#include <stdint.h>

/* Atom types */
#define ATOM_INVALID_TYPE 	0x0000
#define ATOM_VENDOR_TYPE 0x0001
#define ATOM_GPIO_TYPE	0x0002
#define ATOM_DT_TYPE 		0x0003
#define ATOM_CUSTOM_TYPE		0x0004
#define ATOM_HINVALID_TYPE	0xffff

#define ATOM_VENDOR_NUM 0x0000
#define ATOM_GPIO_NUM 0x0001
#define ATOM_DT_NUM 0x0002

//minimal sizes of data structures
#define HEADER_SIZE 12
#define ATOM_SIZE 10
#define VENDOR_SIZE 22
#define GPIO_SIZE 30
#define CRC_SIZE 2

#define GPIO_MIN 2
#define GPIO_COUNT 28

#define FORMAT_VERSION 0x01

#define CRC16 0x8005

/* EEPROM header structure */
struct header_t {
	uint32_t signature;
	unsigned char ver;
	unsigned char res;
	uint16_t numatoms;
	uint32_t eeplen;
};

/* Atom structure */
struct atom_t {
	uint16_t type;
	uint16_t count;
	uint32_t dlen;
	char* data;
	uint16_t crc16;
};

/* Vendor info atom data */
struct vendor_info_d {
	uint32_t serial_1; //least significant
	uint32_t serial_2;
	uint32_t serial_3;
	uint32_t serial_4; //most significant
	uint16_t pid;
	uint16_t pver;
	unsigned char vslen;
	unsigned char pslen;
	char* vstr;
	char* pstr;
};

/* GPIO map atom data */
struct gpio_map_d {
	unsigned char flags;
	unsigned char power;
	unsigned char pins[GPIO_COUNT];
};


uint16_t getcrc(char* data, unsigned int size) {
	
	uint16_t out = 0;
    int bits_read = 0, bit_flag;
	
    /* Sanity check: */
    if((data == NULL) || size==0)
        return 0;

    while(size > 0)
    {
        bit_flag = out >> 15;

        /* Get next bit: */
        out <<= 1;
        out |= (*data >> bits_read) & 1; // item a) work from the least significant bits

        /* Increment bit counter: */
        bits_read++;
        if(bits_read > 7)
        {
			bits_read = 0;
            data++;
            size--;
        }

        /* Cycle check: */
        if(bit_flag)
            out ^= CRC16;

    }

    // item b) "push out" the last 16 bits
    int i;
    for (i = 0; i < 16; ++i) {
        bit_flag = out >> 15;
        out <<= 1;
        if(bit_flag)
            out ^= CRC16;
    }

    // item c) reverse the bits
    uint16_t crc = 0;
    i = 0x8000;
    int j = 0x0001;
    for (; i != 0; i >>=1, j <<= 1) {
        if (i & out) crc |= j;
    }
	
    return crc;
}