Updating and assembling the communications keypoint

The SNA table sizes and network characteristics are defined by the SNAKEY macro and assembled offline into the communications keypoint (CTK2).

This process eliminates the need to regenerate the z/TPF system when the network configuration changes, simplifying installation and tuning. The value of certain selected parameters in the communications keypoint can also be changed by using the ZNKEY command. For more information about the ZNKEY command, see z/TPF Operations.

The communications keypoint (CTK2) is a 4-KB record residing only in the basic subsystem (BSS). It is used to maintain the SNA network configuration and status. As a standard z/TPF keypoint, CTK2 has the following characteristics:
  • The address of the communications keypoint for each processor is contained in the image pointer keypoint (CTKX).
  • It is demand keypointed.
The communications keypoint is defined by the CK2SN DSECT and is divided into three major parts:
  • Part 1
    • Time stamp of the last build or modification.
    • SNA parameter list area. The contents of the SNA parameter list is defined in the SNAEQ macro and are initialized by SNA restart segments.
    • z/TPFAR storage allocation area table.
    • SNAKEY parameters.
    • Other system-wide communication configuration and status information.
  • Part 2
    • SNA main storage allocation tables (MSAT1 and MSAT2). MSAT1 and MSAT2 contain a parameter list for main storage SNA control block requirements.
      These tables allow the initializer, CTIN, to allocate main storage and fill in the dump label table without needing to know the main storage calculations for SNA support.
      Note:
      1. The subarea address table (SAT) is not user specified; it is always defined with 256 entries.
      2. The process selection vector (PSV) table area is not user specified; it is defined by using the values from the SNAEQ macro.
    • Other communication-related main storage allocation tables (MSAT3). MSAT3 contains a parameter list for main storage control block requirements that are not related to SNA communications. For example, MSAT3 contains a parameter list for the main storage Transmission Control Protocol/Internet Protocol (TCP/IP) support and z/TPF application requester (z/TPFAR) control block structures.

      MSAT3 allows the initializer, CTIN, to allocate main storage and fill in the dump label table without needing to know the main storage calculations for the communication-related tables.

    Each parameter list entry in the MSAT contains the following:
    • The 4-character dump label name of the control block; for example, CL4'SAT '.
    • The size of an entry in the control block.
    • The number of entries in the table to be allocated by CTIN.
    • A 4-byte field indicating the total main storage allocated for the control block.
    • A 4-byte field that is filled in by CTIN with the starting address of the allocated control block.
    • A table validity indicator to support fast recovery processing.
  • Part 3
    • The symbolic device address table (SDAT). The symbolic device address table is created by the system initialization process (SIP) with IODEV macros.

The communications keypoint is shipped as source code with default values supplied by the SNAKEY macro. The SIP process generates the JCL required to assemble the keypoint. Your system programmer must modify the SNAKEY macro before this assembly step to reflect your configuration. This keypoint can also be changed and reloaded at other times without rerunning the entire SIP process.

Your system programmer can change online the value of certain selected parameters in the communications keypoint with the ZNKEY command. Changes take effect either immediately, at cycle up, or after a restart depending on the parameters that were specified for the ZNKEY command.

Figure 1 shows how the required information is defined and passed through the various stages from SIP to the z/TPF online routines.
Figure 1. Communications keypoint generation
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