I'm trying to use the i2c bus between Arduino nano 33 IOT and the Jetson Nano 2gb. I'm using the i2c bus and I want to send an array of integers to the Jetson Nano but when I receive data over the bus it's gibberish and destroys the data sent from the Jetson to the Arduino.

Jetson Nano pins: GND, 27 (SDA), 28 (SDL) Arduino Nano 33 IoT pins: GND, A4 (SDA), A5 (SCL)

Arduino code:

#include <Wire.h>

  int data [4];
  int x = 0;

  void setup() {                                 

  Serial.begin(9600);                        
  Wire.begin(0x6a);                          
  Wire.onReceive(receiveData);          
  Wire.onRequest(sendData);
  }

  void loop () {
      //sendData();
      delay(100);                         

  }

  void sendData() {
    int arr[4] = { 0, 23, 41, 19 };
    Serial.println("Sending Data to Jetson ...");
    //sendI2C((byte*) arr, sizeof(arr));
    Wire.write( (byte*)&arr, sizeof(arr));
    
    Serial.print("Sent...");
    Serial.println();
  }

  //void sendI2C(byte *data, int size) {
  //  Wire.beginTransmission(0x6a);
  //  for(int i = 0; i < size; i  ) {
  //    Wire.write(data[i]);
  //  }
  //  Wire.endTransmission();
  //}

  void receiveData(int byteCount) { 

     while(Wire.available() && x < 4) {               //Wire.available() returns the number of bytes available for retrieval with Wire.read(). Or it returns TRUE for values >0.
         data[x]=Wire.read();
         x  ;
       }

       if(x == 4) { x = 0; }

       Serial.println("----");
       Serial.print(data[0]);
       Serial.print("\t");
       Serial.print(data[1]);
       Serial.print("\t");
       Serial.print(data[2]);
       Serial.print("\t");
       Serial.println(data[3]);
       Serial.print("----");

       

       //sendData();

  }

Jetson Nano - Python3 code:

import smbus
  import time
  bus = smbus.SMBus(0)
  address = 0x6a

  def writeArray(a, b, c, d):
    bus.write_i2c_block_data(address, a, [b, c, d])
    return -1

  def readArray(bytes_nr):
    values = bus.read_i2c_block_data(address, 0x00, bytes_nr)
    return values


  while True:
    writeArray(14,42,95,0)
    time.sleep(1)
    values = readArray(8)
    print(values)

There are 2 things that happen:

1. When I only send data from the jetson nano to the arduino, on the Serial monitor of the arduino the data is received correctly: [14, 42, 95, 0]
2. When I try to sendData() to the Jetson Nano on the Jetson Nano console the data received 'print(values)' is like this:

[0, 0, 0, 0, 0, 0, 42, 105, 0 , 0, 4, 0 , 0 ,0 ,0 , 56, 0 , 0 , 0 ,0 ,0, 187, 0 , 0 ,0, 0, 0 , 0] 
  -- And on the Arduino console the data shifts from left to right so instead of receiving `[14, 42, 95, 0]`, It prints 

[8, 14, 42, 95] 

I'm just interested in sending an array of 4 integers from both sides.

Can someone extend a helping hand?

Thank you!

CodePudding user response：

Arduino code uses raw I2C protocol, Jetson uses SMBus on top of I2C. SMBus block structure implies 1 additional byte of length to be transferred.

CodePudding user response：

Thank you for the response @Dymyto Bagrii, I will read about the SMBus library and maybe come to a solution, I will post it if it works.

KR, Armand