Cannot send data via i2c to master raspberry pi

Projects Networking, Protocols, and Devices
10

It is working! I reviewed the code using in the correct way the "volatile" keyword and avoiding the use of serial object in the interrupt methods. So the final code if can be useful for others:

#include <Wire.h>

#define slaveAddress 0x08
#define INTERUPT_PIN 4

volatile  byte  command = 0;

volatile  byte  txTable[4];                               //for sending data over I2C
volatile  byte  rxTable[4];                               //for sending data over I2C
volatile  bool  newDataAvailable;

void setup()  
{
   Serial.begin(9600);
  
   Serial.println("Setup...");

   newDataAvailable = false;

   Wire.begin(slaveAddress);         //I2C slave address
  
  //Wire activates the internal pull-up resistors, let's deactivate them
  #ifndef cbi
    #define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
  #endif

  #if defined(__AVR_ATmega168__) || defined(__AVR_ATmega8__) || defined(__AVR_ATmega328P__)
    // deactivate internal pull-ups for twi
    // as per note from atmega8 manual pg167
    cbi(PORTC, 4);
    cbi(PORTC, 5);
  #else
    // deactivate internal pull-ups for twi
    // as per note from atmega128 manual pg204
    cbi(PORTD, 0);
    cbi(PORTD, 1);
  #endif  
  
  Wire.onReceive(i2cReceive);       //register handler onReceive
  Wire.onRequest(i2cTransmit);      //register handler onRequest

  Serial.println("...end.");
}//setup

void i2cReceive(int byteCount) {
  if (byteCount == 0) 
    return;
    
  // Commands in range 0x000-0x7F (0-127) are writes TO this slave, and expects nothing in return.
  // Commands in range 0x80-0xFF (128-255) are reads, requesting data FROM this device
  command = Wire.read();
  if (command < 0x80) {
     i2cHandleRx(command);
  }
}

void i2cTransmit() {
  //called by event
  byte numBytes = 0;

  switch (command) {
    case 0x90: 
      numBytes = 4;
      break;
  }
  
  if (numBytes = 4) {   
    Wire.write((byte*)txTable, numBytes);
  }
  
  //put down the interupt signal
  digitalWrite(INTERUPT_PIN, LOW);
}

byte i2cHandleRx(byte command) {
  // The I2C Master has sent data, store them in receiving buffer
  byte result = 0;
  
  switch (command) {
    case 0x0A:
      if (Wire.available() == 4)
      { 
        for (int i = 3; i >= 0; i--)
          rxTable[3-i] = Wire.read();
        
        result = 4;
      }
      break;     
  }
  if (result != 0)
    newDataAvailable = true; //let's say we have new data available and leave the receiving process

  return result;
}

In the code are missing some parts, like where I store or retrieve data from buffers or where I handle the start of transmission to the master.

Thank you very much for your help! :slight_smile: