Passing HPDT receive requirements to VTAM

The XBUFLST-receive vector provides information to VTAM® about the area in which the application will receive CSM data. It is supplied to VTAM when the APPCCMD CONTROL=RECEIVE macroinstruction is issued with the VTROUTA=address and VTROUTL=length parameters specified. The XBUFLST-receive vector includes the following fields:

Storage Type (APC82SFL)

The application can indicate its preference for the type of CSM storage that should be used for inbound data. The application must specify at least one of these storage types.

APC82ECS X'80': Indicates that buffers in ECSA should be used for inbound data.
APC82CDS X'40': Indicates that buffers in a data space should be used for inbound data.

A mismatch between the storage type specified on the XBUFLST-receive vector and the storage type used for channel I/O (specified by the STORAGE parameter in the TRL major node) results in a data move. For best receive performance, the application should set both storage type flags on to indicate that either storage type is acceptable.

Buffer Length (APC82XBL)

This field specifies how much data VTAM should accumulate before completing a receive when the receive is operating in FILL=BUFF mode. When operating in FILL=LL mode, the buffer length parameter is ignored. The receive completion criteria uses this buffer length value the same as it would a real buffer length when in FILL=BUFF mode and XBUFLST is not specified.

When either QUALIFY=ANY or QUALIFY=IANY is specified, the FILL parameter is not specified. Data is received in the current mode of the receiving conversation, which is determined by either the CONMODE parameter of the previous APPCCMD macroinstruction processed or by the APPCCMD CONTROL=RESETRCV. If FILL=BUFF mode is in effect and if XBUFLST is specified, a buffer length value must be specified. For more information about conversations in FILL=BUFF mode, see Continuation modes for receiving normal information.

For more information about how to use the buffer length parameter, see Controlling the amount of data received.

Maximum Data (APC82MXD)

This is an optional field that specifies the maximum amount of data to be received. VTAM determines the amount of data to pass to the application based on one of the following settings, depending on the setting that is reached first:

One logical record, when FILL=LL
The size of the application's buffer area
The maximum data value

If maximum data is not specified, VTAM provides as much data as possible to the application.

This value must be specified as a fullword (maximum data value or binary 0's).

CSM Task Association TCB (APC82TSK)

This is an optional parameter that specifies the TCB to be used by VTAM for performing CSM task association for storage being passed to the application by way of the current APPCCMD. If this parameter is not specified, the storage is associated only with the application's address space. Applications executing in cross-memory mode should use this parameter to indicate the ACB task so that VTAM can associate the CSM buffers to the appropriate task.

This value must be specified as a fullword (TCB address or binary zeros).