/* 
	ADS1115_sample.c - 12/9/2013. Written by David Purdie as part of the openlabtools initiative
	Initiates and reads a single sample from the ADS1115 (without error handling)
*/

#include <stdio.h>
#include <fcntl.h>     // open
#include <inttypes.h>  // uint8_t, etc
#include <linux/i2c-dev.h> // I2C bus definitions

int main() {
	
  int ADS_address = 0x48;	// Address of our device on the I2C bus
  int I2CFile;
  
  uint8_t writeBuf[3];		// Buffer to store the 3 bytes that we write to the I2C device
  uint8_t readBuf[2];		// 2 byte buffer to store the data read from the I2C device
  
  int16_t val;				// Stores the 16 bit value of our ADC conversion
  
  I2CFile = open("/dev/i2c-1", O_RDWR);		// Open the I2C device
  
  ioctl(I2CFile, I2C_SLAVE, ADS_address);   // Specify the address of the I2C Slave to communicate with
	  
  // These three bytes are written to the ADS1115 to set the config register and start a conversion 
  writeBuf[0] = 1;			// This sets the pointer register so that the following two bytes write to the config register
  writeBuf[1] = 0xC3;   	// This sets the 8 MSBs of the config register (bits 15-8) to 11000011
  writeBuf[2] = 0x03;  		// This sets the 8 LSBs of the config register (bits 7-0) to 00000011
  
  // Initialize the buffer used to read data from the ADS1115 to 0
  readBuf[0]= 0;		
  readBuf[1]= 0;
	  
  // Write writeBuf to the ADS1115, the 3 specifies the number of bytes we are writing,
  // this begins a single conversion
  write(I2CFile, writeBuf, 3);	

  // Wait for the conversion to complete, this requires bit 15 to change from 0->1
  while ((readBuf[0] & 0x80) == 0)	// readBuf[0] contains 8 MSBs of config register, AND with 10000000 to select bit 15
  {
	  read(I2CFile, readBuf, 2);	// Read the config register into readBuf
  }

  writeBuf[0] = 0;					// Set pointer register to 0 to read from the conversion register
  write(I2CFile, writeBuf, 1);
  
  read(I2CFile, readBuf, 2);		// Read the contents of the conversion register into readBuf

  val = readBuf[0] << 8 | readBuf[1];	// Combine the two bytes of readBuf into a single 16 bit result 
  
  printf("Voltage Reading %f (V) \n", (float)val*4.096/32767.0);	// Print the result to terminal, first convert from binary value to mV
		
  close(I2CFile);
  
  return 0;

}