/* p8_1.c: Using SPI to send A to Z characters via SPI
 * UCA1 is configured as 4-pin SPI.
 * Because MSP432 has no SPI with all 4 pins brought out
 * to the 40-pin headers, Pin Map is used to redirect them:
 * P2.3 CLK
 * P2.4 SIMO
 * P2.5 STE
 *
 * Tested with Keil 5.20 and MSP432 Device Family Pack V2.2.0.
 */

#include "msp.h"

void delayMs(int n);

int main(void) {
    int i;

    EUSCI_A1->CTLW0 = 0x0001;         /* disable UCA1 during config */
    /* clock phase/polarity:11, MSB first, 8-bit, master, 4-pin SPI, STE low active,
       synchronous mode, use SMCLK as clock source, STE for slave enable */
    EUSCI_A1->CTLW0 = 0xEDC3;
    EUSCI_A1->BRW = 1;                /* 3 MHz / 1 = 3 MHz */
    EUSCI_A1->CTLW0 &= ~0x0001;       /* enable UCA1 after config */

    PMAP->KEYID = 0x2D52;      /* unlock PMAP */
    P2MAP->PMAP_REGISTER[1] = 0x0800;    /* map P2.3 to PM_UCA1CLK */
    P2MAP->PMAP_REGISTER[2] = 0x070A;    /* map P2.4 to PM_UCA1SIMO, map P2.5 to PM_UCA1STE */
    P2->SEL0 |= 0x38;               /* set alternate function to pinmap */
    P2->SEL1 &= ~0x38;              /* for P2.3, P2.4, P2.5 */
    PMAP->CTL = 0;                  /* lock PMAP */
    PMAP->KEYID = 0;

    while(1) {
        for (i = 'A'; i <= 'Z'; i++) {
            while(!(EUSCI_A1->IFG & 2)) ; /* wait for transmit buffer empty */
            EUSCI_A1->TXBUF = i;          /* write the character */
            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 */
}