NTS Exit Coding Requirements

Implementing the NTS User Exit › NTS Exit Coding Requirements

NTS Exit Coding Requirements

This section describes the coding requirements for the NTS exit.

Maintain Registers on Entry to an Exit

You must observe standard linkage conventions on entry to an exit.

On entry, the registers must be saved in the caller's save area, and on exit, restored (except R15, which contains a return code).

On entry, register contents are as follows:

R1	Contains address of a parameter list.
R2-R12	Unpredictable.
R13	Contains address of caller's standard save area.
R14	Caller's return address.
R15	Contains address of entry point of user exit.

Parameter List Format

The parameter list addressed by Register 1 on entry consists of one or two contiguous fullwords. If there are two fullwords, the first contains the address of another fullword that holds a function code indicating the reason that the exit is being called.

The second fullword of the parameter list is present for function codes 0 and 4 only. The high-order bit of this last (or solitary) fullword is not set; therefore, the length of the parameter list must be determined by examination of the function code as follows:

For function code 0, the second word of the parameter list contains the address of an area that contains system data that may be of value to the exit in determining its processing options.
For function code 4, the second word of the parameter list contains the address of the NTS session record being passed to the exit for examination.
For function code 8, the parameter list contains one word.

The following illustration shows the structure of the NTS user exit parameter list pointers.

This illustration shows the structure of the NEWS and NTS user exit parameter list pointers.