/*P8_2.c: Programming MAX7219 via SPI with FRDM-KL25Z 

 * MAX7219 is connected to a two-digit seven-segment LED
 * The program displays "57" on the seven-segment LED
 * PTD1 pin as SPI SCK 
 * PTD2 pin as SPI MOSI
 * PTD0 pin as chip select
 */ 
 
#include "MKL25Z4.h"

void SPI0_init(void);
void SPI0_write(unsigned char data);
void max7219_write(unsigned char command, unsigned char data);

#define DECODE 9
#define INTENSITY 10
#define SCANLIMIT 11
#define SHUTDOWN 12
#define TEST 15

int main(void) {
    SPI0_init();                 /* enable SPI0 */
    
    max7219_write(DECODE, 3);    /* enable decode for digit 1, 0 */
    max7219_write(SCANLIMIT, 2); /* scan two digits */
    max7219_write(INTENSITY, 4); /* set 1/4 intensity */
    max7219_write(TEST, 0);      /* disable test mode */
    max7219_write(SHUTDOWN, 1);  /* enable device */
    max7219_write(0x02, 5);      /* display 5 */
    max7219_write(0x01, 7);      /* display 7 */

    while(1) {
    }
}

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 CS */
    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 max7219_write(unsigned char command, unsigned char data) {
    volatile char dummy;
    
    PTD->PCOR = 1;                  /* assert /CS */

    while(!(SPI0->S & 0x20)) { }    /* wait until tx ready */
    SPI0->D = command;              /* send command byte first */
    while(!(SPI0->S & 0x80)) { }    /* wait until tx complete */
    dummy = SPI0->D;                /* clear SPRF */
    
    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;                  /* de-assert /CS */
}