/*
 * This program writes and reads an I2C device on the Wytec EduBase board.
 *
 * The Wytec EduBase board has a real-time clock device (BQ32000) with I2C
 * interface.  This program writes a zero to the second register (address 0)
 * of the RTC and reads it back repetitively and display the second count
 * at the LEDs.  Since the second register uses binary coded decimal format,
 * the LEDs will count up from 0 to 9 in binary and wrap around to 0. 
 */

#include "MKL25Z4.h"

void I2C1_init(void);
int I2C1_byteRead(unsigned char slaveAddr, unsigned char memAddr, unsigned char* data);
int I2C1_byteWrite(unsigned char slaveAddr, unsigned char memAddr, unsigned char data);
void delayUs(int n);


#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

int main(void)
{
    unsigned char second;
    int rv;

    I2C1_init();
    
    /* enable PTC 6-3 as output for LEDs*/
    SIM->SCGC5 |= 0x800;        /* enable clock to Port C */
    PORTC->PCR[3] = 0x100;      /* make PTC3 pin as GPIO */
    PORTC->PCR[4] = 0x100;      /* make PTC4 pin as GPIO */
    PORTC->PCR[5] = 0x100;      /* make PTC5 pin as GPIO */
    PORTC->PCR[6] = 0x100;      /* make PTC6 pin as GPIO */
    PTC->PDDR |= 0x78;          /* make PTC6-3 as output pin */
    
    rv = I2C1_byteWrite(SLAVE_ADDR, 0, 0);
    if (rv)
        for(;;) ;   /* replace with error handling */

    for (;;)
    {
        rv = I2C1_byteRead(SLAVE_ADDR, 0, &second);
        if (rv)
            for(;;) ;   /* replace with error handling */
        PTC->PDOR = (second & 0xF) << 3;
        delayUs(1000000);
    }
}

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

    SIM->SCGC4 |= 0x80;         /* turn on clock to I2C1 */
    SIM->SCGC5 |= 0x0800;       /* turn on clock to PortC */
    PORTC->PCR[1] = 0x0200;     /* PTE1 I2C1 SCL */
    PORTC->PCR[2] = 0x0200;     /* 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 */
}

/* Write a signle byte to slave memory.
 * write: S-(saddr+w)-ACK-maddr-ACK-data-ACK-P
 */
int I2C1_byteWrite(unsigned char slaveAddr, unsigned char memAddr, unsigned char data) {
    int retry = 1000;

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

    /* send 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 */
        I2C1->S |= 0x10;        /* clear IF */
        return ERR_ARB_LOST;
    }
    if (I2C1->S & 0x01)         /* got NACK from slave */
        return ERR_NO_ACK;

    /* send memory address */
    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;

    /* send data */
    I2C1->D = data;
    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;

    /* stop */
    I2C1->C1 &= ~0x30;

    return ERR_NONE;
}

/* Read a single byte from slave memory.
 * Burst read: S-(saddr+w)-ACK-maddr-ACK-R-(saddr+r)-data-NACK-P
 */
int I2C1_byteRead(unsigned char slaveAddr, unsigned char memAddr, unsigned char* data) {
    int retry = 100;
    volatile unsigned char dummy;

    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 &= ~0x10;          /* Tx off */
    I2C1->C1 |= 0x08;           /* prepare to give NACK */
    dummy = I2C1->D;            /* dummy read to initiate bus read */

    /* read data */
    while(!(I2C1->S & 0x02));   /* wait for transfer complete */
    I2C1->S |= 0x02;            /* clear IF */
    I2C1->C1 &= ~0x20;          /* stop the bus before reading the byte */
    *data = I2C1->D;            /* read received data */

    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++) ;
    }
}