SEG39

Prolog  

Control Block Contents  
   SEG39 DSECT

Storage Layout  

Cross Reference (Contains links to field and bit definitions)  

SEG39 Prolog

 NAME       : HCPSEG39
 DESCRIPTION: ESA/390 - Segment Table Entry
 DSECT      : SEG39
 Function   : There is one segment table entry for each ESA/390
              megabyte of address space.  A segment table is
              made up of contiguous segment table entries.
              The format of the ESA/390 segment table entry is
              ARCHITECTED and cannot be changed in any way
              which violates the architecture.

SEG39 Control Block Content

SEG39 DSECT

Hex   Dec Type/Val   Lng Label (dup)    Comments
---- ---- --------- ---- -------------- --------
0000    0 Structure      SEG39          ESA/390 - Segment Table Entry
0000    0 Signed       4 SEGENTRY       Pointer to page table on 64 byte
                                        boundary.
          00000004       SEGLENTH       *-SEGENTRY Length of 1 segment
                                        table entry
0004    4 Signed       4 SEGNEXT (0)    Next segment table entry
0000    0 Bitstring    1 *              Bits 0-7 of page table origin.
                                        Bit 0 must be 0 in a valid STE.
0001    1 Bitstring    1 *              Bits 8-15 of page table origin
0002    2 Bitstring    1 *              Bits 16-23 of page table origin
0003    3 Bitstring    1 SEGSTAT        Segment table entry status. Left
                                        2 bits are bits 24-25 of PTO. (6
                                        bits appended on right form the
                                        page table origin.)
          ..1. ....      SEGINVAL       X'20' SEGINVAL Segment table
                                        entry is invalid
          ...1 ....      SEGCOMMN       X'10' SEGCOMMN Common segment bit
          .... 1111      SEGPTLNG       X'0F' SEGPTLNG Page table length
                                        (in units of 64 byte blocks,
                                        minus 1).
          0SEGSTAT       SEGPTOM        X'7FFFFFC0' SEGPTOM Isolate
                                        page-table origin
          ..1. ....      SEGINVM        X'00000020' SEGINVM Isolate
                                        invalid bit
          ...1 ....      SEGCOMM        X'00000010' SEGCOMM Isolate
                                        common-segment bit
          .... 1111      SEGPTLM        X'0000000F' SEGPTLM Isolate
                                        page-table length Notes : Since
                                        ESA/390 segment tables may be
                                        longer (up to 8K) than their
                                        boundary alignment (4K), a STO
                                        can not be computed from an STE
                                        address via a mask.
          ...1 .1..      SEGSHIFT       20 SEGSHIFT Bits to shift right
                                        to get segment number from an
                                        address or shift left to get
                                        starting segment address from a
                                        segment number
          .1.. ....      SEGPTUNT       64 SEGPTUNT Number of bytes in a
                                        "page-table unit", the number of
                                        bytes in the smallest variation
                                        of the size of a page table.
          .... .11.      SEGPTUNS       6 SEGPTUNS Number of bits to
                                        shift left in order to multiply
                                        by SEGPTUNT.
          ...1 ....      SEGPXPTL       12+4 SEGPXPTL Bits to shift right
                                        an isolated page index to obtain
                                        a page- table length.
          .... 1.1.      SEGPXDSP       12-2 SEGPXDSP Bits to shift right
                                        an isolated page index to obtain
                                        the displacement into the page
                                        table of the applicable PTE.

SEG39 Storage Layout

          
*** SEG39 - ESA/390 - Segment Table Entry
*
*     +---------------------------+
*   0 |         SEGENTRY          |
*     +---------------------------+
*
*** SEG39 - ESA/390 - Segment Table Entry
          
*** Overlay for SEGENTRY in SEG39
*
*     +------+------+------+------+
*   0 |//////|//////|//////|:STAT | 4
*     +------+------+------+------+
*
*** Overlay for SEGENTRY in SEG39

SEG39 Cross Reference

Symbol         Dspl Value
-------------- ---- -----
SEGCOMM        0003 10
SEGCOMMN       0003 10
SEGENTRY       0000
SEGINVAL       0003 20
SEGINVM        0003 20
SEGLENTH       0000 00000004
SEGNEXT        0004
SEGPTLM        0003 0F
SEGPTLNG       0003 0F
SEGPTOM        0003 0SEGSTAT
SEGPTUNS       0003 06
SEGPTUNT       0003 40
SEGPXDSP       0003 0A
SEGPXPTL       0003 10
SEGSHIFT       0003 14
SEGSTAT        0003