Pathway/iTS TCP and Terminal Programming Guide

TCP SETMODE Functions and CONTROL
Operations
Compaq NonStop™ Pathway/iTS TCP and Terminal Programming Guide—426751-001
9-6
Subsequent CONTROL 26 Calls
IOPROTOCOL = 1
IOPROTOCOL = 1 declares that the FEP does support CONTROL 26.
In this case, the TCP opens the FEP with a nowait depth of 2 and then issues the
CONTROL 26,1 call.
If the FEP responds with 70, the TCP subsequently uses CONTROL 26 calls to
terminate read requests prematurely.
If the FEP responds with any code other than 70, the TCP suspends the IDS requester
and records the event with an error code of 3054 in the PATHMON log file.
By specifying IOPROTOCOL = 1 when you are certain that CONTROL 26 will be
used, you eliminate some of the overhead inherent to the initialization sequence.
Overhead could be substantial if you are configuring and starting many requesters.
A requester written to handle CONTROL 26 does not operate properly if the FEP does
not support CONTROL 26.
Subsequent CONTROL 26 Calls
After the IDS requester and FEP have agreed to use CONTROL 26, the FEP should
always respond to any subsequent CONTROL 26 calls with a return code of 0.
The other supported return codes (187, 188, and 189) should be used only with the
underlying read operation—never with a CONTROL 26 call.
When the TCP issues a CONTROL 26 call, the FEP must, if it is able to do so, respond
in either of the following ways:
•
By completing the read with valid data and a return code of 0 and by completing the
CONTROL 26 call with a return code of 0
•
By completing the read with a return code of 187, 188, or 189 and by completing the
CONTROL 26 call with a return code of 0
Testing TERMINATION Codes
As a SCREEN COBOL programmer designing and coding an IDS requester, you do
nothing to initiate the use of CONTROL 26. The TCP determines whether to use
CONTROL 26, based on whether the external FEP supports the use of CONTROL 26
and on the SET TERM IOPROTOCOL specified at configuration.
What you must do, however, is test for certain TERMINATION-STATUS and
TERMINATION-SUBSTATUS codes in your ON ERROR and ESCAPE ON
UNSOLICITED MESSAGE paragraphs that can be generated by the use of
CONTROL 26.