National Instruments NI VXIpc-882 Debugging

Chapter 4 Developing Your Application

triggers and interrupts, the controller parameter is ignored. If you need to

enable a remote controller for triggers, use the MAX frame resource to map

the trigger back to the local controller.

The interrupt and trigger routing in the NI-VXI 3.0 or later low-level

drivers is somewhat different from the default routing in previous versions

of NI-VXI. Therefore, the compatibility layer may behave differently than

the original NI-VXI API with regard to these settings. In particular, if you

are receiving triggers on an external controller, you may need to modify the

trigger configuration on your extender module using MAX. In general,

interrupts are routed automatically based on the interrupt configuration the

resource manager detects. Whether the changed routing behavior affects

your program is application dependent.

Because VISA is an instrument-centric API, certain functions from the

more controller-centric NI-VXI API do not match perfectly with a VISA

counterpart. When an application enables an event with the NI-VXI API

compatibility layer, each logical address is enabled for that event

separately. For example, if the application enables an interrupt level, VISA

will enable the interrupt on each logical address, one at a time, until all the

devices are enabled. This means that some interrupts could be lost from

devices with higher numbered logical addresses. MAX provides an

option for users to pick which logical address is enabled first. Select

Tools»NI-VXI»VXI Options. Set Prioritized Signal LA to the logical

address of the device that generates the events. This prevents possible loss

of events from that device.

Debugging

NI Spy and VISAIC are useful utilities for identifying the causes of

problems in your application.

NI Spy tracks the calls your application makes to National Instruments

programming interfaces, including NI-VISA, NI-VXI, and NI-488. NI Spy

highlights functions that return errors, so during development you can

quickly spot which functions failed during a program’s execution. NI Spy

can log the calls your program makes to these drivers so you can check

them for errors at your convenience, or use the NI Spy log as a reference

when discussing the problem with National Instruments technical support.

Figure 4-4 shows an example of a normal error returned from a call to

viMemAlloc when no memory has been shared.