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Debugging Techniques
Summary: In this section, you will learn about LabVIEW debugging techniques.
If a VI does not
run, it is a broken, or nonexecutable, VI. The
Run button often appears broken, shown at left,
when you create or edit a VI. If it is still broken when you
finish wiring the block diagram, the VI is broken and will not
run. Generally, this means that a required input is not wired,
or a wire is broken.
Finding Errors
Click the broken Run button or select
Windows>>Show Error List to display the
Error list window, which lists all the
errors. Double-click an error description to display the
relevant block diagram or front panel and highlight the
object that contains the error.
Execution Highlighting
View
an animation of the execution of the block diagram by
clicking the Highlight Execution button, shown
in Media 2. Execution highlighting shows the
flow of data on the block diagram from one node to another
using bubbles that move along the wires. Use execution
highlighting in conjunction with single-stepping to see how
data move from node to node through a VI.
note:
Execution highlighting greatly reduces the speed at which the VI runs.Single-Stepping
Single-step through a VI to view each action of the VI on
the block diagram as the VI runs. The single-stepping
buttons affect execution only in a VI or subVI in
single-step mode. Enter single-step mode by clicking the
Step Over or Step Into
button. Move the cursor over the Step Over,
Step Into, or Step Out button to
view a tip strip that describes the next step if you click
that button. You can single-step through subVIs or run them
normally.
If you
single-step through a VI with execution highlighting on, an
execution glyph, shown in Media 3, appears on
the icons of the subVIs that are currently running.
Probes
Use the
Probe tool, shown in Media 4, to
check intermediate values on a wire as a VFI runs. When
execution pauses at a node because of single-stepping or a
breakpoint, you also can probe the wire that just executed
to see the value that flowed through that wire.
You also can create a custom probe to specify which
indicator you use to view the probed data. For example, if
you are viewing numeric data, you can choose to see that
data in a chart within the probe. To create a custom probe,
right-click a wire and select Custom Probe>>New
from the shortcut menu.
Breakpoints
Use
the Breakpoint tool, shown in Media 5, to place a breakpoint on a VI, node, or wire
on the block diagram and pause execution at that
locatiFon. When you set a breakpoint on a wire, execution
pauses after data pass through the wire. Place a breakpoint
on the block diagram workspace to pause execution after all
nodes on the block diagram execute. When a VI pauses at a
breakpoint, LabVIEW brings the block diagram to the front
and uses a marquee to highlight the node or wire that
contains the breakpoint. LabVIEW highlights breakpoints with
red borders for nodes and block diagrams and red bullets for
wires. When you move the cursor over an existing breakpoint,
the black area of the Breakpoint tool cursor
appears white. Use the Breakpoint tool to click
an existing breakpoint to remove it.
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This work is licensed by National Instruments under a Creative Commons Attribution License (CC-BY 1.0), and is an Open Educational Resource.
Last edited by Elizabeth Gregory on Jul 16, 2004 2:54 pm GMT-5.
"A full introductory course on programming with LabVIEW."