User`s guide

28 DC 900-1343D

DDCMP Programmer’s Guide

In the Freeway environment, the term blocking I/O indicates that the dlOpen, dlClose,

dlRead and dlWrite functions do not return until the I/O is complete. For non-blocking

I/O, these functions might return after the I/O has been queued at the client, but before

the transfer to Freeway is complete. The client must handle I/O completions at the soft-

ware interrupt level in the completion handler established by the

dlInit or dlOpen

function, or by periodic use of dlPoll to query the I/O completion status.

The

asyncIO DLI conﬁguration parameter speciﬁes whether an application session uses

blocking or non-blocking I/O. The

alwaysQIO DLI conﬁguration parameter further

qualiﬁes the operation of non-blocking I/O activity. Refer to the Freeway Data Link

Interface Reference Guide for more information.

The effects on different DLI functions, resulting from the choice of blocking or non-

blocking I/O, are explained in the Freeway Data Link Interface Reference Guide.

2.1.4 Buffer Management

Currently the interrelated Freeway, DLI, TSI and ICP buffers default to a size of 1024

bytes.

Caution

If you need to change a buffer size for your application, refer to the

Freeway Data Link Interface Reference Guide for explanations of

the complexities that you must consider.

2.2 Using the DLI in the Freeway DDCMP Environment

In the Freeway system, the client addresses Freeway sessions through the DLI. All DLI

requests in the DDCMP client application must use the DLI Raw operation, which is

discussed in detail in the Freeway Data Link Interface Reference Guide.