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S:\agilent\8920\8920b\PRGGUIDE\BOOK\CHAPTERS\callproc.fb
Chapter 8, Programming the Call Processing Subsystem
Using the Call Processing Subsystem’s Remote User Interface
Advantages/Disadvantages of Polling
Polling has the advantage that the control program can react quicker to the change
in state since the control program does not have to execute the code necessary to
determine what condition caused the service request line to be asserted.
Polling has the disadvantage that, if improperly implemented, it can prevent the
Call Processing Subsystem from properly interfacing with the mobile station.
The Test Set has a multitasking architecture wherein multiple processes execute
on a priority driven and event driven basis. One of the highest priority processes is
the process that services the HP-IB.
If a control program constantly polls the status registers to determine when a
particular state is true, that state may take a very long time to go true or it may
never go to the true state. This is because the process which would cause that state
to go true will take a long time to complete or never complete because it is
constantly being interrupted by the HP-IB service process.
This condition may cause problems with the timing of the message protocol
between the Test Set and the mobile station. Therefore, care must be exercised
when using the polling technique to allow enough time between polls for
processes to execute within the Test Set.
Some computer systems and/or programming languages may not support the
service request feature of the HP-IB and consequently polling would be the only
technique available to the programmer. When using a polling technique be sure to
include a delay in the polling loop.
Advantages/Disadvantages of Using Service Request
The service request feature of the HP-IB has the advantage that it allows the Call
Processing Subsystem to execute at its maximum speed since processes within the
subsystem are not being constantly interrupted by the need to service the HP-IB.
The service request feature of the HP-IB has the disadvantage that it takes more
code to implement within the control program. The consequence of which is a
slight reduction in the overall throughput of the control program since more code
must be executed to accomplish the same task.
See “Setting Up and Enabling SRQ Interrupts” on page 294 for information on
using the service request method.
The choice of which technique to use, polling or service request, will depend upon
the needs of the particular application.