NAME       : HCPIASIT
 DESCRIPTION: Internal-Address-Space-Identification
              Token
 DSECT      : IASIT
 FUNCTION   : This DSECT maps an i-ASIT, which is CP's internal
              identification of an address space.
 LOCATED BY : Any task needing an identification of an address
              space.  Some important fields which contain i-ASITs
              are:
              RSANASIT i-ASIT for "null" address space.
 CREATED BY : HCPSIT%I when translating various representations of
              address spaces into i-ASITs.
 DELETED BY : Any task which no longer needs the representation.
 RELOCATION CONSIDERATIONS : None
 NOTES      :
 An i-ASIT is an eight-byte token, doubleword aligned, and
 serves as a task's internal representation of a particular
 address space.  An i-ASIT contains information designating
 which address space, information defining the task's
 "capability" to access the address space, and information
 defining the method of translating addresses for that
 task.  Since it contains more information than just what
 is necessary to identify an address space, an i-ASIT
 cannot be directly compared to another i-ASIT to determine
 if the same space is designated.  A service routine (as
 provided by the HCPCMPIA macro) must be used for i-ASIT
 comparison purposes.
 The capabilities represented in an i-ASIT are the
 following:
   - r-access vs. i-access
   - Read/write vs. read/only permission
   - For guest instruction-stream references, whether
     guest prefixing, guest low-address protection,
     and guest fetch-protection override apply.
 Translation of a guest real address into a host real
 address is affected by whether or not the address space is
 the user's base address space, and whether or not the
 user's reference is a primary-space or secondary-space
 reference.  Prefixing, low-address protection, and
 fetch-protection override apply only when the space is the
 base, and when the access is a primary-space or
 secondary-space reference.
 An i-ASIT must be certified before it can be used for any
 purposes.  A certified i-ASIT is one that meets the
 following criteria:
    - The ASTE sequence number in the i-ASIT matches
      the ASTE sequence number in the ASTE (i- or r-access)
      *or*
    - ASCSEQNO <= ASITSN <= ASTSN          (r-access)
 The i-ASIT certification function is provided by either
 the HCPASMCI entry point or the HCPACERT macro (to be used
 only in cases where performance is a major concern, or the
 routine cannot call another routine which uses PFXTMPSV).
 Other services which process i-ASITS, such as HCPCMPIA
 and HCPCHCR7, handle certification of i-ASITs internally.

 IASIT DSECT
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Hex   Dec Type/Val   Lng Label (dup)    Comments
---- ---- --------- ---- -------------- --------
0000    0 Structure      IASIT          Internal-Address-Space-Identification
0000    0 Address      4 IASASTEO (0)   Bits 1-25 are the ASTE origin...
                                        host logical address. NOTE: This
                                        field may ONLY be used in a
                                        certified i-ASIT, otherwise, it
                                        may point to an ASTE which has no
                                        relation to the i-ASIT.
          00FFFFC0       IASASTOM       X'7FFFFFC0' Mask to apply to
                                        IASASTEO to isolate ASTE origin.
          .... ..1.      IASREADM       X'00000002' Mask for read-only
                                        bit
          .... ...1      IASFPRVM       X'00000001' Mask for
                                        force-private-space bit
0000    0 Bitstring    1 * (3)          First 3 bytes are ASTE origin
0003    3 Bitstring    1 IASFLAGS       Authorization/capability flags
          .... .1..      IASRACC        X'04' IASRACC When set, task has
                                        r-access to the address space.
          .... ..1.      IASREAD        X'02' IASREAD When set, task has
                                        read-only access to space.
          .... ...1      IASFPRIV       X'01' IASFPRIV
                                        Force-Private-Space bit When set,
                                        guest prefixing, low-address
                                        protection, and fetch-protection
                                        override do not apply. When not
                                        set, they do apply. Bits 0,
                                        26-28, and 32 are unused and will
                                        be zeros.
0004    4 Signed       4 IASASTSN       I-ASIT ASTE sequence number. It
                                        is compared with ASTE sequence
                                        number in ASTE.
          00000008       IASLEN         *-IASIT Length in bytes of an
                                        i-ASIT
          00000001       IASSIZE        (IASLEN+7)/8 Size in doublewords
                                        of an i-ASIT

          
*** IASIT - Internal-Address-Space-Identification
*
*     +--------------------+------+---------------------------+
*   0 |////////////////////|:FLAGS|         IASASTSN          |
*     +--------------------+------+---------------------------+
*   8
*
*** IASIT - Internal-Address-Space-Identification

 
Symbol         Dspl Value
-------------- ---- -----
IASASTEO       0000
IASASTOM       0000 00FFFFC0
IASASTSN       0004
IASFLAGS       0003
IASFPRIV       0003 01
IASFPRVM       0000 01
IASLEN         0004 00000008
IASRACC        0003 04
IASREAD        0003 02
IASREADM       0000 02
IASSIZE        0004 00000001