Using Simulink

Displaying Information About the Simulation

The Simulink debugger provides a set of commands that allow you to display block states, block inputs and outputs, and other information while running a model.

Displaying Block I/O

The debugger allows you to display block I/O by selecting the appropriate buttons on the debugger toolbar

or by entering the appropriate debugger command.

Command	Displays a Block's I/O
probe	Immediately
disp	At every breakpoint
trace	Whenever the block executes

Displaying I/O of Selected Block

To display the I/O of a block, select the block and clickin GUI mode or enter the probe command in command-line mode.

Command	Description
probe	Enter or exit probe mode. In probe mode, the debugger displays the current inputs and outputs of any block that you select in the model's block diagram. Typing any command causes the debugger to exit probe mode.
probe gcb	Display I/O of selected block.
probe s:b	Print the I/O of the block specified by system number s and block number b.

The debugger prints the current inputs, outputs, and states of the selected block in the debugger output pane (GUI mode) or the MATLAB command window.

The probe command comes in handy when you need to examine the I/O of a block whose I/O is not otherwise displayed. For example, suppose you are using the step command to run a model block by block. Each time you step the model, the debugger displays the inputs and outputs of the current block. The probe command lets you examine the I/O of other blocks as well. Similarly, suppose you are using the next command to step through a model by time steps. The next command does not display block I/O. However, if you need to examine a block's I/O after entering a next command, you can do so using the probe command.

Displaying Block I/O Automatically at Breakpoints

The disp command causes the debugger to display a specified block's inputs and outputs whenever it halts the simulation. You can specify a block either by entering its block index or by selecting it in the block diagram and entering gcb as the disp command argument. You can remove any block from the debugger's list of display points, using the undisp command. For example, to remove block 0:0, either select the block in the model diagram and enter undisp gcb or simply enter undisp 0:0.

Note    Automatic display of block I/O at breakpoints is not available in the debugger's GUI mode.

The disp command is useful when you need to monitor the I/O of a specific block or set of blocks as you step through a simulation. Using the disp command, you can specify the blocks you want to monitor and the debugger will then redisplay the I/O of those blocks on every step. Note that the debugger always displays the I/O of the current block when you step through a model block by block, using the step command. So, you do not need to use the disp command if you are interested in watching only the I/O of the current block.

Watching Block I/O

To watch a block, select the block and click in the debugger toolbar or enter the trace command. In GUI mode, if a breakpoint exists on the block, you can set a watch on it as well by selecting the watch check box for the block in the Break/Display points pane. In command-line mode, you can also specify the block by specifying its block index in the trace command. You can remove a block from the debugger's list of trace points, using the untrace command.

The debugger displays a watched block's I/O whenever the block executes. Watching a block allows you obtain a complete record of the block's I/O without having to stop the simulation.

Setting Breakpoints at Time Steps

Displaying Algebraic Loop Information