muele-marlin/Marlin/src/HAL/HAL_DUE/HAL_spi_Due.cpp

/**
 * Marlin 3D Printer Firmware
 * Copyright (C) 2016 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
 *
 * Based on Sprinter and grbl.
 * Copyright (C) 2011 Camiel Gubbels / Erik van der Zalm
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

/**
 * Software SPI functions originally from Arduino Sd2Card Library
 * Copyright (C) 2009 by William Greiman
 *
 * Completely rewritten and tuned by Eduardo José Tagle in 2017/2018
 * in ARM thumb2 inline assembler and tuned for maximum speed and performance
 * allowing SPI clocks of up to 12 Mhz to increase SD card read/write performance
 */

/**
 * Description: HAL for Arduino Due and compatible (SAM3X8E)
 *
 * For ARDUINO_ARCH_SAM
 */

#ifdef ARDUINO_ARCH_SAM

// --------------------------------------------------------------------------
// Includes
// --------------------------------------------------------------------------

#include "../../inc/MarlinConfig.h"

// --------------------------------------------------------------------------
// Public Variables
// --------------------------------------------------------------------------


// --------------------------------------------------------------------------
// Public functions
// --------------------------------------------------------------------------

#if ENABLED(SOFTWARE_SPI)
  // --------------------------------------------------------------------------
  // software SPI
  // --------------------------------------------------------------------------

  // set optimization so ARDUINO optimizes this file
  #pragma GCC optimize (3)

  /* ---------------- Delay Cycles routine -------------- */

  /* https://blueprints.launchpad.net/gcc-arm-embedded/+spec/delay-cycles */

  #define nop() __asm__ __volatile__("nop;\n\t":::)

  FORCE_INLINE static void __delay_4cycles(uint32_t cy) { // +1 cycle
    #if ARCH_PIPELINE_RELOAD_CYCLES<2
      #define EXTRA_NOP_CYCLES "nop"
    #else
      #define EXTRA_NOP_CYCLES ""
    #endif

    __asm__ __volatile__(
      ".syntax unified" "\n\t" // is to prevent CM0,CM1 non-unified syntax

      "loop%=:" "\n\t"
      " subs %[cnt],#1" "\n\t"
      EXTRA_NOP_CYCLES "\n\t"
      " bne loop%=" "\n\t"
      : [cnt]"+r"(cy) // output: +r means input+output
      : // input:
      : "cc" // clobbers:
    );
  }

  FORCE_INLINE static void DELAY_CYCLES(uint32_t x) {

    if (__builtin_constant_p(x)) {

      #define MAXNOPS 4

      if (x <= (MAXNOPS)) {
        switch(x) { case 4: nop(); case 3: nop(); case 2: nop(); case 1: nop(); }
      }
      else { // because of +1 cycle inside delay_4cycles
        const uint32_t rem = (x - 1) % (MAXNOPS);
        switch(rem) { case 3: nop(); case 2: nop(); case 1: nop(); }
        if ((x = (x - 1) / (MAXNOPS)))
          __delay_4cycles(x); // if need more then 4 nop loop is more optimal
      }
    }
    else
      __delay_4cycles(x / 4);
  }

  /* ---------------- Delay in nanoseconds and in microseconds */

  #define DELAY_NS(x) DELAY_CYCLES( (x) * (F_CPU/1000000) / 1000)

  typedef uint8_t (*pfnSpiTransfer) (uint8_t b);

  /* ---------------- Macros to be able to access definitions from asm */

  #define _PORT(IO) DIO ##  IO ## _WPORT
  #define _PIN_MASK(IO) MASK(DIO ## IO ## _PIN)
  #define _PIN_SHIFT(IO) DIO ## IO ## _PIN
  #define PORT(IO) _PORT(IO)
  #define PIN_MASK(IO) _PIN_MASK(IO)
  #define PIN_SHIFT(IO) _PIN_SHIFT(IO)

  // run at ~8 .. ~10Mhz - Tx version (Rx data discarded)
  static uint8_t spiTransferTx0(uint8_t bout) { // using Mode 0
    register uint32_t MOSI_PORT_PLUS30 = ((uint32_t) PORT(MOSI_PIN)) + 0x30;  /* SODR of port */
    register uint32_t MOSI_MASK = PIN_MASK(MOSI_PIN);
    register uint32_t SCK_PORT_PLUS30 = ((uint32_t) PORT(SCK_PIN)) + 0x30;    /* SODR of port */
    register uint32_t SCK_MASK = PIN_MASK(SCK_PIN);
    register uint32_t idx;

    /* Negate bout, as the assembler requires a negated value */
    bout = ~bout;

    /* The software SPI routine */
    __asm__ __volatile__(
      ".syntax unified" "\n\t" // is to prevent CM0,CM1 non-unified syntax

      /* Bit 7 */
      " ubfx %[idx],%[txval],#7,#1" "\n\t"                      /* Place bit 7 in bit 0 of idx*/

      " str %[mosi_mask],[%[mosi_port], %[idx],LSL #2]" "\n\t"  /* Access the proper SODR or CODR registers based on that bit */
      " str %[sck_mask],[%[sck_port]]" "\n\t"                   /* SODR */
      " ubfx %[idx],%[txval],#6,#1" "\n\t"                      /* Place bit 6 in bit 0 of idx*/
      " str %[sck_mask],[%[sck_port],#0x4]" "\n\t"              /* CODR */

      /* Bit 6 */
      " str %[mosi_mask],[%[mosi_port], %[idx],LSL #2]" "\n\t"  /* Access the proper SODR or CODR registers based on that bit */
      " str %[sck_mask],[%[sck_port]]" "\n\t"                   /* SODR */
      " ubfx %[idx],%[txval],#5,#1" "\n\t"                      /* Place bit 5 in bit 0 of idx*/
      " str %[sck_mask],[%[sck_port],#0x4]" "\n\t"              /* CODR */

      /* Bit 5 */
      " str %[mosi_mask],[%[mosi_port], %[idx],LSL #2]" "\n\t"  /* Access the proper SODR or CODR registers based on that bit */
      " str %[sck_mask],[%[sck_port]]" "\n\t"                   /* SODR */
      " ubfx %[idx],%[txval],#4,#1" "\n\t"                      /* Place bit 4 in bit 0 of idx*/
      " str %[sck_mask],[%[sck_port],#0x4]" "\n\t"              /* CODR */

      /* Bit 4 */
      " str %[mosi_mask],[%[mosi_port], %[idx],LSL #2]" "\n\t"  /* Access the proper SODR or CODR registers based on that bit */
      " str %[sck_mask],[%[sck_port]]" "\n\t"                   /* SODR */
      " ubfx %[idx],%[txval],#3,#1" "\n\t"                      /* Place bit 3 in bit 0 of idx*/
      " str %[sck_mask],[%[sck_port],#0x4]" "\n\t"              /* CODR */

      /* Bit 3 */
      " str %[mosi_mask],[%[mosi_port], %[idx],LSL #2]" "\n\t"  /* Access the proper SODR or CODR registers based on that bit */
      " str %[sck_mask],[%[sck_port]]" "\n\t"                   /* SODR */
      " ubfx %[idx],%[txval],#2,#1" "\n\t"                      /* Place bit 2 in bit 0 of idx*/
      " str %[sck_mask],[%[sck_port],#0x4]" "\n\t"              /* CODR */

      /* Bit 2 */
      " str %[mosi_mask],[%[mosi_port], %[idx],LSL #2]" "\n\t"  /* Access the proper SODR or CODR registers based on that bit */
      " str %[sck_mask],[%[sck_port]]" "\n\t"                   /* SODR */
      " ubfx %[idx],%[txval],#1,#1" "\n\t"                      /* Place bit 1 in bit 0 of idx*/
      " str %[sck_mask],[%[sck_port],#0x4]" "\n\t"              /* CODR */

      /* Bit 1 */
      " str %[mosi_mask],[%[mosi_port], %[idx],LSL #2]" "\n\t"  /* Access the proper SODR or CODR registers based on that bit */
      " str %[sck_mask],[%[sck_port]]" "\n\t"                   /* SODR */
      " ubfx %[idx],%[txval],#0,#1" "\n\t"                      /* Place bit 0 in bit 0 of idx*/
      " str %[sck_mask],[%[sck_port],#0x4]" "\n\t"              /* CODR */

      /* Bit 0 */
      " str %[mosi_mask],[%[mosi_port], %[idx],LSL #2]" "\n\t"  /* Access the proper SODR or CODR registers based on that bit */
      " str %[sck_mask],[%[sck_port]]" "\n\t"                   /* SODR */
      " nop"  "\n\t"
      " str %[sck_mask],[%[sck_port],#0x4]" "\n\t"              /* CODR */

      : [mosi_mask]"+r"( MOSI_MASK ),
        [mosi_port]"+r"( MOSI_PORT_PLUS30 ),
        [sck_mask]"+r"( SCK_MASK ),
        [sck_port]"+r"( SCK_PORT_PLUS30 ),
        [idx]"+r"( idx ),
        [txval]"+r"( bout )
      :
      : "cc"
    );

    return 0;
  }

  // run at ~8 .. ~10Mhz - Rx version (Tx line not altered)
  static uint8_t spiTransferRx0(uint8_t bout) { // using Mode 0
    int bin = 0, work = 0;
    register uint32_t MISO_PORT_PLUS3C = ((uint32_t) PORT(MISO_PIN)) + 0x3C;  /* PDSR of port */
    register uint32_t SCK_PORT_PLUS30 = ((uint32_t) PORT(SCK_PIN)) + 0x30;    /* SODR of port */
    register uint32_t SCK_MASK = PIN_MASK(SCK_PIN);
    UNUSED(bout);

    /* The software SPI routine */
    __asm__ __volatile__(
      ".syntax unified" "\n\t" // is to prevent CM0,CM1 non-unified syntax

      /* bit 7 */
      " str %[sck_mask],[%[sck_port]]" "\n\t"           /* SODR */
      " ldr %[work],[%[miso_port]]" "\n\t"              /* PDSR */
      " str %[sck_mask],[%[sck_port],#0x4]" "\n\t"      /* CODR */
      " lsrs %[work],%[work],%[miso_shift]" "\n\t"      /* Isolate input into carry */
      " adc %[bin],%[bin],%[bin]" "\n\t"                /* Shift left result and add the carry */

      /* bit 6 */
      " str %[sck_mask],[%[sck_port]]" "\n\t"           /* SODR */
      " ldr %[work],[%[miso_port]]" "\n\t"              /* PDSR */
      " str %[sck_mask],[%[sck_port],#0x4]" "\n\t"      /* CODR */
      " lsrs %[work],%[work],%[miso_shift]" "\n\t"      /* Isolate input into carry */
      " adc %[bin],%[bin],%[bin]" "\n\t"                /* Shift left result and add the carry */

      /* bit 5 */
      " str %[sck_mask],[%[sck_port]]" "\n\t"           /* SODR */
      " ldr %[work],[%[miso_port]]" "\n\t"              /* PDSR */
      " str %[sck_mask],[%[sck_port],#0x4]" "\n\t"      /* CODR */
      " lsrs %[work],%[work],%[miso_shift]" "\n\t"      /* Isolate input into carry */
      " adc %[bin],%[bin],%[bin]" "\n\t"                /* Shift left result and add the carry */

      /* bit 4 */
      " str %[sck_mask],[%[sck_port]]" "\n\t"           /* SODR */
      " ldr %[work],[%[miso_port]]" "\n\t"              /* PDSR */
      " str %[sck_mask],[%[sck_port],#0x4]" "\n\t"      /* CODR */
      " lsrs %[work],%[work],%[miso_shift]" "\n\t"      /* Isolate input into carry */
      " adc %[bin],%[bin],%[bin]" "\n\t"                /* Shift left result and add the carry */

      /* bit 3 */
      " str %[sck_mask],[%[sck_port]]" "\n\t"           /* SODR */
      " ldr %[work],[%[miso_port]]" "\n\t"              /* PDSR */
      " str %[sck_mask],[%[sck_port],#0x4]" "\n\t"      /* CODR */
      " lsrs %[work],%[work],%[miso_shift]" "\n\t"      /* Isolate input into carry */
      " adc %[bin],%[bin],%[bin]" "\n\t"                /* Shift left result and add the carry */

      /* bit 2 */
      " str %[sck_mask],[%[sck_port]]" "\n\t"           /* SODR */
      " ldr %[work],[%[miso_port]]" "\n\t"              /* PDSR */
      " str %[sck_mask],[%[sck_port],#0x4]" "\n\t"      /* CODR */
      " lsrs %[work],%[work],%[miso_shift]" "\n\t"      /* Isolate input into carry */
      " adc %[bin],%[bin],%[bin]" "\n\t"                /* Shift left result and add the carry */

      /* bit 1 */
      " str %[sck_mask],[%[sck_port]]" "\n\t"           /* SODR */
      " ldr %[work],[%[miso_port]]" "\n\t"              /* PDSR */
      " str %[sck_mask],[%[sck_port],#0x4]" "\n\t"      /* CODR */
      " lsrs %[work],%[work],%[miso_shift]" "\n\t"      /* Isolate input into carry */
      " adc %[bin],%[bin],%[bin]" "\n\t"                /* Shift left result and add the carry */

      /* bit 0 */
      " str %[sck_mask],[%[sck_port]]" "\n\t"           /* SODR */
      " ldr %[work],[%[miso_port]]" "\n\t"              /* PDSR */
      " str %[sck_mask],[%[sck_port],#0x4]" "\n\t"      /* CODR */
      " lsrs %[work],%[work],%[miso_shift]" "\n\t"      /* Isolate input into carry */
      " adc %[bin],%[bin],%[bin]" "\n\t"                /* Shift left result and add the carry */

      : [miso_port]"+r"( MISO_PORT_PLUS3C ),
        [sck_mask]"+r"( SCK_MASK ),
        [sck_port]"+r"( SCK_PORT_PLUS30 ),
        [bin]"+r"(bin),
        [work]"+r"(work)
      : [miso_shift]"M"( PIN_SHIFT(MISO_PIN) + 1 )      /* So we move to the carry */
      : "cc"
    );

    return (uint8_t)bin;
  }

  // run at ~4Mhz
  static uint8_t spiTransfer1(uint8_t b) { // using Mode 0
    int bits = 8;
    do {
      WRITE(MOSI_PIN, b & 0x80);
      b <<= 1;        // little setup time

      WRITE(SCK_PIN, HIGH);
      DELAY_NS(125);  // 10 cycles @ 84mhz

      b |= (READ(MISO_PIN) != 0);

      WRITE(SCK_PIN, LOW);
      DELAY_NS(125);  // 10 cycles @ 84mhz
    } while (--bits);
    return b;
  }

  // all the others
  static uint32_t spiDelayCyclesX4 = (F_CPU/1000000); // 4uS => 125khz

  static uint8_t spiTransferX(uint8_t b) { // using Mode 0
    int bits = 8;
    do {
      WRITE(MOSI_PIN, b & 0x80);
      b <<= 1; // little setup time

      WRITE(SCK_PIN, HIGH);
      __delay_4cycles(spiDelayCyclesX4);

      b |= (READ(MISO_PIN) != 0);

      WRITE(SCK_PIN, LOW);
      __delay_4cycles(spiDelayCyclesX4);
    } while (--bits);
    return b;
  }

  // Pointers to generic functions
  static pfnSpiTransfer spiTransferTx = spiTransferX;
  static pfnSpiTransfer spiTransferRx = spiTransferX;

  void spiBegin() {
    SET_OUTPUT(SS_PIN);
    WRITE(SS_PIN, HIGH);
    SET_OUTPUT(SCK_PIN);
    SET_INPUT(MISO_PIN);
    SET_OUTPUT(MOSI_PIN);
  }

  /**
   * spiRate should be
   *  0 :  8 - 10 MHz
   *  1 :  4 - 5 MHz
   *  2 :  2 - 2.5 MHz
   *  3 :  1 - 1.25 MHz
   *  4 :  500 - 625 kHz
   *  5 :  250 - 312 kHz
   *  6 :  125 - 156 kHz
   */
  void spiInit(uint8_t spiRate) {
    switch (spiRate) {
      case 0:
        spiTransferTx = spiTransferTx0;
        spiTransferRx = spiTransferRx0;
        break;
      case 1:
        spiTransferTx = spiTransfer1;
        spiTransferRx = spiTransfer1;
        break;
      default:
        spiDelayCyclesX4 = (F_CPU/1000000) >> (6 - spiRate);
        spiTransferTx = spiTransferX;
        spiTransferRx = spiTransferX;
        break;
    }

    WRITE(SS_PIN, HIGH);
    WRITE(MOSI_PIN, HIGH);
    WRITE(SCK_PIN, LOW);
  }

  uint8_t spiRec() {
    WRITE(SS_PIN, LOW);
    WRITE(MOSI_PIN, 1); /* Output 1s 1*/
    uint8_t b = spiTransferRx(0xFF);
    WRITE(SS_PIN, HIGH);
    return b;
  }

  void spiRead(uint8_t* buf, uint16_t nbyte) {
    if (nbyte == 0) return;
    WRITE(SS_PIN, LOW);
    WRITE(MOSI_PIN, 1); /* Output 1s 1*/
    for (int i = 0; i < nbyte; i++) {
      buf[i] = spiTransferRx(0xff);
    }
    WRITE(SS_PIN, HIGH);
  }

  void spiSend(uint8_t b) {
    WRITE(SS_PIN, LOW);
    (void) spiTransferTx(b);
    WRITE(SS_PIN, HIGH);
  }

  void spiSendBlock(uint8_t token, const uint8_t* buf) {

    WRITE(SS_PIN, LOW);
    (void) spiTransferTx(token);

    for (uint16_t i = 0; i < 512; i++) {
      (void) spiTransferTx(buf[i]);
    }
    WRITE(SS_PIN, HIGH);
  }

  #pragma GCC reset_options

#else
  // --------------------------------------------------------------------------
  // hardware SPI
  // --------------------------------------------------------------------------
  // 8.4 MHz, 4 MHz, 2 MHz, 1 MHz, 0.5 MHz, 0.329 MHz, 0.329 MHz
  int spiDueDividors[] = { 10, 21, 42, 84, 168, 255, 255 };
  bool spiInitMaded = false;

  void spiBegin() {
    if(spiInitMaded == false) {
      // Configure SPI pins
      PIO_Configure(
         g_APinDescription[SCK_PIN].pPort,
         g_APinDescription[SCK_PIN].ulPinType,
         g_APinDescription[SCK_PIN].ulPin,
         g_APinDescription[SCK_PIN].ulPinConfiguration);
      PIO_Configure(
         g_APinDescription[MOSI_PIN].pPort,
         g_APinDescription[MOSI_PIN].ulPinType,
         g_APinDescription[MOSI_PIN].ulPin,
         g_APinDescription[MOSI_PIN].ulPinConfiguration);
      PIO_Configure(
         g_APinDescription[MISO_PIN].pPort,
         g_APinDescription[MISO_PIN].ulPinType,
         g_APinDescription[MISO_PIN].ulPin,
         g_APinDescription[MISO_PIN].ulPinConfiguration);

      // set master mode, peripheral select, fault detection
      SPI_Configure(SPI0, ID_SPI0, SPI_MR_MSTR | SPI_MR_MODFDIS | SPI_MR_PS);
      SPI_Enable(SPI0);

      #if MB(ALLIGATOR)
        SET_OUTPUT(DAC0_SYNC);
        #if EXTRUDERS > 1
          SET_OUTPUT(DAC1_SYNC);
          WRITE(DAC1_SYNC, HIGH);
        #endif
        SET_OUTPUT(SPI_EEPROM1_CS);
        SET_OUTPUT(SPI_EEPROM2_CS);
        SET_OUTPUT(SPI_FLASH_CS);
        WRITE(DAC0_SYNC, HIGH);
        WRITE(SPI_EEPROM1_CS, HIGH );
        WRITE(SPI_EEPROM2_CS, HIGH );
        WRITE(SPI_FLASH_CS, HIGH );
        WRITE(SS_PIN, HIGH );
      #endif // MB(ALLIGATOR)

      PIO_Configure(
        g_APinDescription[SPI_PIN].pPort,
        g_APinDescription[SPI_PIN].ulPinType,
        g_APinDescription[SPI_PIN].ulPin,
        g_APinDescription[SPI_PIN].ulPinConfiguration);
      spiInit(1);
      spiInitMaded = true;
    }
  }

  void spiInit(uint8_t spiRate) {
    if(spiInitMaded == false) {
      if(spiRate > 6) spiRate = 1;

      #if MB(ALLIGATOR)
        // Set SPI mode 1, clock, select not active after transfer, with delay between transfers
        SPI_ConfigureNPCS(SPI0, SPI_CHAN_DAC,
                          SPI_CSR_CSAAT | SPI_CSR_SCBR(spiDueDividors[spiRate]) |
                          SPI_CSR_DLYBCT(1));
        // Set SPI mode 0, clock, select not active after transfer, with delay between transfers
        SPI_ConfigureNPCS(SPI0, SPI_CHAN_EEPROM1, SPI_CSR_NCPHA |
                          SPI_CSR_CSAAT | SPI_CSR_SCBR(spiDueDividors[spiRate]) |
                          SPI_CSR_DLYBCT(1));
      #endif//MB(ALLIGATOR)

      // Set SPI mode 0, clock, select not active after transfer, with delay between transfers
      SPI_ConfigureNPCS(SPI0, SPI_CHAN, SPI_CSR_NCPHA |
                        SPI_CSR_CSAAT | SPI_CSR_SCBR(spiDueDividors[spiRate]) |
                        SPI_CSR_DLYBCT(1));
      SPI_Enable(SPI0);
      spiInitMaded = true;
    }
  }

  // Write single byte to SPI
  void spiSend(byte b) {
    // write byte with address and end transmission flag
    SPI0->SPI_TDR = (uint32_t)b | SPI_PCS(SPI_CHAN) | SPI_TDR_LASTXFER;
    // wait for transmit register empty
    while ((SPI0->SPI_SR & SPI_SR_TDRE) == 0);
    // wait for receive register
    while ((SPI0->SPI_SR & SPI_SR_RDRF) == 0);
    // clear status
    SPI0->SPI_RDR;
    //delayMicroseconds(1U);
  }

  void spiSend(const uint8_t* buf, size_t n) {
    if (n == 0) return;
    for (size_t i = 0; i < n - 1; i++) {
      SPI0->SPI_TDR = (uint32_t)buf[i] | SPI_PCS(SPI_CHAN);
      while ((SPI0->SPI_SR & SPI_SR_TDRE) == 0);
      while ((SPI0->SPI_SR & SPI_SR_RDRF) == 0);
      SPI0->SPI_RDR;
      //delayMicroseconds(1U);
    }
    spiSend(buf[n - 1]);
  }

  void spiSend(uint32_t chan, byte b) {
    uint8_t dummy_read = 0;
    // wait for transmit register empty
    while ((SPI0->SPI_SR & SPI_SR_TDRE) == 0);
    // write byte with address and end transmission flag
    SPI0->SPI_TDR = (uint32_t)b | SPI_PCS(chan) | SPI_TDR_LASTXFER;
    // wait for receive register
    while ((SPI0->SPI_SR & SPI_SR_RDRF) == 0);
    // clear status
    while ((SPI0->SPI_SR & SPI_SR_RDRF) == 1)
      dummy_read = SPI0->SPI_RDR;
    UNUSED(dummy_read);
  }

  void spiSend(uint32_t chan, const uint8_t* buf, size_t n) {
    uint8_t dummy_read = 0;
    if (n == 0) return;
    for (int i = 0; i < (int)n - 1; i++) {
      while ((SPI0->SPI_SR & SPI_SR_TDRE) == 0);
      SPI0->SPI_TDR = (uint32_t)buf[i] | SPI_PCS(chan);
      while ((SPI0->SPI_SR & SPI_SR_RDRF) == 0);
      while ((SPI0->SPI_SR & SPI_SR_RDRF) == 1)
        dummy_read = SPI0->SPI_RDR;
      UNUSED(dummy_read);
    }
    spiSend(chan, buf[n - 1]);
  }

  // Read single byte from SPI
  uint8_t spiRec() {
    // write dummy byte with address and end transmission flag
    SPI0->SPI_TDR = 0x000000FF | SPI_PCS(SPI_CHAN) | SPI_TDR_LASTXFER;
    // wait for transmit register empty
    while ((SPI0->SPI_SR & SPI_SR_TDRE) == 0);

    // wait for receive register
    while ((SPI0->SPI_SR & SPI_SR_RDRF) == 0);
    // get byte from receive register
    //delayMicroseconds(1U);
    return SPI0->SPI_RDR;
  }

  uint8_t spiRec(uint32_t chan) {
    uint8_t spirec_tmp;
    // wait for transmit register empty
    while ((SPI0->SPI_SR & SPI_SR_TDRE) == 0);
    while ((SPI0->SPI_SR & SPI_SR_RDRF) == 1)
      spirec_tmp =  SPI0->SPI_RDR;
      UNUSED(spirec_tmp);

    // write dummy byte with address and end transmission flag
    SPI0->SPI_TDR = 0x000000FF | SPI_PCS(chan) | SPI_TDR_LASTXFER;

    // wait for receive register
    while ((SPI0->SPI_SR & SPI_SR_RDRF) == 0);
    // get byte from receive register
    return SPI0->SPI_RDR;
  }

  // Read from SPI into buffer
  void spiRead(uint8_t*buf, uint16_t nbyte) {
    if (nbyte-- == 0) return;

    for (int i = 0; i < nbyte; i++) {
      //while ((SPI0->SPI_SR & SPI_SR_TDRE) == 0);
      SPI0->SPI_TDR = 0x000000FF | SPI_PCS(SPI_CHAN);
      while ((SPI0->SPI_SR & SPI_SR_RDRF) == 0);
      buf[i] = SPI0->SPI_RDR;
      //delayMicroseconds(1U);
    }
    buf[nbyte] = spiRec();
  }

  // Write from buffer to SPI
  void spiSendBlock(uint8_t token, const uint8_t* buf) {
    SPI0->SPI_TDR = (uint32_t)token | SPI_PCS(SPI_CHAN);
    while ((SPI0->SPI_SR & SPI_SR_TDRE) == 0);
    //while ((SPI0->SPI_SR & SPI_SR_RDRF) == 0);
    //SPI0->SPI_RDR;
    for (int i = 0; i < 511; i++) {
      SPI0->SPI_TDR = (uint32_t)buf[i] | SPI_PCS(SPI_CHAN);
      while ((SPI0->SPI_SR & SPI_SR_TDRE) == 0);
      while ((SPI0->SPI_SR & SPI_SR_RDRF) == 0);
      SPI0->SPI_RDR;
      //delayMicroseconds(1U);
    }
    spiSend(buf[511]);
  }
#endif // ENABLED(SOFTWARE_SPI)

#endif // ARDUINO_ARCH_SAM