Design requirements

Follow these procedures when writing this routine:

Use standard linkage.
Save registers 0–14.

Consider the following restrictions when writing this routine:

The name of the session accounting exit routine module must be ISTAUCAG.
Note: The user must re-IPL when replacing or modifying his own accounting exit routine.
Do not issue any SVCs if this exit routine is running in SRB mode.
This exit routine should use only conditional storage invocations. You can reduce the possibility of a VTAM® abend during a storage shortage by coding conditional storage invocations.
All data is addressable in 24-bit mode only.
This exit routine must be link-edited into the appropriate library. See Installing VTAM exit routines for more information.
This exit routine operates as an internal VTAM subroutine. VTAM performance might be degraded if the routine requires lengthy processing time. While this routine has control, VTAM does not process any new operator requests, session initiation requests, or session termination requests for any resource.
System waits, including implied waits for I/O operations, should be avoided. System waits can cause VTAM failure in some timing-dependent situations.
This exit routine should not contain VTAM macroinstructions.
This exit routine operates enabled in pageable storage. Because the routine operates at VTAM's main task dispatching priority, there is a possibility of lockout if a wait requires another task action. The routine gets control in supervisor state with a VTAM storage key. Errors within the routine could damage VTAM or system control blocks and modules.
This exit routine provides the two LU names involved in the session. You can write this information to the System Management Facility (or an equivalent facility), along with the time of day. You can use these records to determine the session connection time. This exit does not have access to the logon data, VTAM control blocks, or TSO control blocks.
This exit routine is notified as part of an LU-LU session setup and takedown. You should design the routine to process requests involving only LU-LU sessions.
If an application program can establish parallel sessions, this exit routine must be capable of processing more than one request from the same LU-LU pair.