I2C with C#/Mono on linux

Question

I've got a small embedded device (Beaglebone Black) with a I2C device hooked up on /dev/i2c-2.

Now i'm trying to communicate with that device from C#/Mono, how is this possible? I've looked at some C++ code, but im not very strong in that language, but it looks like its possible just to open it as a file and write to it? Though im not sure how this code would translate to C#.

//C++ sample of i2c communication...
int BMA180Accelerometer::writeI2CDeviceByte(char address, char value){
    cout << "Starting BMA180 I2C sensor state write" << endl;
    char namebuf[MAX_BUS];
    snprintf(namebuf, sizeof(namebuf), "/dev/i2c-%d", I2CBus);
    int file;
    if ((file = open(namebuf, O_RDWR)) < 0){
        cout << "Failed to open BMA180 Sensor on " << namebuf << " I2C Bus" << endl;
        return(1);
    }
    if (ioctl(file, I2C_SLAVE, I2CAddress) < 0){
            cout << "I2C_SLAVE address " << I2CAddress << " failed..." << endl;
            return(2);
    }

    char buffer[2];
    buffer[0] = address;
        buffer[1] = value;
    if ( write(file, buffer, 2) != 2) {
        cout << "Failure to write values to I2C Device address." << endl;
        return(3);
    }
    close(file);
    cout << "Finished BMA180 I2C sensor state write" << endl;
    return 0;
}

Answer 1

I'm not sure if this is too late, but I have done this on a BBB using mono. You need to look at DLLImport attributes. Basically, you need to write a small C++ file and compile it that contains a custom method that just invokes ioctl() called invoke_ioctl(...) then place the compiled DLL into the /bin directory on your BBB and add this to your C# project code.

[DllImport("pinvoke.dll")]
[SuppressUnmanagedCodeSecurityAttribute()] //Optional, for speed
private static extern int invoke_ioctl(int file_handle, int address);

public static FileStream getI2CStream(byte address)
{
    FileStream result = File.Open("/dev/i2c-2", FileMode.Open);
    invoke_ioctl(result.SafeFileHandle.DangerousGetHandle().ToInt32(), address);
    return result;
}

This will setup ioctl() for the I2C line when writing to that specific I2C address. Just open files for each device on the I2C line. There is probably a C# way to do this too more safely/effectively.