IBM: MEXBK

Programming Interface Information: This information is NOT intended to be
used as Programming Interfaces of VM/ESA. It is to be used for diagnosis only.

MEXBK

Prolog

Control Block Contents

MEXBK DSECT

MEXENTRY DSECT

Storage Layout

Cross Reference (Contains links to field and bit definitions)

MEXBK Prolog

 NAME       : HCPMEXBK
 DESCRIPTION: MULTIPLE EXPOSURE BLOCK
 DSECT      : MEXBK
 FUNCTION   : CONTAINS THE NECESSARY INFORMATION TO FIND EACH EXPOSURE
              FOR MULTIPLE EXPOSURE DEVICES.
 LOCATED BY : RDEVEXPB FIELD OF RDEV  - POINTER TO MEXBK
 CREATED BY : HCPRDAAT - DURING ATTACH OF A MULTIPLE EXPOSURE DASD DEVICE
 DELETED BY : HCPRDADT - DURING DETACH OF A MULTIPLE EXPOSURE DASD DEVICE

MEXBK Control Block Content


MEXBK DSECT
Hex   Dec Type/Val   Lng Label (dup)    Comments
---- ---- --------- ---- -------------- --------
0000    0 Structure      MEXBK          MULTIPLE EXPOSURE BLOCK
0000    0 Bitstring    1 MEXCTEXP       Count of exposure blocks.
0001    1 Bitstring    1 *              Reserved for IBM use.
     This is information for multiple exposure blocks. This information
     indicates what exposure to use next for the reads or writes.
0002    2 Bitstring    6 MEXRDWRI (0)
0002    2 Bitstring    1 MEXFRDEX       First read exposure
0003    3 Bitstring    1 MEXLRDEX       Last read exposure
0004    4 Bitstring    1 MEXCREAD       Current available read exposure
     These are the write exposures.
0005    5 Bitstring    1 MEXFWREX       First available write exposures
0006    6 Bitstring    1 MEXLWREX       Last write exposure
0007    7 Bitstring    1 MEXCWRIT       Current available write exposure
0008    8 Address      4 MEX1STEX       Address of location of the first
                                        exposure block.
000C   12 Signed       4 *              Reserved for IBM use.
0010   16 Bitstring   16 MEXEXPBK (0)   Address of the first exposure
                                        block.
0010   16 Address      4 *              Place for exposure block address.
          00000004       MEXENTLN       *-MEXEXPBK Length of an entry.
0014   20 Address      4 MEXNXTEX (3)   Place for three exposure block
                                        addresses.
          00000004       MEXEXPEC       L'MEXEXPBK/MEXENTLN Count of
                                        entries in the exposure block
                                        field MEXEXPBK.
          00000020       MEXLEN         *-MEXBK
          00000004       MEXSIZE        (MEXLEN+7)/8 Number of
                                        doublewords.
     Use this to DSECT the read and write areas MEXFRDEX, MEXLRDEX, MEXCRDIT
     and MEXFWREX, MEXLWREX, MEXCWRIT.

MEXENTRY DSECT
Hex   Dec Type/Val   Lng Label (dup)    Comments
---- ---- --------- ---- -------------- --------
0000    0 Structure      MEXENTRY       MULTIPLE EXPOSURE BLOCK
0000    0 Bitstring    1 MEXFIRST       First available write exposures
0001    1 Bitstring    1 MEXLAST        Last write exposure
0002    2 Bitstring    1 MEXCURR        Current available write exposure

MEXBK Storage Layout

*** MEXBK - MULTIPLE EXPOSURE BLOCK
*
*     +------+------+------+------+------+------+------+------+
*   0 |:CTEXP|//////|:FRDEX|:LRDEX|:CREAD|:FWREX|:LWREX|:CWRIT|
*     +------+------+------+------+------+------+------+------+
*   8 |         MEX1STEX          |///////////////////////////|
*     +---------------------------+---------------------------+
*  10 |///////////////////////////|         MEXNXTEX          |
*     +---------------------------+                           |
*     |                                                       |
*     +-------------------------------------------------------+
*  20
*
*** MEXBK - MULTIPLE EXPOSURE BLOCK
*** MEXENTRY - MULTIPLE EXPOSURE BLOCK
*
*     +------+------+------+
*   0 |:FIRST|:LAST |:CURR | 3
*     +------+------+------+
*
*** MEXENTRY - MULTIPLE EXPOSURE BLOCK