A MATCH IS
          FOUND (WILL MATCH ON READ, WRITE, OR NO-OP), THE
          PLIST FOR DMSCIO IS BUILT, AND AN SVC 202 IS MADE
          TO CARDRD  OR  CARDPH (READ OR WRITE) TO PERFORM
          THE I/O OPERATION. UPON RETURN (OR IF THE CCW IS
          TO BE NO-OPED), IF THE CCW IS CHAINED, THE OPERA-
          TION IS REPEATED AS BEFORE. OTHERWISE, THE CCB IS
          POSTED ACCORDINGLY.

       6. LOGICAL UNIT ASSIGNED TO 'TERMINAL'.

          CHECK IF CCW CODE IS VALID BY PASSING CCW THROUGH
          A TABLE OF SUPPORTED CCWS. ONCE A MATCH IS FOUND
          (WILL MATCH ON READ, WRITE, OR NO-OP), THE PLIST
          FOR DMSCRD OR DMSCWR IS BUILT. IF READING, A 160
          BYTE BUFFER IS ACQUIRED FROM FREE STORAGE TO HOLD
          THE INPUT LINE. AN SVC 202 IS ISSUED TO CONREAD OR
          TYPLIN TO PERFORM THE I/O OPERATION. UPON RETURN,
          IF THE CCW IS CHAINED, THE OPERATION IS REPEATED
          AS BEFORE. OTHERWISE, THE CCB IS POSTED ACCORDINGLY.
          IF A READ WAS ISSUED, THE NUMBER OF BYTES SPECIFIED
          IN THE CCW ARE MOVED TO THE USER'S BUFFER. THEN THE
          ACQUIRED FREE STORAGE AREA IS FREED.

       7. LOGICAL UNIT ASSIGNED TO 'TAPE'.

          THE VIRTUAL DEVICE ADDRESS IS DECODED INTO A HEX
          ( EBCDIC ) REPRESENTATION FOR ANY POSSIBLE ERROR
          MESSAGE SUBSTITUTION.
          TWO DUMMY CCWS (MODESET AND TIC) ARE MOVED TO THE
          EXCP WORK AREA. A TEST IS MADE TO DETERMINE IF THE
          PUB CONTAINS A MODE SET VALUE. IF NOT, THE DEFAULT
          VALUE X'B3' IS USED. THE USER CCW CHAIN ADDRESS IS
          STORED INTO THE ADDRESS PORTION OF THE TIC CCW AND
          A CALL IS MADE TO DIAGNOSE THE CCW CHAIN TO CP.
          RETURN IS ONLY MADE IF AN I/O ERROR IS RETURNED BY
          CP (EXCLUDING UNIT EXCEPTION OR INCORRECT LENGTH).
          IF AN I/O ERROR OCCURED, THE SENSE BYTES ARE TESTED
          TO DIFFERENTIATE BETWEEN FILE PROTECTED TAPE OR I/O
          ERROR. OTHERWISE, THE CCW IS POSTED ACCORDINGLY.

       8. LOGICAL UNIT ASSIGNED TO 'DISK'.

          FIRST A CHECK IS MADE TO DETERMINE IF I/O IS TO CMS
          FORMATTED DISK, OR TO O/S OR DOS FORMATTED DISK. IF
          THE I/O IS TO A CMS FORMATTED DISK, THE CCW IS CHECKED
          FOR VALIDITY. IF THE CCW IS 'TIC', THE NEXT CCW IN THE
          CHAIN IS PROCESSED. IF THE CCW IS VALID AND NOT 'TIC',
          THE CCW IS PASSED THROUGH THE TABLE OF SUPPORTED CCW
          CODES. ONCE A MATCH IS FOUND, CONTROL WILL PASS TO THE
          ROUTINE TO PROCESS THAT CCW CODE. SUPPORTED CCW CODES
          UNDER CMS/DOS ARE: READ DATA, WRITE DATA, SEARCH ID,
          WRITE COUNT KEY & DATA, READ COUNT KEY & DATA, READ KEY
          AND DATA, AND READ COUNT. ALL OTHER VALID CCWS ARE NO-
          OPED. ONCE THE CCW HAS BEEN PROCESSED SUCCESSFULLY, A
          CHECK IS MADE TO DETERMINE IF THE CCW IS CHAINED. IF
          SO, THE NEXT CCW IS PROCESSED AS BEFORE, OTHERWISE, THE
          CCB IS POSTED ACCORDINGLY.

          IF THE DISK IS NOT A CMS FORMATTED DISK, A CHECK IS
          MADE TO DETERMINE IF THE DISK IS O/S OR DOS FORMATTED.
          THE CCW CHAIN IS THEN PASSED THROUGH A TEST TO FIND OUT
          IF THERE ARE ANY WRITE CCWS. IF A WRITE CCW IS FOUND,
          THE DISK IS CHECKED FOR WRITE MODE. IF THE DISK IS R/O
          THE CHANNEL PROGRAM IS NOT EXECUTED. NOW, THE CHANNEL
          PROGRAM IS DIAGNOSED TO CP FOR EXECUTION. UPON RETURN
          FROM THE CP DIAGNOSE, THE CCB IS POSTED ACCORDINGLY.

Calls to Other Routines

       DMSFRE, DMSPIO, DMSCIO, DMSCRD, DMSCWR
       DMSBRD, DMSBWR, DMSFNS, DMKGIO, DMSERR