// File: lm75a.cpp
// Continously read the temperature from a lm75a and display it.
// Author: Jim Merkle, 03/30/2017

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <linux/i2c-dev.h>
#include <sys/ioctl.h>
#include <stdint.h>
#include <errno.h>
#include <linux/i2c.h>


#define PROG_NAME	"lm75a"

// I2C Address
#define LM75A   0x48

// LM75A Registers
#define LM75A_REG_TEMP    0
#define LM75A_REG_CONF    1
#define LM75A_REG_THYST   2
#define LM75A_REG_TOS     3
#define LM75A_REG_PROD_ID 7  /* only applicable for TI manufactured part */

// Power On Defaults:
// 0: Read only temperature - 2 bytes
// 1: 0x00 Configuration
// 2: 0x4B THYST - 75 degrees C - 2 bytes
// 3: 0x50 TOS - 80 degrees C - 2 bytes
// 7: 0xA1 (TI only)

int main(int argc, char * argv[])
{
	// Open the i2c bus device where the chip resides
	int fd = open("/dev/i2c-1",O_RDWR);
	if(fd<0) {
		printf("Failed to open the bus.");
		/* ERROR HANDLING; you can check errno to see what went wrong */
		exit(1);
	}
	
	// By default, the LM75A configuration register is 0x00

	// Continously display the temperature every second
	while (1) {
		uint8_t index = LM75A_REG_TEMP; // Read temperature register
		uint8_t temperatureRegs[2];     // The MSB (first byte) is degree C units, the LSB is fractional component
	    struct i2c_msg msg[2];	        // declare a two i2c_msg array
	    struct i2c_rdwr_ioctl_data i2c_data;
	    // Load up first message - writing index to device
	    msg[0].addr = LM75A;
		msg[0].flags = 0;
		msg[0].buf = &index;
		msg[0].len = 1;
		
		// Load up read message
		msg[1].addr = LM75A;
		msg[1].flags = I2C_M_RD;
		msg[1].buf = temperatureRegs;
		msg[1].len = 2;
		
		i2c_data.msgs = msg; // point to struct i2c_msg array
		i2c_data.nmsgs = 2;  // quantity of struct i2c_msg

		// This function call returns the number of i2c_msg structures processed,
		// or a negative error value 
		int result = ioctl(fd,I2C_RDWR,&i2c_data);
		if(result < 0)
		{
			printf("ioctl error: %s\n", strerror(errno));
			return -2;
	    }
		// Combine the two bytes into a 16-bit value
        uint16_t uTemp = (uint16_t)temperatureRegs[0] << 8 | (uint16_t)temperatureRegs[1]; // high byte followed by low byte
		
		float fTemp = (short)uTemp;
		fTemp /= 256; // The float will keep the remainder
		// Convert into Fahrenheit
		float fTempf = fTemp*9/5 + 32;

		// Display the two bytes of data, and floating point temperature in degrees C
		printf("0x%04X  %0.3fC  ",uTemp,fTemp);
		printf("%0.1fF\n",fTempf);  // Display temperature in degrees F
		sleep(1);
	}

	// clean up
	close(fd);


	return 0;
}