XBI1 entry for extended buffer list AMU, SPAC or TSCB

Entry:: XBI1
VIT option:: XBUF
Event:: Extended buffer list AMU, SPAC, or TSCB
VIT processing module:: ISTITCXB
Control is returned to:: INTRACE invoker

This record is produced when an extended buffer list APPC message unit (AMU), ShortPAC (SPAC), or transmission subsystem control block (TSCB) is built by VTAM®.

The number of trace records required to represent a VTAM internal extended buffer list is variable-based on the number of entries in the structure.

The first record in a request is XBI1. This record is followed with as many XBI2 and XBI3 record pairs as is necessary to record the entire VTAM internal extended buffer list contents. The first XBI2 and XBI3 record pair contains information relating to the extended buffer list control entry. Subsequent XBI2 and XBI3 record pairs contain information relating to extended buffer list data entries. In addition, if the internal extended buffer list spans more than one AMU, SPAC, or TSCB, then a new XBI1 record is recorded at the point at which a new AMU, SPAC, or TSCB is used. In this case, the XBI1 record contains the previous AMU, SPAC, or TSCB address so that the relationship between this record and the previous set of records can be maintained.

There is no limit to the number of trace entries that can be produced. Although VTAM groups records together as a single entity in terms of recording in the trace recording media, there is a finite limit to how many records can be written externally or recorded internally at one time. Because of multiprocessing, other VIT records from unrelated operations can be interleaved in the trace output between the XBUF entries for a given operation. To provide correlation between groups of XBUF entries, the AMU, SPAC, or TSCB address is traced in each entry.

Byte (hex): Contents
00–03: Record ID: C"XBI1"
04: ID is the primary address space ID (ASID). This field is 0 if the ASID is greater than X'FF'.
05–07: 0
08–0B: TSCB, SPAC, or AMU address
0C–0F: Address of the previous TSCB, SPAC, or AMU address, or zeros if this is the first TSCB, SPAC, or AMU.
10–13: Return address
14–1B: 0
1C–1F: RPH address