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Write the Hardware Specific C/C++ Code

Step 2 of 7 in Create a Digital Write 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 digitalWrite 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. The val variable is the value to be written to the digital output pin and is represented by boolean_T data type.

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

See Also

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Create a Digital Write Block
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