// 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>
#include <time.h>            // nanosleep

#define PROG_NAME	"lm75a"

// I2C Address
#define LM75A   0x48

#ifndef u8
typedef unsigned char u8;
#endif
#ifndef u16
typedef unsigned short u16;
#endif

// 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)

void msleep(int milliseconds)
{
	//usleep(milliseconds * 1000); // limited method
	struct timespec ts;
	ts.tv_sec = milliseconds / 1000;
	ts.tv_nsec = (milliseconds % 1000) * 1000000;
	nanosleep(&ts, NULL);
}

void printbinary16(u16 number)
{
  u16 mask = 0x8000; // most significant bit set
  while (mask) {
	printf("%c",mask & number?'1':'0');
	mask >>= 1;
  }
}

// Return number of i2c_msg's transferred, else negative value for error
int i2cWriteRead(int fd, int i2cAddress, u8 * pWriteData, int writeBytes, u8 * pReadData, int readBytes)
{
	struct i2c_msg msg[2];					// declare a two i2c_msg array
	struct i2c_rdwr_ioctl_data i2c_data;	// declare our i2c_rdwr_ioctl_data structure
	int msgsUsed=0;							// how many i2c_msg structures are used
	int result;								// return value from ioctl() call
	// Assume the first i2c_msg is used for writing
	if(pWriteData && writeBytes) {
		msg[0].addr = i2cAddress;
		msg[0].flags = 0;
		msg[0].buf = pWriteData;
		msg[0].len = writeBytes;
		msgsUsed++;

		// Load the second i2c_msg for receiving if the first one is used
		if(pReadData && readBytes) {
			// Load up receive msg
			msg[1].addr = i2cAddress;
			msg[1].flags = I2C_M_RD;
			msg[1].buf = pReadData;
			msg[1].len = readBytes;
			msgsUsed++;
		}
	}
	else if(pReadData && readBytes) {
		// Load the first i2c_msg for receiving (no transmit data)
		msg[0].addr = i2cAddress;
		msg[0].flags = I2C_M_RD;
		msg[0].buf = pReadData;
		msg[0].len = readBytes;
		msgsUsed++;
	}
	// Continue if we have data to transfer
	if(msgsUsed) {
		// i2c_msg array is loaded up.  Now load i2c_rdwr_ioctl_data structure.
		i2c_data.msgs = msg;
		i2c_data.nmsgs = msgsUsed;

		// With our open file descriptor, perform I2C message transfers
		// This function call returns the number of i2c_msg structures processed,
		// or a negative error value 
		result = ioctl(fd,I2C_RDWR,&i2c_data);
		if(result < 0)
		{
			printf("ioctl error: %s\n", strerror(errno));
			return -2;
	   }
	}
	else {
		printf("i2cWriteRead: No i2c_msg's processed\n");
	}
	
	return result; // return number of i2c_msg structures processed
}


int main(int argc, char * argv[])
{
	//printf("Content-type: text/html\n\n");
	// Open the i2c bus device where the chip resides
	int file = open("/dev/i2c-1",O_RDWR);
	if(file<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
	
	// Program the device to alert us when the temperature exceeds a threshold
	// If it gets to 30C (86F), signal using the OS pin (pull low)
	u8 tos[3] = {LM75A_REG_TOS,30,0};
	i2cWriteRead(file, LM75A, tos, sizeof(tos), NULL, 0);
	
	// Reset the OS pin (allow to go back high when temp goes down
	u8 thyst[3] = {LM75A_REG_THYST,29,0};
	i2cWriteRead(file, LM75A, thyst, sizeof(thyst), NULL, 0);

	while (1) {
		u8 index = LM75A_REG_TEMP; // Read temperature register
		u8 temperatureRegs[2]; // The MSB (first byte) is degree C units, the LSB is fractional component
		i2cWriteRead(file, LM75A, &index, 1, temperatureRegs, 2);
		
		// The following printf() is only accurate for positive temperatures..
		//printf("MSB: %d & %d/8ths C\n",temperatureRegs[0],temperatureRegs[1] >> 5); // shift fractional bits into position
        // This should be accurate for both positive and negative temperatures:
        u16 uTemp = (u16)temperatureRegs[0] << 8 | (u16)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;
		//printf("\033cTemp %0.1fF\n",fTempf);
		printbinary16(uTemp);
		printf("  0x%04X  %0.3fC  ",uTemp,fTemp);
		printf("%0.1fF\n",fTempf);
		sleep(1);
	}

	// clean up
	close(file);


	return 0;
}