User`s guide

DC 900-1516D 55
Chapter
4
Application Interface
Programmers who prefer not to use the DLITE embedded interface (described in
Chapter 3) have the option of writing their VMS application to communicate with the
Protogate protocol software by sending and receiving formatted packets to the ICP2432
device. This is done by issuing VMS queued I/O (QIO) requests to the device driver
(
ZJDRIVER) supplied by Protogate. This chapter describes the use of the VMS system
services as they apply to the Protogate device driver.
4.1 Device Driver Interface
The Protogate VMS device driver provides the interface between one or more VMS
application programs and the protocol software on the ICP2432. The VMS program
builds formatted buffers in user space which consist of one or more headers and a data
area. The headers contain information such as command and response codes that both
the program and the protocol software use to determine the type and purpose of each
packet. The Protogate VMS device driver provides a logical path to move these buffers
between AXP and ICP physical memory. The VMS program must do all the interpreta-
tion of data within the buffer.
The flow of information between the AXP and ICP generally follows a com-
mand/response sequence. For each command sent by the VMS program to the ICP, the
program receives a response from the protocol software. There are, however, exceptions
to the command/response rule due to the asynchronous nature of communications. For
instance, once a link is started, data packets from the remote end of the communication
line can be received at any time. These packets are read by the VMS program through