/* p9_4.c: burst read from DS1337
 *
 * This program reads the first seven registers of DS1337 using
 * burst read. 
 * After the first read, the register address pointer automatically
 * incremented to point to the next register and the 
 * subsequent read comes from the next register. Before the last
 * read, a STOP is setup to be generated when the read is complete.
 * The three least significant bits of the second counter are used to 
 * turn on/off the tri-color LEDs on the LaunchPad board.
 * P6.5 - SCL, P6.4 - SDA
 *
 * You can modify this program to send data via serial COM port 
 * to the PC screen (Teraterminal) or display it on the text LCD.
 *
 * No error checking is done in I2C code.
 * 
 * Tested with Keil 5.20 and MSP432 Device Family Pack V2.2.0
 * on XMS432P401R Rev C.
 */

#include <stdio.h>
#include "msp.h"

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

#define SLAVE_ADDR 0x68     // 1101 000.    DS1337

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

    P2->DIR |= 7;   /* P2.2, P2.1 ,P2.0 set as output for tri-color LEDs */

    I2C1_init();

    for (;;) {
        /* read the first seven bytes of the registers */
        I2C1_burstRead(SLAVE_ADDR, 0, 7, timeDateReadback);
        P2->OUT = timeDateReadback[0];    /* write second count to LEDs */
        delayMs(237);                   /* delay arbitrary time */
    }
}

/* configure UCB1 as I2C */
void I2C1_init(void) {
    EUSCI_B1->CTLW0 |= 1;             /* disable UCB1 during config */
    EUSCI_B1->CTLW0 = 0x0F81;         /* 7-bit slave addr, master, I2C, synch mode, use SMCLK */
    EUSCI_B1->BRW = 30;               /* set clock prescaler 3MHz / 30 = 100kHz */
    P6->SEL0 |= 0x30;             /* P6.5, P6.4 for UCB1 */
    P6->SEL1 &= ~0x30;
    EUSCI_B1->CTLW0 &= ~1;            /* enable UCB1 after config */
}

/* Use burst read to read multiple bytes from consecutive locations
 * read: S-(slaveAddr+w)-ACK-memAddr-ACK-R-(slaveAddr+r)-ACK-data-ACK-...-data-NACK-P
 */
int I2C1_burstRead(int slaveAddr, unsigned char memAddr, int byteCount, unsigned char* data) {
    if (byteCount <= 0)
        return -1;              /* no read was performed */

    EUSCI_B1->I2CSA = slaveAddr;      /* setup slave address */
    EUSCI_B1->CTLW0 |= 0x0010;        /* enable transmitter */
    EUSCI_B1->CTLW0 |= 0x0002;        /* generate START and send slave address */
    while((EUSCI_B1->CTLW0 & 2));   /* wait until slave address is sent */
    EUSCI_B1->TXBUF = memAddr;        /* send memory address to slave */
    while(!(EUSCI_B1->IFG & 2));      /* wait till last transmit is done */
    EUSCI_B1->CTLW0 &= ~0x0010;       /* enable receiver */
    EUSCI_B1->CTLW0 |= 0x0002;        /* generate RESTART and send slave address */
    while(EUSCI_B1->CTLW0 & 2);       /* wait till RESTART is finished */

    /* receive data one byte at a time */
    do {
        if (byteCount == 1)     /* when only one byte of data is left */
            EUSCI_B1->CTLW0 |= 0x0004; /* setup to send STOP after the last byte is received */

        while(!(EUSCI_B1->IFG & 1));  /* wait till data is received */
        *data++ = EUSCI_B1->RXBUF;    /* read the received data */
        byteCount--;
    } while (byteCount);

    while(EUSCI_B1->CTLW0 & 4) ;      /* wait until STOP is sent */

    return 0;                   /* no error */
}

/* system clock at 3 MHz */
void delayMs(int n) {
    int i, j;

    for (j = 0; j < n; j++)
        for (i = 750; i > 0; i--);      /* delay 1 ms */
}