How can read more bytes via I2c

Question

I'm looking for an example on how to read more then 1 byte on Raspberry Pi via I2C. I see only this, but works only for the first byte sent:

package i2crpiarduino;

import com.pi4j.io.i2c.I2CBus;
import com.pi4j.io.i2c.I2CDevice;
import com.pi4j.io.i2c.I2CFactory;

import java.io.IOException;

import java.text.DecimalFormat;
import java.text.NumberFormat;


public class Arduino
{
  public final static int ARDUINO_ADDRESS = 0x04; // See RPi_I2C.ino
  private static boolean verbose = "true".equals(System.getProperty("arduino.verbose", "false"));

  private I2CBus bus;
  private I2CDevice arduino;

  public Arduino() throws I2CFactory.UnsupportedBusNumberException
  {
    this(ARDUINO_ADDRESS);
  }

  public Arduino(int address) throws I2CFactory.UnsupportedBusNumberException
  {
    try
    {
      // Get i2c bus
      bus = I2CFactory.getInstance(I2CBus.BUS_1); // Depends onthe RasPI version
      if (verbose)
        System.out.println("Connected to bus. OK.");

      // Get device itself
      arduino = bus.getDevice(address);
      if (verbose)
        System.out.println("Connected to device. OK.");
    }
    catch (IOException e)
    {
      System.err.println(e.getMessage());
    }
  }

  public void close()
  {
    try { this.bus.close(); }
    catch (IOException ioe) { ioe.printStackTrace(); }    
  }

  /*
   * methods readArduino, writeArduino
   * This where the communication protocol would be implemented.
   */
  public int readArduino()
    throws Exception
  {
    int r  = arduino.read();
    return r;
  }

  public void writeArduino(byte b)
    throws Exception
  {
    arduino.write(b);
  }

  private static void delay(float d) // d in seconds.
  {
    try { Thread.sleep((long)(d * 1000)); } catch (Exception ex) {}
  }

  public static void main(String[] args) throws I2CFactory.UnsupportedBusNumberException
  {
    final NumberFormat NF = new DecimalFormat("##00.00");
    Arduino sensor = new Arduino();
    int read = 0;

    while(true) 
   {
      try
      {
        read = sensor.readArduino();
      }
      catch (Exception ex)
      {
        System.err.println(ex.getMessage());
        ex.printStackTrace();
      }

      System.out.println("Read: " + NF.format(read));
      delay(1);
    }

  }
}

Objective:
I send via I2C a long number from my Arduino board to Raspberry Pi, but I'am trying without success to make this example work. How I can get the long number read from Raspberry Pi?

in the javadoc i see this:

public int read(byte[] buffer, int offset, int size) throws IOException
This method reads bytes directly from the i2c device to given buffer at asked offset.
Parameters:
buffer - buffer of data to be read from the i2c device in one go offset - offset in buffer size - number of bytes to be read 
Returns:
number of bytes read 
Throws:
IOException - thrown in case byte cannot be read from the i2c device or i2c bus

how I can use it?

score 0 · Answer 1 · answered Mar 12 '19 at 14:59

I2C works off of a "slave" system, where you have to send bytes out acknowledging the connected device you want data from, and the device responds accordingly. The read method being used does not send out flag bytes, and thus never gets data back; I2C is an on-demand method of communication.

Overview of I2C here: I2C bus protocol Tutorial, Interface with applications

How can read more bytes via I2c

1 Answers1