NAME       : HCPBIOPG
 DESCRIPTION: DASD Block I/O Storage Management Block
 DSECT      : BIOPG aka BIOBG
 FUNCTION   : Contains header information and room to
              allocate I/O related control blocks for
              DIAGNOSE 18, A4, 250 and *BLOCKIO.
 LOCATED BY : BIOPGNXT and BIOPGPRV links the list together
              (caller must remember the start)
 CREATED BY : HCPDPSGP
 DELETED BY : HCPDPSRP, HCPDPSCU
 RELOCATION CONSIDERATIONS : None
 COMMENTS   : This block comes in two sizes: 2040 bytes and
              4088 bytes.  The size chosen is determined by
              the length of the request.
              The BIOPG consists of a header and available storage.
              Its used as a source for control blocks.  The HCPDPCUT
              macro will obtain storage from the BIOPG to create
              control blocks such as the IORBK and DVIOPs. This avoids
              the need to call HCPFREE for each needed control block.
              When the storage in one BIOPG is used up, another is
              obtained and linked to the previous using BIOPGNXT.

 BIOPG DSECT
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Hex   Dec Type/Val   Lng Label (dup)    Comments
---- ---- --------- ---- -------------- --------
0000    0 Structure      BIOPG          DASD Block I/O Storage Management Block
0000    0 Signed       4 BIOPGNXT       Pointer to the next BIOPG block
                                        (0 if no more)
0004    4 Signed       4 *              Reserved for IBM use
0008    8 Signed       4 BIOPGAV        Pointer to the next available
                                        storage location
000C   12 Signed       4 BIOPGEND       Address of BIOBGEND/BIOPEND
0010   16 Bitstring 2024 BIOPDATA       Size of data area
          000007F8       BIOPEND        * Byte following end of BIOPG
          000000FF       BIOPGDWS       (((*-BIOPG)+7)/8) Size in
                                        doublewords
      Redefine the data area for the larger sized block.
      This larger block has a separate entry in the CBITABLE
      and uses BIOBG as it's ID.
0010   16 Bitstring 4072 BIOBDATA       Size of data area
          00000FF8       BIOBGEND       * Byte following end of BIOBG
          000001FF       BIOBGDWS       (((*-BIOPG)+7)/8) Size in
                                        doublewords

          
*** BIOPG - DASD Block I/O Storage Management Block
*
*     +---------------------------+---------------------------+
*   0 |         BIOPGNXT          |///////////////////////////|
*     +---------------------------+---------------------------+
*   8 |         BIOPGAV           |         BIOPGEND          |
*     +---------------------------+---------------------------+
*  10 |                                                       |
*     =                       BIOPDATA                        =
*     |                                                       |
*     +-------------------------------------------------------+
* 7F8
*
*** BIOPG - DASD Block I/O Storage Management Block
          
*** Overlay for BIOPDATA in BIOPG
*
*     +-------------------------------------------------------+
*  10 |                                                       |
*     =                       BIOBDATA                        =
*     |                                                       |
*     +-------------------------------------------------------+
* FF8
*
*** Overlay for BIOPDATA in BIOPG

 
Symbol         Dspl Value
-------------- ---- -----
BIOBDATA       0010
BIOBGDWS       0010 000001FF
BIOBGEND       0010 00000FF8
BIOPDATA       0010
BIOPEND        0010 000007F8
BIOPGAV        0008
BIOPGDWS       0010 000000FF
BIOPGEND       000C
BIOPGNXT       0000