/* Seven-segment display counter
 *
 * This program counts number 0-3 on the seven segment display.
 * The seven segment display is driven by a shift register which is
 * connected to UCB0 in SPI mode.
 *
 * Built and tested with MSP432P401R Rev. C, Keil MDK-ARM v5.24a and MSP432P4xx_DFP v3.1.0
 */

#include "msp.h"

void delayMs(int n);
void sevenseg_init(void);
void UCB0_write(unsigned char data);

int main(void) {
    const static unsigned char digitPattern[] = {0x3F, 0x06, 0x5B, 0x4F};
    static int i;

    sevenseg_init();    /* initialize UCB0 that connects to the shift registers */

    while(1) {
        UCB0_write(~digitPattern[i]);   /* write digit pattern to the seven segments */
        if (++i > 3)
            i = 0;

        delayMs(1000);
    }
}

/* configure UCB0 and associated GPIO pins */
void sevenseg_init(void) {
    EUSCI_B0->CTLW0 = 0x0001;           /* soft reset */
    EUSCI_B0->CTLW0 = 0xE9C1;           /* SPI master PH=1, PL=1 */
    EUSCI_B0->CTLW0 &= ~0x0001;         /* out of reset */

    P1->SEL0 |= (1 << 5) | (1 << 6);    /* P1.5, P1.6 for UCB0 */
    P1->SEL1 &= ~((1 << 5) | (1 << 6));

    /* P2.3 as slave select */
    P2->DIR |= 1 << 3;                  /* P2.3 set as output */
    P2->OUT |= 1 << 3;                  /* /SS idle high */
}

/* This function enables slave select, writes one byte to UCB0, */
/* wait for transmit complete and deassert slave select. */
void UCB0_write(unsigned char data) {
    P2->OUT &= ~(1 << 3);                 /* assert slave select */
    EUSCI_B0->TXBUF = data;               /* write data */
    while(EUSCI_B0->STATW & 0x01) ;       /* wait for transmit done */
    P2->OUT |= 1 << 3;                    /* deassert slave select */
}

/* 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 */
}