text: /****************************************************************************
   * arch/z16/src/z16f/z16f_espi.c
   *
   *   Copyright (C) 2014, 2016 Gregory Nutt. All rights reserved.
   *   Authors: Gregory Nutt <gnutt@nuttx.org>
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in
   *    the documentation and/or other materials provided with the
   *    distribution.
   * 3. Neither the name NuttX nor the names of its contributors may be
   *    used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
   * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
   * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   * POSSIBILITY OF SUCH DAMAGE.
   *
   ****************************************************************************/
  
  /****************************************************************************
   * Included Files
   ****************************************************************************/
  
  #include <nuttx/config.h>
  
  #include <stdint.h>
  #include <stdbool.h>
  #include <semaphore.h>
  #include <assert.h>
  #include <errno.h>
  #include <debug.h>
  
  #include <arch/board/board.h>
  #include <nuttx/irq.h>
  #include <nuttx/spi/spi.h>
  
  #include "up_arch.h"
  #include "chip.h"
  
  #ifdef CONFIG_Z16F_ESPI
  
  /****************************************************************************
   * Pre-processor Definitions
   ****************************************************************************/
  /* Debug *******************************************************************/
  /* Check if SPI debug is enabled */
  
  #ifdef CONFIG_DEBUG_SPI
  #  define spierr  llerr
  #  define spiwarn llwarn
  #  define spiinfo llinfo
  #else
  #  define spierr(x...)
  #  define spiwarn(x...)
  #  define spiinfo(x...)
  #endif
  
  /****************************************************************************
   * Private Types
   ****************************************************************************/
  
  /* The overall state of one SPI controller */
  
  struct z16f_spi_s
  {
    struct spi_dev_s spi;        /* Externally visible part of the SPI interface */
    bool initialized;            /* TRUE: Controller has been initialized */
    uint8_t nbits;               /* Width of word in bits (1-8) */
    uint8_t mode;                /* Mode 0,1,2,3 */
    sem_t exclsem;               /* Assures mutually exclusive access to SPI */
    uint32_t frequency;          /* Requested clock frequency */
    uint32_t actual;             /* Actual clock frequency */
  
    /* Debug stuff */
  
  #ifdef CONFIG_Z16F_ESPI_REGDEBUG
     bool wr;                    /* Last was a write */
     uint16_t regval;            /* Last value */
     int ntimes;                 /* Number of times */
     uintptr_t regaddr;          /* Last address */
  #endif
  };
  
  /****************************************************************************
   * Private Function Prototypes
   ****************************************************************************/
  
  /* Helpers */
  
  #ifdef CONFIG_Z16F_ESPI_REGDEBUG
  static bool     spi_checkreg(FAR struct z16f_spi_s *priv, bool wr,
                    uint16_t regval, uintptr_t regaddr);
  static uint8_t  spi_getreg8(FAR struct z16f_spi_s *priv, uintptr_t regaddr);
  static void     spi_putreg8(FAR struct z16f_spi_s *priv, uint8_t regval,
                    uintptr_t regaddr);
  static void     spi_putreg16(FAR struct z16f_spi_s *priv, uint16_t regval,
                    uintptr_t regaddr);
  #else
  # define        spi_getreg8(priv,regaddr)         getreg8(regaddr)
  # define        spi_putreg8(priv,regval,regaddr)  putreg8(regval, regaddr)
  # define        spi_putreg16(priv,regval,regaddr) putreg16(regval, regaddr)
  #endif
  
  #if defined(CONFIG_DEBUG_SPI) && defined(CONFIG_DEBUG_INFO)
  static void     spi_dumpregs(FAR struct z16f_spi_s *priv, const char *msg);
  #else
  # define        spi_dumpregs(priv,msg)
  #endif
  
  static void     spi_flush(FAR struct z16f_spi_s *priv);
  
  /* SPI methods */
  
  static int      spi_lock(FAR struct spi_dev_s *dev, bool lock);
  static uint32_t spi_setfrequency(FAR struct spi_dev_s *dev, uint32_t frequency);
  static void     spi_setmode(FAR struct spi_dev_s *dev, enum spi_mode_e mode);
  static void     spi_setbits(FAR struct spi_dev_s *dev, int nbits);
  static uint16_t spi_send(FAR struct spi_dev_s *dev, uint16_t ch);
  static void     spi_exchange(FAR struct spi_dev_s *dev, FAR const void *txbuffer,
                     FAR void *rxbuffer, size_t nwords);
  #ifndef CONFIG_SPI_EXCHANGE
  static void     spi_sndblock(FAR struct spi_dev_s *dev,
                     FAR const void *buffer, size_t nwords);
  static void     spi_recvblock(FAR struct spi_dev_s *dev, FAR void *buffer,
                     size_t nwords);
  #endif
  
  /****************************************************************************
   * Private Data
   ****************************************************************************/
  
  /* SEPI driver operations */
  
  static const struct spi_ops_s g_epsiops =
  {
    spi_lock,
    z16f_espi_select,
    spi_setfrequency,
    spi_setmode,
    spi_setbits,
  #ifdef CONFIG_SPI_HWFEATURES
    NULL, /* hwfeatures:  Not supported */
  #endif
    z16f_espi_status,
  #ifdef CONFIG_SPI_CMDDATA
    z16f_espi_cmddata,
  #endif
    spi_send,
  #ifdef CONFIG_SPI_EXCHANGE
    spi_exchange,
  #else
    spi_sndblock,
    spi_recvblock,
  #endif
    NULL  /* registercallback: Not implemented */
  };
  
  /* ESPI driver state */
  
  static struct z16f_spi_s g_espi;
  
  /****************************************************************************
   * Public Data
   ****************************************************************************/
  
  /****************************************************************************
   * Private Functions
   ****************************************************************************/
  
  /****************************************************************************
   * Name: spi_checkreg
   *
   * Description:
   *   Check if the current register access is a duplicate of the preceding.
   *
   * Input Parameters:
   *   wr      - true:write false:read
   *   regval  - The value to be written
   *   regaddr - The address of the register to write to
   *
   * Returned Value:
   *   true:  This is the first register access of this type.
   *   flase: This is the same as the preceding register access.
   *
   ****************************************************************************/
  
  #ifdef CONFIG_Z16F_ESPI_REGDEBUG
  static bool spi_checkreg(FAR struct z16f_spi_s *priv, bool wr, uint16_t regval,
                           uintptr_t regaddr)
  {
    if (wr      == priv->wr &&      /* Same kind of access? */
        regval  == priv->regval &&  /* Same value? */
        regaddr == priv->regaddr)   /* Same address? */
      {
        /* Yes, then just keep a count of the number of times we did this. */
  
        priv->ntimes++;
        return false;
      }
    else
      {
        /* Did we do the previous operation more than once? */
  
        if (priv->ntimes > 0)
          {
            /* Yes... show how many times we did it */
  
            syslog(LOG_INFO, "...[Repeats %d times]...\n", priv->ntimes);
          }
  
        /* Save information about the new access */
  
        priv->wr      = wr;
        priv->regval  = regval;
        priv->regaddr = regaddr;
        priv->ntimes  = 0;
      }
  
    /* Return true if this is the first time that we have done this operation */
  
    return true;
  }
  #endif
  
  /****************************************************************************
   * Name: spi_getreg8
   *
   * Description:
   *  Read an SPI register
   *
   ****************************************************************************/
  
  #ifdef CONFIG_Z16F_ESPI_REGDEBUG
  static uint8_t spi_getreg8(FAR struct z16f_spi_s *priv, uintptr_t regaddr)
  {
    uint8_t regval = getreg8(regaddr);
  
    if (spi_checkreg(priv, false, (uint16_t)regval, regaddr))
      {
        syslog(LOG_INFO, "%06x->%02x\n", regaddr, regval);
      }
  
    return regval;
  }
  #endif
  
  /****************************************************************************
   * Name: spi_putreg8
   *
   * Description:
   *  Write a value to an SPI register
   *
   ****************************************************************************/
  
  #ifdef CONFIG_Z16F_ESPI_REGDEBUG
  static void spi_putreg8(FAR struct z16f_spi_s *priv, uint8_t regval,
                          uintptr_t regaddr)
  {
    if (spi_checkreg(priv, true, (uint16_t)regval, regaddr))
      {
        syslog(LOG_INFO, "%06x<-%02x\n", regaddr, regval);
      }
  
    putreg8(regval, regaddr);
  }
  #endif
  
  /****************************************************************************
   * Name: spi_putreg16
   *
   * Description:
   *  Write a value to an SPI register
   *
   ****************************************************************************/
  
  #ifdef CONFIG_Z16F_ESPI_REGDEBUG
  static void spi_putreg16(FAR struct z16f_spi_s *priv, uint16_t regval,
                           uintptr_t regaddr)
  {
    if (spi_checkreg(priv, true, regval, regaddr))
      {
        syslog(LOG_INFO, "%06x<-%04x\n", regaddr, regval);
      }
  
    putreg8(regval, regaddr);
  }
  #endif
  
  /****************************************************************************
   * Name: spi_dumpregs
   *
   * Description:
   *   Dump the contents of all SPI registers
   *
   * Input Parameters:
   *   priv - The SPI controller to dump
   *   msg - Message to print before the register data
   *
   * Returned Value:
   *   None
   *
   ****************************************************************************/
  
  #if defined(CONFIG_DEBUG_SPI) && defined(CONFIG_DEBUG_INFO)
  static void spi_dumpregs(FAR struct z16f_spi_s *priv, FAR const char *msg)
  {
    spiinfo("%s:\n", msg);
    spiinfo("   DCR: %02x  CTL: %02x MODE: %02x STAT: %02x\n",
            getreg8(Z16F_ESPI_DCR),  getreg8(Z16F_ESPI_CTL),
            getreg8(Z16F_ESPI_MODE), getreg8(Z16F_ESPI_STAT));
    spiinfo(" STATE: %02x   BR: %02x %02x\n",
            getreg8(Z16F_ESPI_STATE),  getreg8(Z16F_ESPI_BRH),
            getreg8(Z16F_ESPI_BRL));
  }
  #endif
  
  /****************************************************************************
   * Name: spi_flush
   *
   * Description:
   *   Make sure that there are now dangling SPI transfer in progress
   *
   * Input Parameters:
   *   priv - SPI controller state
   *
   * Returned Value:
   *   None
   *
   ****************************************************************************/
  
  static void spi_flush(FAR struct z16f_spi_s *priv)
  {
    /* Make sure the no transfer is in progress... waiting if necessary */
  
    while ((spi_getreg8(priv, Z16F_ESPI_STAT) & Z16F_ESPI_STAT_TFST) != 0);
  
    /* Then make sure that there is no pending RX data .. reading as
     * discarding as necessary.
     */
  
    while ((spi_getreg8(priv, Z16F_ESPI_STAT) & Z16F_ESPI_STAT_RDRF) != 0)
      {
        (void)spi_getreg8(priv, Z16F_ESPI_DATA);
      }
  }
  
  /****************************************************************************
   * Name: spi_lock
   *
   * Description:
   *   On SPI buses where there are multiple devices, it will be necessary to
   *   lock SPI to have exclusive access to the buses for a sequence of
   *   transfers.  The bus should be locked before the chip is selected. After
   *   locking the SPI bus, the caller should then also call the setfrequency,
   *   setbits, and setmode methods to make sure that the SPI is properly
   *   configured for the device.  If the SPI buss is being shared, then it
   *   may have been left in an incompatible state.
   *
   * Input Parameters:
   *   dev  - Device-specific state data
   *   lock - true: Lock SPI bus, false: unlock SPI bus
   *
   * Returned Value:
   *   None
   *
   ****************************************************************************/
  
  static int spi_lock(FAR struct spi_dev_s *dev, bool lock)
  {
    FAR struct z16f_spi_s *priv = (FAR struct z16f_spi_s *)dev;
  
    spiinfo("lock=%d\n", lock);
    if (lock)
      {
        /* Take the semaphore (perhaps waiting) */
  
        while (sem_wait(&priv->exclsem) != 0)
          {
            /* The only case that an error should occur here is if the wait was awakened
             * by a signal.
             */
  
            ASSERT(errno == EINTR);
          }
      }
    else
      {
        (void)sem_post(&priv->exclsem);
      }
  
    return OK;
  }
  
  /****************************************************************************
   * Name: spi_setfrequency
   *
   * Description:
   *   Set the SPI frequency.
   *
   * Input Parameters:
   *   dev -       Device-specific state data
   *   frequency - The SPI frequency requested
   *
   * Returned Value:
   *   Returns the actual frequency selected
   *
   ****************************************************************************/
  
  static uint32_t spi_setfrequency(FAR struct spi_dev_s *dev, uint32_t frequency)
  {
    FAR struct z16f_spi_s *priv = (FAR struct z16f_spi_s *)dev;
    uint32_t actual;
    uint32_t brg;
  
    spiinfo("frequency=%d\n", frequency);
  
    /* Check if the requested frequency is the same as the frequency selection */
  
    if (priv->frequency == frequency)
      {
        /* We are already at this frequency.  Return the actual. */
  
        return priv->actual;
      }
  
    /* Fbaud = Fsystem / (2 * BRG)
     * BRG   = Fsystem / (2 * Fbaud)
     *
     * Example, Fsystem = 18.432MHz, Fbaud = 9600
     * BRG   = 960
     */
  
    brg = (BOARD_SYSTEM_FREQUENCY >> 1) / frequency;
    if (brg > 0xffff)
      {
        brg = 0xffff;
      }
  
    /* Save the new BRG setting */
  
    spi_putreg16(priv, (uint16_t)brg, Z16F_ESPI_BR);
  
    /* Calculate the new actual frequency */
  
    actual = (BOARD_SYSTEM_FREQUENCY >> 1) / brg;
    spiinfo("BR=%04x actual=%ld\n", (unsigned int)brg, (long)actual);
  
    /* Save the frequency setting */
  
    priv->frequency = frequency;
    priv->actual    = actual;
  
    spiinfo("Frequency %d->%d\n", frequency, actual);
    return actual;
  }
  
  /****************************************************************************
   * Name: spi_setmode
   *
   * Description:
   *   Set the SPI mode. Optional.  See enum spi_mode_e for mode definitions
   *
   * Input Parameters:
   *   dev -  Device-specific state data
   *   mode - The SPI mode requested
   *
   * Returned Value:
   *   none
   *
   ****************************************************************************/
  
  static void spi_setmode(FAR struct spi_dev_s *dev, enum spi_mode_e mode)
  {
    FAR struct z16f_spi_s *priv = (FAR struct z16f_spi_s *)dev;
    uint8_t regval;
  
    spiinfo("mode=%d\n", mode);
  
    /* Has the mode changed? */
  
    if (mode != priv->mode)
      {
        /* Yes... Set the mode appropriately:
         *
         * SPI  CPOL CPHA
         * MODE
         *  0    0    0
         *  1    0    1
         *  2    1    0
         *  3    1    1
         */
  
        regval  = spi_getreg8(priv, Z16F_ESPI_CTL);
        regval &= ~(Z16F_ESPI_CTL_PHASE | Z16F_ESPI_CTL_CLKPOL);
  
        switch (mode)
          {
          case SPIDEV_MODE0: /* CPOL=0; NCPHA=1 */
            break;
  
          case SPIDEV_MODE1: /* CPOL=0; NCPHA=0 */
            regval |= Z16F_ESPI_CTL_PHASE;
            break;
  
          case SPIDEV_MODE2: /* CPOL=1; NCPHA=1 */
            regval |= Z16F_ESPI_CTL_CLKPOL;
            break;
  
          case SPIDEV_MODE3: /* CPOL=1; NCPHA=0 */
            regval |= (Z16F_ESPI_CTL_PHASE | Z16F_ESPI_CTL_CLKPOL);
            break;
  
          default:
            DEBUGASSERT(false);
            return;
          }
  
        spi_putreg8(priv, regval, Z16F_ESPI_CTL);
        spiinfo("ESPI CTL: %02x\n", regval);
  
        /* Save the mode so that subsequent re-configurations will be faster */
  
        priv->mode = mode;
      }
  }
  
  /****************************************************************************
   * Name: spi_setbits
   *
   * Description:
   *   Set the number if bits per word.
   *
   * Input Parameters:
   *   dev -  Device-specific state data
   *   nbits - The number of bits requests
   *
   * Returned Value:
   *   none
   *
   ****************************************************************************/
  
  static void spi_setbits(FAR struct spi_dev_s *dev, int nbits)
  {
    FAR struct z16f_spi_s *priv = (FAR struct z16f_spi_s *)dev;
    uint8_t regval;
  
    spiinfo("nbits=%d\n", nbits);
    DEBUGASSERT(priv && nbits > 0 && nbits <= 8);
  
    /* Has the number of bits changed? */
  
    if (nbits != priv->nbits)
      {
        /* Yes... Set number of bits appropriately */
  
        regval  = spi_getreg8(priv, Z16F_ESPI_MODE);
        regval &= ~Z16F_ESPI_MODE_NUMBITS_MASK;
  
        /* The register value of zero is 8-bit */
  
        if (nbits < 8)
          {
            regval |= ((uint8_t)nbits << Z16F_ESPI_MODE_NUMBITS_SHIFT);
          }
  
        spi_putreg8(priv, regval, Z16F_ESPI_MODE);
        spiinfo("ESPI MODE: %02x\n", regval);
  
        /* Save the selection so the subsequence re-configurations will be faster */
  
        priv->nbits = nbits;
      }
  }
  
  /****************************************************************************
   * Name: spi_send
   *
   * Description:
   *   Exchange one word on SPI
   *
   * Input Parameters:
   *   dev - Device-specific state data
   *   wd  - The word to send.  the size of the data is determined by the
   *         number of bits selected for the SPI interface.
   *
   * Returned Value:
   *   response
   *
   ****************************************************************************/
  
  static uint16_t spi_send(FAR struct spi_dev_s *dev, uint16_t wd)
  {
    uint8_t txbyte;
    uint8_t rxbyte;
  
    /* spi_exchange can do this. Note: right now, this only deals with 8-bit
     * words.  If the SPI interface were configured for words of other sizes,
     * this would fail.
     */
  
    txbyte = (uint8_t)wd;
    rxbyte = (uint8_t)0;
    spi_exchange(dev, &txbyte, &rxbyte, 1);
  
    spiinfo("Sent %02x received %02x\n", txbyte, rxbyte);
    return (uint16_t)rxbyte;
  }
  
  /****************************************************************************
   * Name: spi_exchange
   *
   * Description:
   *   Exchange a block of data from SPI.
   *
   * Input Parameters:
   *   dev      - Device-specific state data
   *   txbuffer - A pointer to the buffer of data to be sent
   *   rxbuffer - A pointer to the buffer in which to receive data
   *   nwords   - the length of data that to be exchanged in units of words.
   *              The wordsize is determined by the number of bits-per-word
   *              selected for the SPI interface.  If nbits <= 8, the data is
   *              packed into uint8_t's; if nbits >8, the data is packed into
   *              uint16_t's
   *
   * Returned Value:
   *   None
   *
   ****************************************************************************/
  
  static void spi_exchange(FAR struct spi_dev_s *dev, FAR const void *txbuffer,
                           FAR void *rxbuffer, size_t nwords)
  {
    FAR struct z16f_spi_s *priv = (struct z16f_spi_s *)dev;
    uint8_t data;
    FAR uint8_t *rxptr = rxbuffer;
    FAR const uint8_t *txptr = txbuffer;
  
    spiinfo("txbuffer=%p rxbuffer=%p nwords=%d\n", txbuffer, rxbuffer, nwords);
  
    /* Make sure that any previous transfer is flushed from the hardware */
  
    spi_flush(priv);
  
    /* Make sure the the TEOF bit is not set (SSV must also be zero) */
  
    spi_putreg8(priv, 0, Z16F_ESPI_CTL);
  
    /* Loop, sending each word in the user-provided data buffer.
     *
     * Note 2: This loop might be made more efficient.  Would logic
     *         like the following improve the throughput?  Or would it
     *         just add the risk of overruns?
     *
     *   Get byte 1;
     *   Send byte 1;  Now word 1 is "in flight"
     *   nwords--;
     *   for ( ; byte > 0; byte--)
     *     {
     *       Get byte N.
     *       Wait for TDRE meaning that byte N-1 has moved to the shift
     *          register.
     *       Disable interrupts to keep the following atomic
     *       Send byte N.  Now both work N-1 and N are "in flight"
     *       Wait for RDRF meaning that byte N-1 is available
     *       Read byte N-1.
     *       Re-enable interrupts.
     *       Save byte N-1.
     *     }
     *   Wait for RDRF meaning that the final byte is available
     *   Read the final byte.
     *   Save the final byte.
     */
  
    for ( ; nwords > 0; nwords--)
      {
        /* Get the data to send (0xff if there is no data source). */
  
        if (txptr)
          {
            data = *txptr++;
          }
        else
          {
            data = 0xff;
          }
  
        /* Do we need to set the TEOF bit in the CTL register too? */
  
        if (nwords == 1)
          {
            spi_putreg8(priv, Z16F_ESPI_DCR_TEOF, Z16F_ESPI_CTL);
          }
  
        /* Wait for any transmit data register to be empty. */
  
        while ((spi_getreg8(priv, Z16F_ESPI_STAT) & Z16F_ESPI_STAT_TDRE) == 0);
  
        /* Write the data to transmitted to the Transmit Data Register (TDR) */
  
        spi_putreg8(priv, data, Z16F_ESPI_DATA);
  
        /* Wait for the read data to be available in the data regsiter */
  
        while ((spi_getreg8(priv, Z16F_ESPI_STAT) & Z16F_ESPI_STAT_RDRF) == 0);
  
        /* Read the received data from the SPI Data Register. */
  
        data = spi_getreg8(priv, Z16F_ESPI_DATA);
        if (rxptr)
          {
            *rxptr++ = (uint8_t)data;
          }
      }
  }
  
  /****************************************************************************
   * Name: spi_sndblock
   *
   * Description:
   *   Send a block of data on SPI
   *
   * Input Parameters:
   *   dev -    Device-specific state data
   *   buffer - A pointer to the buffer of data to be sent
   *   nwords - the length of data to send from the buffer in number of words.
   *            The wordsize is determined by the number of bits-per-word
   *            selected for the SPI interface.  If nbits <= 8, the data is
   *            packed into uint8_t's; if nbits >8, the data is packed into
   *            uint16_t's
   *
   * Returned Value:
   *   None
   *
   ****************************************************************************/
  
  #ifndef CONFIG_SPI_EXCHANGE
  static void spi_sndblock(FAR struct spi_dev_s *dev, FAR const void *buffer,
                           size_t nwords)
  {
    /* spi_exchange can do this. */
  
    spi_exchange(dev, buffer, NULL, nwords);
  }
  #endif
  
  /****************************************************************************
   * Name: spi_recvblock
   *
   * Description:
   *   Revice a block of data from SPI
   *
   * Input Parameters:
   *   dev -    Device-specific state data
   *   buffer - A pointer to the buffer in which to receive data
   *   nwords - the length of data that can be received in the buffer in number
   *            of words.  The wordsize is determined by the number of bits-per-word
   *            selected for the SPI interface.  If nbits <= 8, the data is
   *            packed into uint8_t's; if nbits >8, the data is packed into
   *            uint16_t's
   *
   * Returned Value:
   *   None
   *
   ****************************************************************************/
  
  #ifndef CONFIG_SPI_EXCHANGE
  static void spi_recvblock(FAR struct spi_dev_s *dev, FAR void *buffer,
                            size_t nwords)
  {
    /* spi_exchange can do this. */
  
    spi_exchange(dev, NULL, buffer, nwords);
  }
  #endif
  
  /****************************************************************************
   * Public Functions
   ****************************************************************************/
  
  /****************************************************************************
   * Name: z16_spibus_initialize
   *
   * Description:
   *   Initialize the selected SPI port
   *
   * Input Parameter:
   *   port - Identifies the "logical" SPI port.  Must be zero in this case.
   *
   * Returned Value:
   *   Valid SPI device structure reference on success; a NULL on failure
   *
   ****************************************************************************/
  
  FAR struct spi_dev_s *z16_spibus_initialize(int port)
  {
    FAR struct z16f_spi_s *priv;
    irqstate_t flags;
    uint8_t regval;
  
    spiinfo("port: %d\n", port);
    DEBUGASSERT(port == 0);
  
    /* Check if we have already initialized the ESPI */
  
    priv = &g_espi;
    if (priv->initialized)
      {
        /* Initialize the ESPI state structure */
  
        flags = enter_critical_section();
        priv->spi.ops = &g_epsiops;
        sem_init(&priv->exclsem, 0, 1);
  
        /* Set up the SPI pin configuration (board-specific logic is required to
         * configure and manage all chip selects).
         *
         *   SCK  - PC3, Alternate function 1
         *   MOSI - PC4, Alternate function 1
         *   MISO - PC5, Alternate function 1
         */
  
        regval  = spi_getreg8(priv, Z16F_GPIOC_AFL);
        regval |= 0x38;
        spi_putreg8(priv, regval, Z16F_GPIOC_AFL);
  
        regval  = spi_getreg8(priv, Z16F_GPIOC_AFH);
        regval &= ~0x38;
        spi_putreg8(priv, regval, Z16F_GPIOC_AFH);
  
        /* Initialize the ESPI peripheral.  Master, Mode 0, 8-bits, 400KHz */
  
        spi_putreg8(priv, 0x00, Z16F_ESPI_CTL);    /* Disabled the ESPI */
        spi_putreg8(priv, 0x00, Z16F_ESPI_DCR);    /* Disabled slave select; clear TEOF */
  
        regval = Z16F_ESPI_MODE_SSIO | Z16F_ESPI_MODE_NUMBITS_8BITS | Z16F_ESPI_MODE_SSMD_SPI;
        spi_putreg8(priv, regval, Z16F_ESPI_MODE); /* SPI mode, 8-bit */
  
        regval = Z16F_ESPI_CTL_ESPIEN0 | Z16F_ESPI_CTL_MMEN | Z16F_ESPI_CTL_ESPIEN1;
        spi_putreg8(priv, 0x00, Z16F_ESPI_CTL);    /* TX/RX mode, Master mode */
  
        /* Make sure that we are all in agreement about the configuration and set
         * the BRG for 400KHz operation.
         */
  
        (void)spi_setfrequency(&priv->spi, 400000);
        spi_setmode(&priv->spi, SPIDEV_MODE0);
        spi_setbits(&priv->spi, 8);
  
        /* Now we are initialized */
  
        priv->initialized = true;
        leave_critical_section(flags);
      }
  
    spi_dumpregs(priv, "After initialization");
    return &priv->spi;
  }
  
  #endif /* CONFIG_Z16F_ESPI */
  