/* OLED_SSD1306 via I2C
 *
 * This program communicate with the OLED_SSD1306 via I2C.
 * It writes "ABC" on the display and fills the rest of the
 * display with a checker board pattern.
 *
 * I2C1SCL P6.5
 * I2C1SDA P6.4
 *
 * Built and tested with MSP432P401R Rev. C, Keil MDK-ARM v5.24a and MSP432P4xx_DFP v3.1.0
 */

#include "msp.h"

#define SLAVE_ADDR 0x3C     // 0111 100.
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define SCREEN_PAGE_NUM (SCREEN_HEIGHT / 8)

void delayMs(int n);
void I2C1_init(void);
int I2C1_byteWrite(int slaveAddr, unsigned char memAddr, unsigned char data);
void SSD1306_init(void);
void SSD1306_data(char data);
void SSD1306_command(char command);
char imagebuf[SCREEN_PAGE_NUM][SCREEN_WIDTH];

const static char font_table[][6] = {    /* sample font table */
    {0x7e, 0x11, 0x11, 0x11, 0x7e, 0},  /* A */
    {0x7f, 0x49, 0x49, 0x49, 0x36, 0},  /* B */
    {0x3e, 0x41, 0x41, 0x41, 0x22, 0}}; /* C */

int main(void) {
    int i, j, k;

    I2C1_init();
    SSD1306_init();

    SSD1306_command(0x22);              /* set page */
    SSD1306_command(0x00);              /* starting page */
    SSD1306_command(0x00);              /* end page */
    SSD1306_command(0x21);              /* set column */
    SSD1306_command(0);                 /* starting column */
    SSD1306_command(SCREEN_WIDTH-1);    /* end column */
    
    /* write ABC at the beginning of first line */
    for (j = 0; j < 3; j++)
        for (i = 0; i < 6; i++)
            SSD1306_data(font_table[j][i]);

    /* clear the rest of the line */
    for (i = 0; i < SCREEN_WIDTH-3*6; i++)
        SSD1306_data(0);

    for (i = 1; i < SCREEN_PAGE_NUM; i++) {
        SSD1306_command(0x22);              /* set page */
        SSD1306_command(i);                 /* starting page */
        SSD1306_command(i);                 /* end page */
        SSD1306_command(0x21);              /* set column */
        SSD1306_command(0);                 /* starting column */
        SSD1306_command(SCREEN_WIDTH-1);    /* end column */

        /* make checker board pattern */
        for (j = 0; j < SCREEN_WIDTH/8; j++) {
            for (k = 0; k < 4; k++)
                SSD1306_data(0xF0);

            for (k = 0; k < 4; k++)
                SSD1306_data(0x0F);
        }
    }

    for (;;) {  /* infinite loop */
    }
}

/* system clock at 3 MHz, MSP432P401R Rev. C, Start-up v2.2.1 */
void delayMs(int n) {
    int i, j;
    
    for (j = 0; j < n; j++)
        for (i = 750; i > 0; i--);      /* Delay */
}

/* configure UCB1 as I2C */
void I2C1_init(void) {
    extern uint32_t SystemCoreClock;
    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 for 100kHz */
    P6->SEL0 |= 0x30;               /* P6.5, P6.4 for UCB1 */
    P6->SEL1 &= ~0x30;
    EUSCI_B1->CTLW0 &= ~1;          /* enable UCB1 after config */
}

/* Write a single byte at memAddr
 * write: S-(slaveAddr+w)-ACK-memAddr-ACK-data-ACK-P
 */
int I2C1_byteWrite(int slaveAddr, unsigned char memAddr, unsigned char data) {
    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 it's ready to transmit */
    EUSCI_B1->TXBUF = data;         /* send data to slave */
    while(!(EUSCI_B1->IFG & 2));    /* wait till last transmit is done */
    EUSCI_B1->CTLW0 |= 0x0004;      /* send STOP */
    while(EUSCI_B1->CTLW0 & 4) ;    /* wait until STOP is sent */
    return 0;
}

const static char init_seq[] = {
    0xae,       // turn off oled panel
    0x00,       // set low column address
    0x10,       // set high column address
    0x40,       // set start line address
    0x20, 0x02, // page addressing mode
    0xc8,       // top-down segment (4th quadrant)
    0x81,       // set contrast control register
    0xcf, 0xa1, // set segment re-map 95 to 0
    0xa6,       // set normal display
    0xa8,       // set multiplex ratio(1 to 64)
    0x3f,       // 1/64 duty
    0xd3,       // set display offset
    0x00,       // not offset
    0xd5,       // set display clock divide ratio/oscillator frequency
    0x80,       // set divide ratio
    0xd9,       // set pre-charge period
    0xf1, 0xda, // set com pins hardware configuration
    0x12, 0xdb, // set vcomh
    0x40, 0x8d, // set Charge Pump enable/disable
    0x14,       // set(0x10) disable
    0xaf        // turn on oled panel
};

void SSD1306_init(void) {
    int i;

    delayMs(100);

	for (i = 0; i < sizeof(init_seq); i++)
        SSD1306_command(init_seq[i]);
}

void SSD1306_data(char data) {
    I2C1_byteWrite(SLAVE_ADDR, 0xC0, data);
}

void SSD1306_command(char command) {
    I2C1_byteWrite(SLAVE_ADDR, 0x80, command);
}