User`s guide

56 DC 900-1516D
ICP2432 User’s Guide for OpenVMS Alpha (DLITE Interface)
the QIO read path and are not associated with any command sent by the program.
Asynchronous line events such as sudden changes in modem control signals are
reported in the same way. For this reason, the VMS program should always keep a
no-wait read posted to each active link in order to handle any unexpected packets.
Protogate’s standard VMS device driver (
ZJDRIVER) provides an interface to the
ICP2432 that is used by several Protogate protocols. Although this driver follows the
general design of most other Digital device drivers, there are some functions that may
be different from other drivers. The following is a list of important facts about the stan-
dard Protogate driver:
• The driver assigns one device name (for example, ZJA0) for each ICP2432 board.
The user program accesses different ICP links through this one device name by
using node numbers (described later in this section). Multiple programs can
access the same device name.
• Except for download commands, all reads and writes are directed to a node num-
ber. Multiple programs can write to the same node number on the same ICP.
However, each program accessing the same ICP should read from a different node
number.
• Successful completion of a QIO write call simply means that the client buffer
(header and data) has been copied from AXP memory to ICP memory. The VMS
program must post a separate read to receive confirmation of the command or
data.
• If the VMS program is not able to post a QIO read for an incoming message
immediately, the message is not lost; if the ICP has available memory, it holds the
packet until the read is posted.
• VMS error codes found in the I/O Status Block (IOSB) of the QIO calls are differ-
ent from protocol error codes found in the protocol header.
• The Protogate driver does not support timer functions such as timed reads.