Pathway/iTS TCP and Terminal Programming Guide

TCP SETMODE Functions and CONTROL
Operations
Compaq NonStop™ Pathway/iTS TCP and Terminal Programming Guide—426751-001
9-5
CONTROL 26 Initialization
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Complete the outstanding read by specifying that an associated input operation
within the FEP is still in progress and that the resultant data can be obtained by a
subsequent read operation (return code = 189)
The FEP must complete both the original read request and the CONTROL 26 call within
the allotted five minutes or the TERMINATION-STATUS register is set to 14 and
control passes to the SEND MESSAGE statement’s ON ERROR clause. If there is no
ON ERROR clause, the TCP suspends the requester and logs error 3174 to the devices
specified by the PATHCOM commands LOG1 and LOG2.
CONTROL 26 Initialization
As soon as the TCP opens the front-end process, the two processes engage in an
initialization sequence in which the TCP determines whether the FEP detects the use of
CONTROL 26.
That sequence is as follows:
1. The TCP issues a CONTROL 26,1 call.
2. The FEP sends back a reply code of 70 to indicate that it supports CONTROL 26.
Under normal circumstances, the TCP opens front-end processes with a nowait depth of
1 (allowing only a single I/O request to be outstanding at any given time).
To be able to use CONTROL 26 calls, however, the TCP must open the FEP with a
nowait depth of 2 (allowing both the original read request and a CONTROL 26 request
to be outstanding concurrently).
The IOPROTOCOL parameter of the PATHCOM SET TERM command allows you to
tell the TCP that the FEP supports the use of CONTROL 26. The TCP still performs the
initialization sequence but does it differently depending upon the value of
IOPROTOCOL.
IOPROTOCOL = 0
IOPROTOCOL = 0, which is the default value, declares that you do not know if the FEP
supports CONTROL 26.
In this case, the TCP opens the FEP with a nowait depth of 1 and then issues the
CONTROL 26,1 call.
If the FEP responds with 70, the TCP closes the file, reopens it with a nowait depth of 2,
and subsequently uses CONTROL 26 calls to terminate read requests prematurely.
If the FEP responds with any code other than 70, the TCP presumes that it does not
understand the use of CONTROL 26; the TCP subsequently uses CANCEL calls to
terminate read requests prematurely.