/* p8_2.c: Using SPI to send A to Z characters via SPI
 * UCB0 is configured as SPI. Software controlled slave select.
 *
 * P1.5 UCB0CLK
 * P1.6 UCB0SIMO
 * P2.3 Slave Select
 *
 * Tested with Keil 5.20 and MSP432 Device Family Pack V2.2.0.
 */

#include "msp.h"

void delayMs(int n);

int main(void) {
    int c;

    EUSCI_B0->CTLW0 = 0x0001;     /* disable UCB0 during config */
    /* clock phase/polarity:11, MSB first, 8-bit, master, 3-pin SPI,
       synchronous mode, use SMCLK as clock source */
    EUSCI_B0->CTLW0 = 0xE9C1;
    EUSCI_B0->BRW = 1;            /* 3 MHz / 1 = 3 MHz */
    EUSCI_B0->CTLW0 &= ~0x0001;   /* enable UCB0 after config */

    P1->SEL0 |= 0x60;         /* P1.5, P1.6 for UCB0CLK, UCB0SIMO */
    P1->SEL1 &= ~0x60;

    P2->DIR |= 8;             /* P2.3 set as output for slave select */
    P2->OUT |= 8;             /* slave select idle high */

    while(1)
    {
        for (c = 'A'; c <= 'Z'; c++) {
            P2->OUT &= ~8;                /* assert slave select */

            while(!(EUSCI_B0->IFG & 2)) ;     /* wait for transmit buffer empty */
            EUSCI_B0->TXBUF = c;              /* write to SPI transmit buffer */

            while(EUSCI_B0->STATW & 1) ;      /* wait for transmit done */
            P2->OUT |= 8;                 /* deassert slave select */
            delayMs(10);
        }
    }
}

/* system clock at 3 MHz */
void delayMs(int n) {
    int i, j;
    
    for (j = 0; j < n; j++)
        for (i = 250; i > 0; i--);      /* delay 1 ms */
}