Debugging a MATLAB Function Block

Debugging the Function in Simulation

In Create Custom Functionality Using MATLAB Function Block, you created an example model with a MATLAB Function block that calculates the mean and standard deviation for a set of input values. The software enables debugging for a MATLAB Function when you set a breakpoint.

To debug the MATLAB Function in this model:

Open the call_stats_block2 model and double-click the MATLAB Function block stats to open the editor.
In the MATLAB Function Block Editor, click the dash (-) in the left margin of the line:
```
len = length(vals);
```
A red dot appears in the line margin, indicating the breakpoint.
Simulate the model.
Simulation pauses when execution reaches the breakpoint. This is indicated by a green arrow in the margin.
In the toolbar, click Step to advance execution.
The execution arrow advances to the next line of stats, which calls the local function avg.
In the toolbar, click Step In.
Execution advances to enter the local function avg. Once you are in a local function, you can use the Step or Step In commands to advance execution. If the local function calls another local function, use Step In to enter it. If you want to execute the remaining lines of the local function, use Step Out.
Click Step to execute the only line in the local function avg. When the local function avg finishes executing, a green arrow, pointing down, appears under the last line of the function.
Click Step to return to the function stats.
Execution advances to the line after the call to the local function avg.
Click Step twice to calculate the stdev and to execute the plot function.
The plot function executes in MATLAB^®:
In the MATLAB Function Block Editor, a green arrow points down under the last line of code, indicating the completion of the function stats.
Click Continue to continue execution of the model.
The computed values of mean and stdev appear in the Display blocks.
In the MATLAB Function Block Editor, click Quit Debugging to stop simulation.

Set Conditions on Breakpoints

To help you debug code, you can enter a MATLAB expression as a condition on a breakpoint inside a MATLAB Function block. Simulation then pauses on that breakpoint only when the condition is true. To set a conditional breakpoint, in the MATLAB Function block editor, right-click beside the line of code and select Set Conditional Breakpoint. Type the condition in the pop-up window. You can use any valid MATLAB expression as a condition. This condition expression can include numerical values and any data that is in scope at the breakpoint.

To add or modify a condition on an existing breakpoint, right-click the breakpoint and select Set/Modify Condition. You can also perform these actions from the Breakpoints menu.

Watching Function Variables During Simulation

While you simulate a MATLAB Function block, you can use several tools to keep track of variable values in the function.

Watching with the Interactive Display

To display the value of a variable in the function of a MATLAB Function block during simulation:

In the MATLAB Function Block Editor, place the mouse cursor over the variable text and observe the pop-up display.
For example, to watch the variable len during simulation, place the mouse cursor over the text len in the code. The value of len appears adjacent to the cursor, as shown:

Watching with the Command Line Debugger

You can report the values for a function variable with the Command Line Debugger utility in the MATLAB window during simulation. When you reach a breakpoint, the Command Line Debugger prompt, debug>>, appears. At this prompt, you can see the value of a variable defined for the MATLAB Function block by entering its name:

debug>> stdev
 
	1.1180

debug>>

The Command Line Debugger also provides the following commands during simulation:

Command	Description
`ctrl-c`	Quit debugging and terminate simulation.
`dbcont`	Continue execution to next breakpoint.
`dbquit`	Quit debugging and terminate simulation.
`dbstep [in\|out]`	Advance to next program step after a breakpoint is encountered. Step over or step into/out of a MATLAB local function.
`help`	Display help for command line debugging.
`print <var>`	Display the value of the variable `var` in the current scope. If `var` is a vector or matrix, you can also index into `var`. For example, `var(1,2)`.
`save`	Saves all variables in the current scope to the specified file. Follows the syntax of the MATLAB `save` command. To retrieve variables to the MATLAB base workspace, use `load` command after simulation has been ended.
`<var>`	Equivalent to "print <var>" if variable is in the current scope.
`who`	Display the variables in the current scope.
`whos`	Display the size and class (type) of all variables in the current scope.

You can issue any other MATLAB command at the debug>> prompt, but the results are executed in the workspace of the MATLAB Function block. To issue a command in the MATLAB base workspace at the debug>> prompt, use the evalin command with the first argument 'base' followed by the second argument command, for example, evalin('base','whos'). To return to the MATLAB base workspace, use the dbquit command.

Watching with MATLAB

You can display the execution result of a MATLAB Function block line by omitting the terminating semicolon. If you do, execution results for the line are echoed to the MATLAB window during simulation.

Display Size Limits

The MATLAB Function Block Editor does not display the contents of matrices that have more than two dimensions or more than 200 elements. For matrices that exceed these limits, the MATLAB Function Block Editor displays the shape and base type only.

Checking for Data Range Violations

MATLAB Function blocks check inputs and outputs for data range violations when the input or output values enter or leave the blocks. To enable data range violation checking, set Simulation range checking in the Diagnostics: Data Validity pane of the Configuration Parameters dialog box to error.

Specifying a Range

To specify a range for input and output data, follow these steps:

In the Ports and Data Manager, select the input or output of interest.
The data properties dialog box opens.
In the data properties dialog box, select the General tab and enter a limit range, as described in Setting General Properties.

Debugging Tools

Use the following tools during a MATLAB Function block debugging session:

Tool Button	Description	Shortcut Key
Build	Access this tool from the Editor tab by selecting Build Model > Build. Check for errors and build a simulation application (if no errors are found) for the model containing this MATLAB Function block.	Ctrl+B
Update Diagram	Access this tool from the Editor tab by selecting Build Model > Update Diagram. Check for errors based on the latest changes you make to the MATLAB Function block.	Ctrl+D
Update Ports	Access this tool from the Editor tab by selecting Build Model > Update Ports. Updates the ports of the MATLAB Function block with the latest changes made to the function argument and return values without closing the MATLAB Function Block Editor.	Ctrl+Shift+A
Run Model	Start simulation of the model containing the MATLAB Function block. If execution is paused at a breakpoint, continues debugging.	F5
Stop Model	Stop simulation of the model containing the MATLAB Function block. Alternatively, from the Editor tab, select Quit Debugging if execution is paused at a breakpoint.	Shift+F5
Set/Clear	Access this tool by selecting Breakpoints > Set/Clear. Set a new breakpoint or clear an existing breakpoint for the selected line of code in the MATLAB Function block. The presence of the text cursor or highlighted text selects the line. A breakpoint indicator appears on the selected line. Alternatively, click the hyphen character (`-`) next to the line number. A breakpoint indicator appears in place of the hyphen. Click the breakpoint indicator to clear the breakpoint.	F12
Enable/Disable	Access this tool by selecting Breakpoints > Enable/Disable. Enable or disable an existing breakpoint for the selected line of code in the MATLAB Function block. If the breakpoint is disabled, an indicator appears on the selected line.	None
Set Condition	Access this tool by selecting Breakpoints > Set Condition. Set a condition on the breakpoint for the selected line of code in the MATLAB Function block. If the breakpoint has a condition associated with it, an indicator appears on the selected line.
Clear All	Access this tool by selecting Breakpoints > Clear All. Clear all existing breakpoints in the MATLAB Function block code.	None
Step	Step through the execution of the next line of code in the MATLAB Function block. This tool steps past function calls and does not enter called functions for line-by-line execution. You can use this tool only after execution has stopped at a breakpoint.	F10
Step In	Step through the execution of the next line of code in the MATLAB Function block. If the line calls a local function, step into the first line of the local function. You can use this tool only after execution has stopped at a breakpoint.	F11
Step Out	Step out of line-by-line execution of the current function or local function. If in a local function, the debugger continues to the line following the call to this local function. You can use this tool only after execution has stopped at a breakpoint.	Shift+F11
Continue	Continue debugging after a pause, such as stopping at a breakpoint. You can use this tool only after execution has stopped at a breakpoint.	F5
Quit Debugging	Exit debug mode. You can use this tool only after execution has stopped at a breakpoint.	Shift+F5

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