Fixed-Point Blockset

Generating Pure Integer Code

All blocks generate pure integer code except for the FixPt Gateway In, FixPt Gateway In Inherited, and FixPt Gateway Out blocks. These blocks must generate floating-point code when handling floating-point input or output. However, if the input or output is an integer and the block is configured to treat the input or output as a stored integer, then these blocks will also generate pure integer code.

Example: Generating Pure Integer Code

This example outlines the steps you should take when generating pure integer code for your Fixed-Point Blockset model. The steps follow the description in the fxpdemo_code_only demo, which includes the model shown below.

Note    This example generates code using the Embedded C Real-Time Target (ERT), whch is available with the RTW Production Coder. If your version of the Real-Time Workshop does not support ERT code generation, then you may want to select the Generic Real-Time Target (GRT). Using GRT, all Fixed-Point Blockset blocks (except the gateway blocks) will generate pure integer code. However, the code related to the GRT infrastructure is not generated to exclude floating-point operations. For example, GRT may decide when to execute blocks based on a floating-point counter.

1. Copy the fixed-point portion of your model to a new model.

If your original model includes blocks that represent hardware, analog systems, and other blocks not related to embedded software, then you must create a new model. This new model contains only the fixed-point portion, which represents the software that will be running on the fixed-point processor. For example, the digital controller subsystem shown above contains the fixed-point blocks from the fxpdemo_feedback model used for code generation.

2. Insert FixPt Gateway In blocks, as needed.
   • Change the Treat input as: parameter from Real World Value to Stored Integer. This does not change the signal's value, but it is needed to "tag" integers with fixed point scaling information. The FixPt Gateway In block dialog box for this configuration is shown below.
   • Precede all FixPt Gateway In blocks with root level Inport blocks, and configure the blocks to use the appropriate integer data type. For example, the Inport block shown above is configured to use the built-in int8 data type.
3. Insert FixPt Gateway Out Blocks, as needed.
   • Change the Treat input as: parameter from Real World Value to Stored Integer. This does not change the signal's value, but it is needed to "strip" fixed-point scaling information from the integer. Also, configure the Output date type: parameter to use the appropriate integer data type. The FixPt Gateway Out block dialog box for this configuration is shown below.
   • Follow all FixPt Gateway Out blocks with root level Outport blocks.
4. Configure the simulation parameters.
   • Launch Simulink's Simulation Parameter's dialog box by selecting Parameters under the Simulation menu.
   • In the Solver window, configure Solver options: to Fixed-step and discrete (no continuous states), and configure Fixed step size: to the required value. The Solver window for this configuration is shown below.
   • Select the Real-Time Workshop window in the Simulation Parameters dialog box. Configure the System target file parameter to ert.tlc. The Template makefile and Make command parameters are automatically updated. This configuration is shown below.
     
     

   Launch the System Target File Browser by selecting the Browse button in the Configuration panel. If it is available, select Embedded-C Real-Time Target as the system target file and hit the OK button. The System Target File Browser for this configuration is shown below.
   
   

   The Fixed-Point Blockset supports all targets except those that generate Ada code. Note that you may not have ERT code generation capability. If this is the case, you should select the Generic Real-Time Target.

   • To configure the code generation parameters, select ERT code generation options from the Category parameter list. Select the Integer code only check box and any other options you may require. To configure additional code generation optimizations such as inlining, select General code generation options from the Category parameter list. The ERT code generation options for this configuration are shown below. If you are using GRT, the dialog box choices are slightly different.
     
     

   Note that all fixed-point blocks except gateway blocks produce pure integer code for all supported targets.

   • Build the code by selecting the Generate code button.

Code Generation Support

Using the Simulink Accelerator