Real-Time Workshop User's Guide

Device Driver Requirements and Limitations

In order to create a device driver block, the following components are required:

• Hardware-specific driver code, which handles communication between a real-time program and an I/O device. See your I/O device documentation for information on hardware requirements.
• S-function code, which implements the model initialization, output, and other functions required by the S-function API. The S-function code calls your driver code.

Your S-function code and the hardware-specific driver code are compiled and linked into a component that is bound to an S-Function block in your Simulink model. The MATLAB mex utility builds this component (a DLL under Windows, or a shared library under UNIX).

We recommend that you use the S-function template provided by the Real-Time Workshop as a starting point for developing your driver S-functions. The template file is

matlabroot/simulink/src/sfuntmpl.c 

An extensively commented version of the S-function template is also available. See matlabroot/simulink/src/sfuntmpl.doc.

The following components are optional:

• A TLC file that generates inline code for the S-function.
• A mask for the device driver block to create a customized user interface.

Limitations of Device Driver Blocks

The following limitations apply to noninlined driver blocks:

• Only a subset of MATLAB API functions are supported. See the "Noninlined S-functions" section of Chapter 4 of Writing S-Functions for a complete list of supported calls.
• Parameters must be doubles or characters contained in scalars, vectors, or 2-D matrices.

The following applies to inlined driver blocks:

• If the driver does not have a mdlRTW function, parameter restrictions are the same as for noninlined drivers.
• If the driver has a mdlRTW function, any parameter type is supported.

Preemption

Consider preemption issues in the design of your drivers. In a typical real-time program, a timer interrupt invokes rtOneStep, which in turn calls MdlOutputs, which in turn calls your input (ADC) and /or output (DAC) drivers. In this situation, your drivers are interruptible.

Inlined and Noninlined Drivers

Parameterizing Your Driver