National Instruments NI-488.2 User Manual

Page 80

Chapter 8

NI-488.2 Programming Techniques

8-5

NI-488.2 User Manual

Both board-level and device-level

ibnotify

calls are supported by the

NI-488.2 driver. If you are using device-level calls, you can call

ibnotify

with a device handle for

and a

mask

of RQS, CMPL, END, or TIMO.

If you are using board-level calls, you can call

ibnotify

with a board

handle for

and a

mask

of any values except RQS. The

ibnotify

mask

bits are identical to the

ibwait

mask bits. In the example of waiting for

your GPIB device to request service, you might choose to pass

ibnotify

mask

with RQS (for device-level) or SRQI (for board-level).

The callback function that you register with the

ibnotify

call is invoked

by the NI-488.2 driver when one or more of the mask bits passed to

ibnotify

is TRUE.

The callback function is of type

GPIBNotifyCallback_t

and is defined

in the gpib header file,

ni4882.h

The callback function is passed a unit descriptor, the current values of the
NI-488.2 global variables, and the user-defined reference data that was
passed to the original

ibnotify

call. The NI-488.2 driver interprets the

return value for the callback as a mask value that is used to automatically
rearm the callback if it is non-zero. For a complete description of

ibnotify

, refer to the NI-488.2 Help. For instructions on accessing the

online help, refer to the

Using the NI-488.2 Documentation

section in

About This Manual

Note

The

ibnotify

callback is executed in a separate thread of execution from the rest

of your application. If your application will be performing other NI-488.2 operations while
it is using

ibnotify

, use the per-thread NI-488.2 globals that are provided by the

ThreadIbsta

ThreadIberr

, and

ThreadIbcnt

functions described in the

Writing

Multithreaded NI-488.2 Applications

section of this chapter. In addition, if your

application needs to share global variables with the callback, use a synchronization
primitive (for example, a semaphore) to protect access to any globals. For more
information about the use of synchronization primitives, refer to the documentation about
using operating system synchronization objects that came with your development tools.