/*
 * 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 "TM4C123GH6PM.h"

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

#define SLAVE_ADDR 0x68     // 1101 000.

int main(void)
{
    unsigned char readback;
    unsigned char error;

    SYSCTL->RCGCGPIO |= 0x02;   // enable clock to GPIOB
    readback = SYSCTL->RCGCGPIO;
    // enable PORTB 3-0 as output for LEDs
    GPIOB->DIR |= 0x0F;         // set PORTB 3-0 as output pins
    GPIOB->DEN |= 0x0F;         // set PORTB 3-0 as digital pins

    I2C1_init();
    error = I2C1_byteWrite(SLAVE_ADDR, 0, 0);
    if (error)
    {
        GPIOB->DATA = error;
        while(1) ;  // if I2C error, stop here
    }
    
    for (;;)
    {
        error = I2C1_byteRead(SLAVE_ADDR, 0, &readback);
        if (error)
        {
            GPIOB->DATA = error;
            while(1) ;  // if I2C error, stop here
        }
        GPIOB->DATA = readback;
        delayMs(500);
    }
}

void I2C1_init(void)
{
    SYSCTL->RCGCI2C |= 0x02;    // enable clock to I2C1
    SYSCTL->RCGCGPIO |= 0x01;   // enable clock to GPIOA

    // PORTA 7, 6 for I2C1
    GPIOA->AFSEL |= 0xC0;       // PORTA 7, 6 for I2C1
    GPIOA->PCTL &= ~0xFF000000; // PORTA 7, 6 for I2C1
    GPIOA->PCTL |= 0x33000000;
    GPIOA->DEN |= 0xC0;         // PORTA 7, 6 as digital pins
	GPIOA->ODR |= 0x80;         // PORTA 7 as open drain

    I2C1->MCR = 0x10;           // master mode
    I2C1->MTPR = 7;             // 100 kHz @ 16 MHz
}

static int I2C1_wait_till_done(void)
{
    while(I2C1->MCS & 1);       // wait until I2C1 master is not busy
    return I2C1->MCS & 0xE;     // return I2C1 error code
}

// Write one byte
unsigned char I2C1_byteWrite(int slaveAddr, unsigned char memAddr, const unsigned char data)
{
    unsigned char error;

    // write a byte: S-(addr+w)-ACK-memAddr-ACK-data-ACK-P
    I2C1->MSA = slaveAddr << 1;
    I2C1->MDR = memAddr;
    I2C1->MCS = 3;                  // S-(addr+w)-ACK-memAddr-ACK

    error = I2C1_wait_till_done();  // wait until write is complete
    if (error)
        return error;

    I2C1->MDR = data;
    I2C1->MCS = 5;                  // -data-ACK-P
    error = I2C1_wait_till_done();  // wait until write is complete
    while(I2C1->MCS & 0x40);        // wait until bus is not busy
    error = I2C1->MCS & 0xE;
    return error;
}

// Read one byte
unsigned char I2C1_byteRead(int slaveAddr, unsigned char memAddr, unsigned char* data)
{
    unsigned char error;

    // read: S-(addr+w)-ACK-memAddr-ACK-R-(addr+r)-ACK-data-NACK-P
    I2C1->MSA = slaveAddr << 1;
    I2C1->MDR = memAddr;
    I2C1->MCS = 3;                      // S-(addr+w)-ACK-memAddr-ACK
    error = I2C1_wait_till_done();
    if (error)
        return error;

    I2C1->MSA = (slaveAddr << 1) + 1;   // restart: -R-(addr+r)-ACK
    I2C1->MCS = 7;                      // -S-(addr+r)-NACK-P
    error = I2C1_wait_till_done();
    if (error)
        return error;

    *data = I2C1->MDR;

    while(I2C1->MCS & 0x40);            // wait until bus is not busy
    error = I2C1->MCS & 0xE;
    
    return error;
}

// delay n milliseconds (16 MHz CPU clock)
void delayMs(int n)
{
    int i, j;
    for(i = 0 ; i < n; i++)
        for(j = 0; j < 3180; j++)
            {}  // do nothing for 1 ms
}

// delay n microseconds (16 MHz CPU clock)
void delayUs(int n)
{
    int i, j;
    for(i = 0 ; i < n; i++)
        for(j = 0; j < 3; j++)
            {}  // do nothing for 1 ms
}


// This function is called by the startup assembly
// code to perform system specific initialization tasks.
void SystemInit(void)
{
    // Grant coprocessor access
    // This is required since TM4C123G has
    // a floating point coprocessor
    SCB->CPACR |= 0x00f00000;
}