nuttx/drivers/spi/spi_transfer.c

/****************************************************************************
 * drivers/spi/spi_transfer.c
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <unistd.h>
#include <assert.h>
#include <errno.h>
#include <debug.h>

#include <nuttx/signal.h>
#include <nuttx/spi/spi.h>
#include <nuttx/spi/spi_transfer.h>

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: spi_transfer
 *
 * Description:
 *   This is a helper function that can be used to encapsulate and manage
 *   a sequence of SPI transfers.  The SPI bus will be locked and the
 *   SPI device selected for the duration of the transfers.
 *
 * Input Parameters:
 *   spi - An instance of the SPI device to use for the transfer
 *   seq - Describes the sequence of transfers.
 *
 * Returned Value:
 *   Zero (OK) on success; a negated errno value on failure.
 *
 ****************************************************************************/

int spi_transfer(FAR struct spi_dev_s *spi, FAR struct spi_sequence_s *seq)
{
  FAR struct spi_trans_s *trans;
  int ret = OK;
  int i;

  DEBUGASSERT(spi != NULL && seq != NULL && seq->trans != NULL);

  /* Get exclusive access to the SPI bus */

  SPI_LOCK(spi, true);

  /* Establish the fixed SPI attributes for all transfers in the sequence */

  SPI_SETFREQUENCY(spi, seq->frequency);

#ifdef CONFIG_SPI_DELAY_CONTROL
  ret = SPI_SETDELAY(spi, seq->a, seq->b, seq->c, seq->i);
  if (ret < 0)
    {
      spierr("ERROR: SPI_SETDELAY failed: %d\n", ret);
      SPI_LOCK(spi, false);
      return ret;
    }
#endif

  SPI_SETMODE(spi, (enum spi_mode_e)seq->mode);
  SPI_SETBITS(spi, seq->nbits);

  /* Select the SPI device in preparation for the transfer.
   * REVISIT: This is redundant.
   */

  SPI_SELECT(spi, seq->dev, true);

  /* Then perform each transfer is the sequence */

  for (i = 0, trans = seq->trans; i < (int)seq->ntrans; i++, trans++)
    {
      /* Establish the fixed SPI attributes for unique to this transaction */

#ifdef CONFIG_SPI_HWFEATURES
      ret = SPI_HWFEATURES(spi, trans->hwfeat);
      if (ret < 0)
        {
          spierr("ERROR: SPI_HWFEATURES failed: %d\n", ret);
          break;
        }
#endif

#ifdef CONFIG_SPI_CMDDATA
      ret = SPI_CMDDATA(spi, seq->dev, trans->cmd);
      if (ret < 0)
        {
          spierr("ERROR: SPI_CMDDATA failed: %d\n", ret);
          break;
        }
#endif

      /* [Re-]select the SPI device in preparation for the transfer */

      SPI_SELECT(spi, seq->dev, true);

      /* Perform the transfer */

      SPI_EXCHANGE(spi, trans->txbuffer, trans->rxbuffer, trans->nwords);

      /* Possibly de-select the SPI device after the transfer */

      if (trans->deselect)
        {
          SPI_SELECT(spi, seq->dev, false);
        }

      /* Perform any requested inter-transfer delay */

      if (trans->delay > 0)
        {
          nxsig_usleep(trans->delay);
        }
    }

  SPI_SELECT(spi, seq->dev, false);
  SPI_LOCK(spi, false);
  return ret;
}