Pathway/iTS TCP and Terminal Programming Guide

Designing Your Application
Compaq NonStop™ Pathway/iTS TCP and Terminal Programming Guide—426751-001
2-20
Requesters Using GDSX
For information about designing and coding requesters with the RSC/MP product, refer
to the Compaq NonStop™ Remote Server Call (RSC/MP) Programming Manual.
Requesters Using GDSX
The Extended General Device Support (GDSX) communications subsystem product
simplifies the development of front-end processes and back-end processes for
communication with I/O devices. These devices can be of any type, including
workstations, terminals, ATMs, point-of-sale (POS) devices, and industrial robots.
GDSX supplies code that provides multitasking and other features useful for developing
these front-end and back-end processes.
A GDSX process can act as a front-end process for LINKMON processes or a
Pathway/iTS terminal control process (TCP).
A GDSX process contains two primary parts:
•
TSCODE, supplied by Compaq
•
USCODE, supplied by the application programmer
TSCODE provides generic routines and management services that help you build a
multithreaded, fault-tolerant process. TSCODE provides the following functions:
•
Creates new tasks and stops tasks
•
Receives all system messages and I/O requests
•
Dispatches (wakes up and executes) the appropriate active task to process messages
and requests
•
Handles errors
USCODE consists of user exits that are called by TSCODE to handle the application-
specific, data communications-related functions, such as data manipulation, protocol
conversion, and message routing for the I/O process. USCODE is typically written in
the Transaction Application Language (TAL) and bound with TSCODE to produce a
functional GDSX process.
GDSX provides its own interface to Guardian procedures, NonStop™ TM/MP
procedures, and Pathsend procedures. The names of the GDSX procedures typically
look like their Guardian, NonStop™ TM/MP, or Pathsend equivalents, but they have a
circumflex (^) character inserted before the procedure name. For example,
BEGINTRANSACTION becomes ^BEGINTRANSACTION.
When a GDSX process is used as a front-end process, multiple threads of a user-coded
device handler provide separate tasks to manage the input from I/O devices and provide
functions such as data-stream conversion, implementation of a communications
protocol, and network communications error handling. One instance of the device
handler manages one I/O device.
In the Pathway environment, the GDSX process often simulates a terminal supported by
the TCP; the simulated terminal is typically run by an IDS requester program. When the
IDS facility is used, the GDSX product can be used to manage the line protocol
controlling the connected devices. The GDSX line handler (LH) task can be used to