#include <SPI.h>
#include "wiring_private.h" // pinPeripheral() function

// DOCUMENTACIÓN AQUI:
// https://learn.adafruit.com/using-atsamd21-sercom-to-add-more-spi-i2c-serial-ports?view=all
// SPIClass SPI (&PERIPH_SPI,  PIN_SPI_MISO,  PIN_SPI_SCK,  PIN_SPI_MOSI,  PAD_SPI_TX,  PAD_SPI_RX);

// SPI_PAD_0_SCK_1 means MOSI is on SERCOMn.0 and SCK is on SERCOMn.1
// SERCOM_RX_PAD_3 means MISO on SERCOMn.3
SPIClass mySPI (&sercom1, 12, 13, 11, SPI_PAD_0_SCK_1, SERCOM_RX_PAD_3);

void setup() {
  Serial.begin(115200);

  // do this first, for Reasons
  mySPI.begin();

  // Assign pins 11, 12, 13 to SERCOM functionality
  pinPeripheral(11, PIO_SERCOM); // MOSI
  pinPeripheral(12, PIO_SERCOM); // MISO
  pinPeripheral(13, PIO_SERCOM); // SCK
}

uint8_t i=0;
void loop() {
  SerialUSB.println(i);
  mySPI.beginTransaction(SPISettings(8000000, MSBFIRST, SPI_MODE0));
  mySPI.transfer(i++);
  mySPI.endTransaction();
}