Considerations for programs that invoke the TMP

The TMP must be given control by attaching it as a job step task in a state similar to that provided when JCL is used to cause the system to invoke it. Note that the TMP should be attached as the one and only JOBSTEP TCB.

APF-authorized
Primary addressing mode
AMODE(31)
Swappable
Key 8 PSW and application subpools

Registers:

Register	Contents
1	Address of primary mode parameter list, specifying the first command to be executed.
13	Address of a caller-provided key 8 save area.
14	Return address.
15	Address of entry point into the TMP.

See "Linkage Conventions" in z/OS MVS Programming: Assembler Services Guide for details.

Dynamic allocation can be used to satisfy the requirements for DD statements prior to passing control to the TMP.

Only one invocation of the TMP is supported during a step of a job, and only one instance of the TMP can be concurrently active within an address space.

Use of system services by the caller of the TMP during the TMP session can impact the timing and delivery of session services, and the TMP and the commands that it invokes can impact the timing and operation of the caller.

The TMP can alter execution status and the resources owned by the job during its operation. For example,

APF-authority can be relinquished.
Data set allocation can be changed.
Commands given control during the session can change any key 8 storage. ⋮

Some of these changes may remain in effect when control is returned to the caller of the TMP. When control is returned to the caller, all registers except for register 15 will contain the same values passed to the TMP on entry. Register 15 will contain a return code. See Figure 1 for more information about that return code.