/* p9_3: I2C burst read from DS1337 */

/*
  This program communicates with the DS1337 Real-time Clock via I2C.
  The time, day (of the week), date, month and year are read using burst read. 
 
  DS1337 I2C parameters:
  fmax = 100 kHz, SCL PTE1, SDA PTE0 */

#include "MKL25Z4.h"
#include <stdio.h>
#include "UART.h"

#define SLAVE_ADDR 0x68     /* 1101 000. */
#define ERR_NONE 0
#define ERR_NO_ACK 0x01
#define ERR_ARB_LOST 0x02
#define ERR_BUS_BUSY 0x03

void I2C1_init(void);
int I2C1_burstRead(unsigned char slaveAddr, unsigned char memAddr, int byteCount, unsigned char* data, int* cnt);
void delayUs(int n);

int main(void)
{
    unsigned char timeDateReadback[7];
    int count;
    int rv;

    I2C1_init();

    rv = I2C1_burstRead(SLAVE_ADDR, 0, 7, timeDateReadback, &count);
    if (rv)
        for(;;) ;   /* replace with error handling */

    for (;;)
    {
    }
}

/* initialize I2C1 and the port pins */
void I2C1_init(void) {

    SIM->SCGC4 |= 0x80;         /* turn on clock to I2C1 */
    SIM->SCGC5 |= 0x2000;       /* turn on clock to PortE */
    PORTE->PCR[1] = 0x0600;     /* PTE1 I2C1 SCL */
    PORTE->PCR[0] = 0x0600;     /* PTE0 I2C1 SDA */

    I2C1->C1 = 0;               /* stop I2C1 */
    I2C1->S = 2;                /* Clear interrupt flag */
    I2C1->F = 0x1C;             /* set clock to 97.09KHz @13.981MHz bus clock */
    I2C1->C1 = 0x80;            /* enable I2C1 */
}

/* Use burst read to read multiple bytes from consecutive memory locations.
  Burst read: S-(saddr+w)-ACK-maddr-ACK-R-(saddr+r)-data-ACK-data-ACK-...-data-NACK-P
 */
int I2C1_burstRead(unsigned char slaveAddr, unsigned char memAddr, int byteCount, unsigned char* data, int* cnt) {
    int retry = 100;
    volatile unsigned char dummy;
    *cnt = 0;

    while (I2C1->S & 0x20) {    /* wait until bus is available */
        if (--retry <= 0)
            return ERR_BUS_BUSY;
        delayUs(100);
    }

    /* start */
    I2C1->C1 |= 0x10;           /* Tx on */
    I2C1->C1 |= 0x20;           /* become master */

    /* send slave address and write flag */
    I2C1->D = slaveAddr << 1;
    while(!(I2C1->S & 0x02));   /* wait for transfer complete */
    I2C1->S |= 0x02;            /* clear IF */
    if (I2C1->S & 0x10)         /* arbitration lost */
        return ERR_ARB_LOST;
    if (I2C1->S & 0x01)         /* got NACK from slave */
        return ERR_NO_ACK;

    /* send address of target register in slave */
    I2C1->D = memAddr;
    while(!(I2C1->S & 0x02));   /* wait for transfer complete */
    I2C1->S |= 0x02;            /* clear IF */
    if (I2C1->S & 0x01)         /* got NACK from slave */
        return ERR_NO_ACK;

    /* restart */
    I2C1->C1 |= 0x04;           /* send Restart */

    /* send slave address and read flag */
    I2C1->D = (slaveAddr << 1) | 1;
    while(!(I2C1->S & 0x02));   /* wait for transfer complete */
    I2C1->S |= 0x02;            /* clear IF */
    if (I2C1->S & 0x01)         /* got NACK from slave */
        return ERR_NO_ACK;

    /* change bus direction to read */
    I2C1->C1 &= ~0x18;          /* Tx off, prepare to give ACK */
    if (byteCount == 1)
        I2C1->C1 |= 0x08;       /* prepare to give NACK */
    dummy = I2C1->D;            /* dummy read to initiate bus read */

    /* read data */
    while (byteCount > 0) {
        if (byteCount == 1)
            I2C1->C1 |= 0x08;       /* prepare to give NACK for last byte */
        while(!(I2C1->S & 0x02));   /* wait for transfer complete */
        I2C1->S |= 0x02;            /* clear IF */
        if (byteCount == 1) {
            I2C1->C1 &= ~0x20;      /* stop the bus before reading last byte */
        }
        *data++ = I2C1->D;          /* read received data */
        byteCount--;
        (*cnt)++;
    }

    return ERR_NONE;
}

/* delay n microseconds */
/* The CPU core clock is set to MCGFLLCLK at 41.94 MHz in SystemInit(). */

void delayUs(int n)
{
    int i; int j;
    for(i = 0 ; i < n; i++) {
        for(j = 0; j < 7; j++) ;
    }
}