How to read data result from light sensor using interrupts

I'm using Arduino mega 2560 and light sensor BH1750FVI. to show result i'm using minicom, work on Ubuntu 16.04 LTS

I write code and it's work and send me data result reading from light sensor, i can read info only once. I don't understand how i make it work through interrupts (TWI_vect) and display the results every time using my uart.

#include "my_header.h"

#define I2C_STATUS_MASK                 0xF8
#define START_COND_TRANSMITTED          0x08
#define REPEATED_START_COND_TRANSMITTED 0x10
#define SLA_W_TRANSMITTED_ACK_RECEIVED  0x18
#define DATA_TRANSMITTED_ACK_RECEIVED   0x28
#define SLA_R_TRANSMITTED_ACK_RECEIVED  0x40
#define DATA_RECEIVED_ACK_RETURNED      0x50
#define DATA_RECEIVED_NACK_RETURNED     0x58
volatile int light_intensity = 0; // var for read data from sensor

ISR(USART0_UDRE_vect) {
  if (!bufferIsEmpty(&buffer)) //if we have something to read do it
    UDR0 = popFromBuff(&buffer);
  else
    UCSR0B &= ~_BV(UDRIE0); //disallow interrupts
}



int     main(void) {
  cli();
  init_port(); //initialize my port
  init_buffer(&buffer, BUFF_SIZE); //init ring_buffer for uart
  init_uart();
  TWI_init();
  sei();

  TWI_start(); //send start 
  TWI_send_SLA(WRITE); //send SLA+W to light sensor 
  TWI_sendData(0b00010000); //opecode for Measurement
  TWI_stop(); //stop

  TWI_start(); //send start 
  TWI_send_SLA(READ); // send SLA+R to sensor
  TWI_readData(); // read data from it light_intensity = TWDR
  TWI_stop(); // stop 
  u_printnumbers(light_intensity); /*my func that send data to ring_buffer and later
                      *using interrupts send it form buffer to UDR
                      */
  u_print("\n");

  while (1) {
    if (!bufferIsEmpty(&buffer)) /*if buffer is not empty allow interrupts for uart*/
      UCSR0B |= _BV(UDRIE0);
  }
}

So this code work and i receive data from sensor and all fine. But i want using it with interrupts (TWI_vect) and receive data all the time from sensor like in while(). i read a lot of info but don't understand how it should look. Can you show me the right way using my code with interrupts (TWI_vect) some little example. Thx for help!

Solution

To use the Two-Wirte interface (I²C; TWI) interrupt-driven, you will have to implement some sort of state machine inside the TWI ISR.

Atmel Application Note AVR135 give a slight idea how this can be done. You will have to have buffers ready and abstract transactions into a struct of some sort. For example, you can have a

struct i2c_transfer {
    uint8_t        i2c_sla; /* slave address */
    const uint8_t *txbuf;
    size_t         txbytes;
    uint8_t       *rxbuf;
    size_t         rxbytes;
}

That you set up, then have a function start transmitting I2C and check if you're done via checking if txbytes == 0 && rxbytes == 0 or an error occurred. Your ISR would then need to check its state and act appropriately depending on the number of bytes it's supposed to write and read.