ViEnableEv​ent no longer works in 2.2 driver.

Question

I have an application, written in C++, that uses GPIB to talk to various kinds of instruments. Up until version 2.1 of the NI driver software, this application worked just fine. However, since version 2.2, whenever I try to execute this command:
Result = viEnableEvent (Session, VI_EVENT_SERVICE_REQ, VI_HNDLR | VI_QUEUE, VI_NULL);
...I get result -1073807196, which translates into:
"The specified mechanism is not supported for the given event type."
Is the mechanism I'm using obsolete? What should I be using in its place? Any pointers and tips gratefully accepted.
Regards,
Hans Guijt
TERMA B.V.
Schuttersveld 9
NL-2316 XG, Leiden
The Netherlands
Phone: [phone]
Telefax: [phone]
E-mail: [email protected]

Answer 1

Result = viEnableEvent (Session, VI_EVENT_SERVICE_REQ, VI_HNDLR | VI_QUEUE, VI_NULL);
I think your problem may be the VI_HNDLR | VI_QUEUE. These are exclusive. You either use a handler (callback function) or a queue (that you poll). Here is the online help summary:
"The viEnableEvent() operation enables notification of an event identified by the eventType parameter for mechanisms specified in the mechanism parameter. The specified session can be enabled to queue events by specifying VI_QUEUE. Applications can enable the session to invoke a callback function to execute the handler by specifying VI_HNDLR. The applications are required to install at least one handler to be enabled for this mode. Specifying VI_SUSPEND_HNDLR enables the session to receive callbacks, but the invocation of the handler is deferred to a later time. Successive calls to this operation replace the old callback mechanism with the new callback mechanism.
NI-VISA does not support enabling both the queue and the handler for the same event type on the same session. If you need to use both mechanisms for the same event type, you should open multiple sessions to the resource."