Write the Hardware Specific C/C++ Code

Step 2 of 6 in Create a Digital Read Block

In most cases, to integrate device driver code into a Simulink^® block, you need to write a wrapper function around the API provided by the hardware vendor. Follow these steps to develop the C/C++ code required to implement digital read and write functionality:

1. Create a new empty file in the MATLAB^® Editor.

2. Copy the following C code into the file.

   #include <wiringPi.h>
   #include "digitalio_raspi.h" 
   static int initialized = false;
   
   void digitalIOSetup(uint8_T pin, boolean_T mode)
   { 
      // Perform one-time wiringPi initialization
      if (!initialized) { 
         wiringPiSetupGpio(); 
         initialized = 1;
      } 
   
   
      // mode = 0: Input 
      // mode = 1: Output
      if (mode) { 
         pinMode(pin, OUTPUT); 
      } 
      else 
      { 
         pinMode(pin, INPUT); 
      } 
   } 
   
   // Write a logic value to pin 
   void writeDigitalPin(uint8_T pin, boolean_T val) 
   { 
      digitalWrite(pin, val); 
   }
   
   // Read a logic value from pin 
   boolean_T readDigitalPin(uint8_T pin) 
   { 
      return ((boolean_T)digitalRead(pin)); 
   }

   This code wraps the Raspberry Pi^® C API to write to a digital I/O pin on the Raspberry Pi hardware board.

   Note

   Although the C code shown here is specific to the Raspberry Pi hardware, the same principle can be extended to any hardware-specific C/C++ API.

3. Save the file as digitalio_raspi.c into the source folder, src.

4. Create an empty header file and copy the following C++ code into the file.

   #ifndef _DIGITALIO_RASPI_H_
   #define _DIGITALIO_RASPI_H_
   #include "rtwtypes.h"
   
   void digitalIOSetup(uint8_T pin, boolean_T mode);
   void writeDigitalPin(uint8_T pin, boolean_T val);
   boolean_T readDigitalPin(uint8_T pin);
   
   #endif //_DIGITALIO_RASPI_H_

5. Save the file as digitalio_raspi.h into the include folder.

   This header file defines the C prototypes of the functions implemented in the C file, digitalio_raspi.c.

The digitalio_raspi.c function includes a wiringPi.h file that defines the pinMode and digitalRead functions. Simulink data types are used for pin and val variables. For this reason, the rtwtypes.h file is included in digitalio_raspi.h. You must include this file whenever you reference to Simulink data types. Because pin is a number between 0 and 53 we use the uint8_T data type to represent this variable.

In the next section, you will Select System Object Template and begin the populate the methods.