/*P8_1.c: Send 'A' to 'Z' via SPI0

 * PTD1 pin as SPI SCK 
 * PTD2 pin as SPI MOSI
 * PTD0 pin as SPI SS
 */ 
 
#include "MKL25Z4.h"

void SPI0_init(void);
void SPI0_write(unsigned char data);

int main(void) {
    unsigned char c;
    
    SPI0_init();                 /* enable SPI0 */
    
    while(1) {
        for(c = 'A'; c <= 'Z'; c++) {
            SPI0_write(c);
        }
    }
}

void SPI0_init(void) {
    SIM->SCGC5 |= 0x1000;       /* enable clock to Port D */
    PORTD->PCR[1] = 0x200;      /* make PTD1 pin as SPI SCK */
    PORTD->PCR[2] = 0x200;      /* make PTD2 pin as SPI MOSI */
    PORTD->PCR[0] = 0x100;      /* make PTD0 pin as GPIO */
    PTD->PDDR |= 0x01;          /* make PTD0 as output pin for /SS */
    PTD->PSOR = 0x01;           /* make PTD0 idle high */
    
    SIM->SCGC4 |= 0x400000;     /* enable clock to SPI0 */
    SPI0->C1 = 0x10;            /* disable SPI and make SPI0 master */
    SPI0->BR = 0x60;            /* set Baud rate to 1 MHz */
    SPI0->C1 |= 0x40;           /* Enable SPI module */
}

void SPI0_write(unsigned char data) {
    volatile char dummy;
    
    PTD->PCOR = 1;                  /* assert /SS */
    
    while(!(SPI0->S & 0x20)) { }    /* wait until tx ready */
    SPI0->D = data;                 /* send data byte */
    while(!(SPI0->S & 0x80)) { }    /* wait until tx complete */
    dummy = SPI0->D;                /* clear SPRF */
    
    PTD->PSOR = 1;                  /* deassert /SS */
}