// File: ds3231_3.cpp
// Read and display the current time - read from a DS3231 RTC on the I2C bus
// Author: Jim Merkle

#include <stdio.h>           // printf()
#include <sys/types.h>       // open()
#include <sys/stat.h>        // open()
#include <fcntl.h>           // open()
#include <sys/ioctl.h>       // ioctl()
#include <errno.h>           // errno
#include <string.h>          // strerror()
#include <unistd.h>          // close()
#include <linux/i2c-dev.h>   // struct i2c_msg
#include <linux/i2c.h>       // struct i2c_rdwr_ioctl_data

// The DS3231  is located on I2C bus 1, address 0x68
// The AT24C32 is located on I2C bus 1, address 0x56

#define I2C_DEVICE_NAME "/dev/i2c-1"
#define PROG_NAME	    "ds3231_2"
#define DS3231	        0x68
#define AT24C32	        0x56

#ifndef u8
typedef unsigned char u8;
#endif


// Return number of i2c_msg's transferred, else negative value for error
int i2cWriteRead(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;

		// Open file descriptor to I2C bus
		int fd = open(I2C_DEVICE_NAME,O_RDWR);
		if(fd<0) {
			printf("Failed to open i2c-1.");
			return -1;
		}
		// 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);
		close(fd); // go ahead and close open file descriptor		
		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
}

// Given a byte containing BCD format data, return unsigned char value
// Example: Convert 0x12 into the value 12 decimal : 0x0C
u8 bcdToInt(u8 bcd)
{
	u8 ret = bcd>>4;	// high nibble
	ret = (ret * 10) + (bcd & 0xF); // low nibble
	return ret;
}
	
// Given a byte of "normal" data, convert into BCD format data
// Example: Convert 0x20 (decimal 32) into 0x32
u8 intToBcd(u8 value)
{
	u8 ret = value / 10; // high nibble
	ret = (ret << 4) + (value % 10); // low nibble
	return ret;
}

// Given a month, 1-12, provide a month string
const char * monthString[] = {"zero","Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"};

int main(int argc, char * argv[])
{
	// Read the first 7 registers (index: 0-6) from the DS3231 into an array
    // The DS3231 will auto-increment the index register following each register read.
    // Thus, write the first index, then read all the registers you need
	unsigned char ucIndex = 0;
	unsigned char regData[7] = {0};
	int iResult = i2cWriteRead(DS3231, &ucIndex, sizeof(ucIndex), regData, sizeof(regData));
	if(iResult >= 0) {
		// array, regData, now contains the contents of the indexed registers 0 - 6 of the DS3231
        // The data is BCD, which displays wonderfully well when displayed as HEX (each nibble a digit)
        printf("%s %02X, %02X:%02X\n",monthString[bcdToInt(regData[5])], regData[4],regData[2],regData[1]);
	}
    else printf("Error calling i2cWriteRead()\n");
		
	return 0;
}