Program design architecture for sensors application in embedded device - c++

Question

I'm not an expert with C++ since I come from an electronics background.
I'm trying to make a Arduino program that allows anyone to add a sensors easily to a Arduino device using a standard format.
I thought of making a HAL for each sensor, for that I have created a class named Sensor which is the base class for each sensor. The user has to create a subclass that inherits from the Sensor class. This subclass for example is called Sensor_2 (2 is the ID) and it implements functions like:
uint16_t getID( void );
uint8_t getAvailableChannels( void );
void sampleChannel( uint8_t aChannel, uint8_t *aDataSize, uint8_t aDataBuffer[] );
This class is the one that calls its own sensor library which is dependent of the sensor.
Doing it this way I can sample every sensor in an standard way without having to rewrite each sensor library.
I don't know if that is the way to do it but I can't think of anything better.
I have tried to implement that with the following code:
Sensor.h
#ifndef SENSOR_H
#define SENSOR_H
#include "Arduino.h"
class Sensor
{
public:
Sensor();
virtual uint16_t getID( void );
virtual uint8_t getAvailableChannels( void );
virtual void sampleChannel( uint8_t channel, uint8_t dataSize, uint8_t dataBuffer[]);
};
#endif
Sensor_2.h
#ifndef Sensor_2_H
#define Sensor_2_H
#include "Arduino.h"
#include "../../Sensor.h"
#define ID 2
#define CHANNELS 1
class Sensor_2: public Sensor
{
public:
Sensor_2 ( void );
virtual uint16_t getID( void );
virtual uint8_t getAvailableChannels( void );
virtual void sampleChannel( uint8_t aChannel, uint8_t *aDataSize, uint8_t aDataBuffer[] );
};
#endif
Sensor_2.cpp
#include "Sensor_2.h"
Sensor_2::Sensor_2( void )
{
}
uint16_t Sensor_2::getID( void )
{
return (ID);
}
uint8_t Sensor_2::getAvailableChannels( void )
{
return (CHANNELS);
}
void sampleChannel( uint8_t aChannel, uint8_t *aDataSize, uint8_t aDataBuffer[] )
{
aDataSize = 1;
aDataBuffer[0] = hallRead();
}
main.cpp
#include <Logger.h>
#include "ComHandler.h"
#include "./Sensors/Sensor_2/Sensor_2.h"
ComHandler comHandler;
SensorManager* sensorManager = SensorManager::getInstance();
void setup()
{
Serial.begin(115200);
Logger::setLogLevel(Logger::WARNING);
Sensor_2 sensorHall = new Sensor_2;
sensorManager->addSensor(sensorHall);
}
void loop()
{
uint8_t* datasize;
uint16_t buffer[4];
comHandler.checkForData();
sensorManager.getAvailableSensors()[0].sampleChannel(0,dataSize, buffer);
}
The problem is that when trying to compile I get this error:
conversion from 'Sensor_2*' to non-scalar type 'Sensor_2' requested
Sensor_2 sensorHall = new Sensor_2;
^
If instead of:
Sensor_2 sensorHall = new Sensor_2;
I use:
Sensor_2 sensorHall;
I get:
sketch/Sensor.cpp.o:(.literal._ZN6SensorC2Ev+0x0): undefined reference to `vtable for Sensor'
sketch/Winja.ino.cpp.o:(.literal._Z5setupv+0x10): undefined reference to `Sensor_2::Sensor_2()'
sketch/Winja.ino.cpp.o: In function `setup()':
Do you think this is a good way to implement a solution to my problem? If so, how could I fix my error?

Answer 1

If I understood the problem, here you have two issues (one is blocking, the other not).
As for the simplest problem, Sensor_2 sensorHall = new Sensor_2; is not valid, since the new keyword generates a pointer to the object. You have two ways to generate an object and to pass it to the sensor manager (I assume the sensor manager accepts pointer to sensors):
// Solution 1
Sensor_2 *sensorHall = new Sensor_2;
sensorManager->addSensor(sensorHall);
// Solution 2
Sensor_2 sensorHall;
sensorManager->addSensor(&sensorHall);
Please note, however, that if you use solution 2 you must put the sensor definition outside the function. If, for instance, you write
void setup() {
Sensor_2 sensorHall;
sensorManager->addSensor(&sensorHall);
}
then the sensor object will be destroyed after you exit the setup. In order to avoid this, write
Sensor_2 sensorHall;
void setup() {
sensorManager->addSensor(&sensorHall);
}
As for the main problem, I think that arduino does not compile source files outside the main sketch folder (and it does not recursively, so subfolders are not scanned).
However, what you are trying to do is usually done by implementing libraries. You can find different libraries and resources to understand how a library work (for instance, there is a library tutorial on the arduino website). You will have to create a folder inside the library folder, then put inside the source files (in this case you can use subfolders); the compilation will be successful. This way you won't need to copy these files in future projects: they will already be there.
If you don't want to make them shared, and still want to put them in a separate folder, IIRC you can make a special folder called src and put the source files there (again, not in subfolders). The src folder gets merged with the sketch folder when compiling.
My suggestion: make it a library. Fully reusable, easy to maintain, even a bit of highlighting...