ACC Programmer's Reference Guide

282 Chapter4
ZCOM C I/F Library Routines
ZSEND (3X)
If Bit ZCOM_ZSEND_NOMX (0x4000) of mode is set a nd the request is
to a outbound-multiplexed terminal ZLU, the outbound multiplexing is
over-ridden. This results in the data being sent directly to the terminal
(instead of the multiplexing program).
The ZCOM_ZSEND_MHD and ZCOM_ZSEND_NOMX bits are i ntended
for use by multiplexing programs to intercept terminal messages and
build specific messages or responses as required.
They can cause strange ZCOM subsystem behavior if used improperly;
hence, they must be used with caution.
If bit ZCOM_ZSEND_LPR (0x0080) or ZCOM_ZSEND_XPS (0x0040) is
set and the request is to a terminal, then the message will be queued on
the low priority or express transmit queue, respectively. Otherwise, it
defaults to the high priority queue.
The different transmit q ueues a llow the call er to have some control over
the order of messages being sent. The express queue is always processed
first and is not bounded by queue limit. It is i ntended for sending critical
control data and should never be used for normal data. The high priority
queue is subject toqueue limit checks and is intended for sending normal
data. The low priority queue is processed only after all express and high
priority messages are sent and is also bounded by queue limit checks. It
is intended for sending data in a background mode. For a busy terminal,
low priority messages will not be sent until all its higher priority
activities are completed.
Apart from the special bi ts, the mode value indicates the requested
completion status of the write:
* Mode=0 (ZcMODE_NO_WAIT - send no wait)
The message to be sent is moved to a buffer and the caller continues
executing without waiting for return status. If this mode is used, the
program is responsible for controlling the flow of messages. If the
calling program (or thread) uses too many buffers it will be
suspended until some of the buffers have been sent.
Even if the caller uses this mode and does not care about the return
status, it must still call zopen() to allocate a primary or auxiliary
input ZLU before making the zsend call.