/* p8_1.c: Using SERCOM1 to send A to Z characters via SPI
 *
 * SERCOM1 is configured as SPI with hardware Slave Select.
 * Clock rate is set to 500kHz, half of the main clock.
 * Polarity/Phase are 0, 0
 *
 * PA16  PAD0  MOSI
 * PA17  PAD1  SCK
 * PA18  PAD2  SS       hardware controlled
 * PA19  PAD3  MISO
 *
 * Tested with Atmel Studio 7 v7.0.1006 and Keil MDK-ARM v5.21a.
 */

#include "samd21.h"

unsigned char* ARRAY_PORT_PINCFG0 = (unsigned char*)&REG_PORT_PINCFG0;
unsigned char* ARRAY_PORT_PMUX0 = (unsigned char*)&REG_PORT_PMUX0;

int main(void) {
    int c;

    REG_PM_APBCMASK |= 0x00000008;          /* SERCOM1 bus clock */
    REG_GCLK_CLKCTRL = 0x4015;              /* SERCOM1 core clock */

    ARRAY_PORT_PINCFG0[16] |= 1;    /* allow pmux to set PA16 pin configuration */
    ARRAY_PORT_PINCFG0[17] |= 1;    /* allow pmux to set PA17 pin configuration */
    ARRAY_PORT_PINCFG0[18] |= 1;    /* allow pmux to set PA18 pin configuration */
    ARRAY_PORT_PINCFG0[19] |= 1;    /* allow pmux to set PA19 pin configuration */
    ARRAY_PORT_PMUX0[8] = 0x22;     /* PA16 = MOSI, PA17 = SCK */
    ARRAY_PORT_PMUX0[9] = 0x22;     /* PA18 = SS,   PA19 = MISO */

    REG_SERCOM1_SPI_CTRLA = 1;              /* reset SERCOM1 */
    while (REG_SERCOM1_SPI_CTRLA & 1) {}    /* wait for reset to complete */
    REG_SERCOM1_SPI_CTRLA = 0x0030000C;     /* MISO-3, MOSI-0, SCK-1, SS-2, SPI master */
    REG_SERCOM1_SPI_CTRLB = 0x00002000;     /* Master SS, 8-bit */
    REG_SERCOM1_SPI_BAUD = 0;               /* SPI clock is 1MHz/2 = 500kHz */
    REG_SERCOM1_SPI_CTRLA |= 2;             /* enable SERCOM1 */
    
    while(1) {
        for (c = 'A'; c <= 'Z'; c++) {
            while(!(REG_SERCOM1_SPI_INTFLAG & 1)) {}    /* wait until Tx ready */
            REG_SERCOM1_SPI_DATA = c;                   /* send data byte */
        }
    }
}