gtpc3m11 | Concepts and Structures |
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:
The control program routine specifies:
Notice that after the ECB is placed on the specified list, control is returned to the control program routine. The ECB must wait until it gets to the top of the specified list before it is activated.
Control is returned to the control program routine after the ECB is created. The control program routine can then perform additional processing (such as initializing work areas in the ECB) before the ECB is scheduled for processing. The control program routine is responsible for scheduling processing of the ECB by either placing it on a CPU loop list or by using an ENTNC macro request to activate it.
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.