Pathway/iTS TCP and Terminal Programming Guide

TCP SETMODE Functions and CONTROL
Operations
Compaq NonStop™ Pathway/iTS TCP and Terminal Programming Guide—426751-001
9-3
CONTROL Operations
CONTROL Operations
CONTROL is used to perform device-dependent I/O operations. When you design an
intelligent device support (IDS) requester to communicate with a front-end process
(FEP), you are concerned with the CONTROL operations described in Table 9-3
.
CONTROL 26 is discussed in detail later in this section.
Pathway/iTS and CONTROL 26
Compaq NonStop™ Pathway/iTS intelligent device support (IDS) SCREEN COBOL
requesters can interact with front-end processes outside of the PATHMON environment
that control intelligent devices such as automated teller machines, airline reservation
terminals, and personal computers. One type of front-end process, for example, could
be a SNAX/HLS application process.
The IDS requester sends messages to the FEP through SEND MESSAGE statements
and receives responses by the associated REPLY clauses.
As it interprets SEND MESSAGE statements and the associated REPLY clauses, the
TCP initiates the necessary write and read operations by issuing file system procedure
calls such as WRITE, READ, and WRITEREAD.
When a SEND MESSAGE statement includes a TIMEOUT or ESCAPE ON
UNSOLICITED MESSAGE clause, the TCP might have to terminate the underlying
read operation prematurely if either of those events occurs.
Ordinarily the TCP does this by issuing a CANCEL file system procedure call.
CANCEL calls are, however, ineffective for determining loss of data between the TCP
and the FEP. If the TCP uses a CANCEL call to terminate an outstanding read request,
the FEP cannot detect that the read no longer exists. When the FEP eventually responds
to the canceled read, it is likely that data will be lost and the integrity of the context for
subsequent operations compromised.
CONTROL 26 provides a better alternative.
Table 9-3. TCP CONTROL Operations
Operation Description Parameter
1 Control forms for conversational mode
(subtypes 0,2,3)
0 = form feed (send %014)
1-15 = vertical tab (send %013)
16-79 = skip param - 16 lines
11 Wait for modem connect none
12 Disconnect modem (hang up) none
22 Cancel an AM3270 I/0 operation none
26 Request immediate completion of all
outstanding I/O requests without loss of
data by the recipient of the CONTROL
26 request
none