gtpc3m11Concepts and Structures

TPF System Control Transfer

The control program normally executes in supervisor state without an ECB. However, there are situations when the control program requires work to be performed in the ECB-controlled environment. An example is when OPZERO makes the transition from the control program environment to the ECB-controlled environment to start the processing of an input message.

The control transfer macro (CXFRC) is the facility that can be issued by any routine in the control program. This facility permits several modes of operation:

You may not be willing to review all of Step 4. Create an ECB and Select an Application. However, it is recommended that you review Step 4b. OPZERO Creates and Initializes an ECB because you are now in the position to understand how a newly created Entry is invoked by the OPZERO program. Remember that OPZERO is invoked by the CPU loop when it takes an item off the top of the input list on the main I-stream engine.