emlib/src/em_dma.c

/***************************************************************************//**
 * @file
 * @brief Direct memory access (DMA) module peripheral API
 *******************************************************************************
 * # License
 * <b>Copyright 2018 Silicon Laboratories Inc. www.silabs.com</b>
 *******************************************************************************
 *
 * SPDX-License-Identifier: Zlib
 *
 * The licensor of this software is Silicon Laboratories Inc.
 *
 * This software is provided 'as-is', without any express or implied
 * warranty. In no event will the authors be held liable for any damages
 * arising from the use of this software.
 *
 * Permission is granted to anyone to use this software for any purpose,
 * including commercial applications, and to alter it and redistribute it
 * freely, subject to the following restrictions:
 *
 * 1. The origin of this software must not be misrepresented; you must not
 *    claim that you wrote the original software. If you use this software
 *    in a product, an acknowledgment in the product documentation would be
 *    appreciated but is not required.
 * 2. Altered source versions must be plainly marked as such, and must not be
 *    misrepresented as being the original software.
 * 3. This notice may not be removed or altered from any source distribution.
 *
 ******************************************************************************/

#include "em_dma.h"
#if defined(DMA_PRESENT)

#include "em_cmu.h"
#include "sl_assert.h"
#include "em_bus.h"

/***************************************************************************//**
 * @addtogroup dma DMA - Direct Memory Access
 * @brief Direct Memory Access (DMA) Peripheral API
 * @details
 *  DMA access functions provide basic support for the following
 *  types of DMA cycles:
 *
 *  @li @b Basic, used for transferring data between memory and peripherals.
 *  @li @b Auto-request, used for transferring data between memory locations.
 *  @li @b Ping-pong, used for for continuous transfer of data between memory
 *    and peripherals, automatically toggling between primary and alternate
 *    descriptors.
 *  @li @b Memory @b scatter-gather, used for transferring a number of buffers
 *    between memory locations.
 *  @li @b Peripheral @b scatter-gather, used for transferring a number of
 *    buffers between memory and peripherals.
 *
 *  A basic understanding of the DMA controller is assumed. See
 *  the reference manual for more details.
 *
 *  The term 'descriptor' is synonymous to the 'channel control data
 *  structure' term.
 *
 *  To use the DMA controller, the initialization function must have
 *  been executed once (normally during the system initialization):
 * @verbatim
 * DMA_Init();
 * @endverbatim
 *
 *  Normally, a DMA channel is configured:
 * @verbatim
 * DMA_CfgChannel();
 * @endverbatim
 *
 *  The channel configuration only has to be done once if reusing the channel
 *  for the same purpose later.
 *
 *  To set up a DMA cycle, the primary and/or alternate descriptor
 *  has to be set up as indicated below.
 *
 *  For basic or auto-request cycles, use once on either primary or alternate
 *  descriptor:
 * @verbatim
 * DMA_CfgDescr();
 * @endverbatim
 *
 * For ping-pong cycles, configure both primary or alternate descriptors:
 * @verbatim
 * DMA_CfgDescr(); // Primary descriptor config
 * DMA_CfgDescr(); // Alternate descriptor config
 * @endverbatim
 *
 * For scatter-gather cycles, program the alternate descriptor array:
 * @verbatim
 * // 'n' is the number of scattered buffers
 * // 'descr' points to the start of the alternate descriptor array
 *
 * // Fill in 'cfg'
 * DMA_CfgDescrScatterGather(descr, 0, cfg);
 * // Fill in 'cfg'
 * DMA_CfgDescrScatterGather(descr, 1, cfg);
 * :
 * // Fill in 'cfg'
 * DMA_CfgDescrScatterGather(descr, n - 1, cfg);
 * @endverbatim
 *
 * In many cases, the descriptor configuration only has to be done once if
 * re-using the channel for the same type of DMA cycles later.
 *
 * To activate the DMA cycle, use the respective DMA_Activate...()
 * function.
 *
 * For ping-pong DMA cycles, use DMA_RefreshPingPong() from the callback to
 * prepare the completed descriptor for reuse. Notice that the refresh must
 * be done prior to the other active descriptor completes, otherwise the
 * ping-pong DMA cycle will halt.
 * @{
 ******************************************************************************/

/*******************************************************************************
 **************************   LOCAL FUNCTIONS   ********************************
 ******************************************************************************/

/** @cond DO_NOT_INCLUDE_WITH_DOXYGEN */

/***************************************************************************//**
 * @brief
 *   Prepare the descriptor for the DMA cycle.
 *
 * @details
 *   This function prepares the last parts of the configuration required to start a
 *   DMA cycle. Since the DMA controller itself modifies some parts of the
 *   descriptor during use, those parts need to be refreshed if reusing a
 *   descriptor configuration.
 *
 * @note
 *   If using this function on a descriptor already activated and in use by the
 *   DMA controller, the behavior is undefined.
 *
 * @param[in] channel
 *   The DMA channel to prepare for the DMA cycle.
 *
 * @param[in] cycleCtrl
 *   The DMA cycle type to prepare for.
 *
 * @param[in] primary
 *   @li true - prepare the primary descriptor
 *   @li false - prepare an alternate descriptor
 *
 * @param[in] useBurst
 *   The burst feature is only used on peripherals supporting DMA bursts.
 *   Bursts must not be used if the total length (as given by nMinus1) is
 *   less than the arbitration rate configured for the descriptor.
 *   See the reference manual for more details on burst usage.
 *
 * @param[in] dst
 *   An address to a start location to transfer data to. If NULL, leave setting in
 *   descriptor as is.
 *
 * @param[in] src
 *   An address to a start location to transfer data from. If NULL, leave setting in
 *   descriptor as is.
 *
 * @param[in] nMinus1
 *   A number of elements (minus 1) to transfer (<= 1023).
 ******************************************************************************/
static void DMA_Prepare(unsigned int channel,
                        DMA_CycleCtrl_TypeDef cycleCtrl,
                        bool primary,
                        bool useBurst,
                        void *dst,
                        const void *src,
                        unsigned int nMinus1)
{
  DMA_DESCRIPTOR_TypeDef *descr;
  DMA_DESCRIPTOR_TypeDef *primDescr;
  DMA_CB_TypeDef         *cb;
  uint32_t               inc;
  uint32_t               chBit;
  uint32_t               tmp;

  primDescr = ((DMA_DESCRIPTOR_TypeDef *)(DMA->CTRLBASE)) + channel;

  /* Find a descriptor to configure. */
  if (primary) {
    descr = primDescr;
  } else {
    descr = ((DMA_DESCRIPTOR_TypeDef *)(DMA->ALTCTRLBASE)) + channel;
  }

  /* If callback is defined, update information on whether the callback is issued */
  /* for primary or alternate descriptor. This is mainly needed for ping-pong */
  /* cycles. */
  cb = (DMA_CB_TypeDef *)(primDescr->USER);
  if (cb) {
    cb->primary = (uint8_t)primary;
  }

  if (src) {
    inc = (descr->CTRL & _DMA_CTRL_SRC_INC_MASK) >> _DMA_CTRL_SRC_INC_SHIFT;
    if (inc == _DMA_CTRL_SRC_INC_NONE) {
      descr->SRCEND = (volatile void*)src;
    } else {
      descr->SRCEND = (void *)((uint32_t)src + (nMinus1 << inc));
    }
  }

  if (dst) {
    inc = (descr->CTRL & _DMA_CTRL_DST_INC_MASK) >> _DMA_CTRL_DST_INC_SHIFT;
    if (inc == _DMA_CTRL_DST_INC_NONE) {
      descr->DSTEND = dst;
    } else {
      descr->DSTEND = (void *)((uint32_t)dst + (nMinus1 << inc));
    }
  }

  chBit = 1 << channel;
  if (useBurst) {
    DMA->CHUSEBURSTS = chBit;
  } else {
    DMA->CHUSEBURSTC = chBit;
  }

  if (primary) {
    DMA->CHALTC = chBit;
  } else {
    DMA->CHALTS = chBit;
  }

  /* Set the cycle control. */
  tmp  = descr->CTRL & ~(_DMA_CTRL_CYCLE_CTRL_MASK | _DMA_CTRL_N_MINUS_1_MASK);
  tmp |= nMinus1 << _DMA_CTRL_N_MINUS_1_SHIFT;
  tmp |= (uint32_t)cycleCtrl << _DMA_CTRL_CYCLE_CTRL_SHIFT;
  descr->CTRL = tmp;
}

/** @endcond */

/*******************************************************************************
 ************************   INTERRUPT FUNCTIONS   ******************************
 ******************************************************************************/

#ifndef EXCLUDE_DEFAULT_DMA_IRQ_HANDLER

/***************************************************************************//**
 * @brief
 *   Interrupt handler for the DMA cycle completion handling.
 *
 * @details
 *   Clears any pending flags and calls registered callback (if any).
 *
 *   If using the default interrupt vector table setup provided, this function
 *   is automatically placed in the IRQ table due to weak linking. If taking
 *   control over the interrupt vector table in some other way, this interrupt
 *   handler must be installed to support callback actions.
 *
 *   For the user to implement a custom IRQ handler or run without
 *   a DMA IRQ handler, define EXCLUDE_DEFAULT_DMA_IRQ_HANDLER
 *   with a \#define statement or with the compiler option -D.
 *
 ******************************************************************************/
void DMA_IRQHandler(void)
{
  int                    channel;
  DMA_CB_TypeDef         *cb;
  uint32_t               pending;
  uint32_t               pendingPrio;
  uint32_t               prio;
  uint32_t               primaryCpy;
  int                    i;

  /* Get all pending and enabled interrupts. */
  pending  = DMA->IF;
  pending &= DMA->IEN;

  /* Assert on bus error. */
  EFM_ASSERT(!(pending & DMA_IF_ERR));

  /* Process all pending channel interrupts. First process channels */
  /* defined with high priority, then those with default priority. */
  prio        = DMA->CHPRIS;
  pendingPrio = pending & prio;
  for (i = 0; i < 2; i++) {
    channel = 0;
    /* Process pending interrupts within high/default priority group */
    /* honoring the priority within the group. */
    while (pendingPrio) {
      if (pendingPrio & 1) {
        DMA_DESCRIPTOR_TypeDef *descr = (DMA_DESCRIPTOR_TypeDef *)(DMA->CTRLBASE);
        uint32_t chmask = 1 << channel;

        /* Clear a pending interrupt prior to invoking the callback, in case it */
        /* sets up another DMA cycle. */
        DMA->IFC = chmask;

        /* Normally, no point in enabling interrupt without the callback, but */
        /* check if the callback is defined anyway. Callback information is always */
        /* located in the primary descriptor. */
        cb = (DMA_CB_TypeDef *)(descr[channel].USER);
        if (cb) {
          /* Toggle next-descriptor indicator always prior to invoking */
          /* callback (in case callback reconfigures something). */
          primaryCpy   = cb->primary;
          cb->primary ^= 1;
          if (cb->cbFunc) {
            cb->cbFunc(channel, (bool)primaryCpy, cb->userPtr);
          }
        }
      }

      pendingPrio >>= 1;
      channel++;
    }

    /* On second iteration, process default priority channels. */
    pendingPrio = pending & ~prio;
  }
}

#endif /* EXCLUDE_DEFAULT_DMA_IRQ_HANDLER */

/*******************************************************************************
 **************************   GLOBAL FUNCTIONS   *******************************
 ******************************************************************************/

/***************************************************************************//**
 * @brief
 *   Activate the DMA auto-request cycle (used for memory-memory transfers).
 *
 * @details
 *   Prior to activating the DMA cycle, the channel and descriptor to be used
 *   must have been properly configured.
 *
 * @note
 *   If using this function on a channel already activated and in use by the
 *   DMA controller, the behavior is undefined.
 *
 * @param[in] channel
 *   The DMA channel to activate the DMA cycle for.
 *
 * @param[in] primary
 *   @li true - activate using the primary descriptor
 *   @li false - activate using an alternate descriptor
 *
 * @param[in] dst
 *   An ddress to a start location to transfer data to. If NULL, leave setting in
 *   descriptor as is from a previous activation.
 *
 * @param[in] src
 *   An address to a start location to transfer data from. If NULL, leave setting in
 *   descriptor as is from a previous activation.
 *
 * @param[in] nMinus1
 *   A number of DMA transfer elements (minus 1) to transfer (<= 1023). The
 *   size of the DMA transfer element (1, 2 or 4 bytes) is configured with
 *   DMA_CfgDescr().
 ******************************************************************************/
void DMA_ActivateAuto(unsigned int channel,
                      bool primary,
                      void *dst,
                      const void *src,
                      unsigned int nMinus1)
{
  uint32_t chBit;

  EFM_ASSERT(channel < DMA_CHAN_COUNT);
  EFM_ASSERT(nMinus1 <= (_DMA_CTRL_N_MINUS_1_MASK >> _DMA_CTRL_N_MINUS_1_SHIFT));

  DMA_Prepare(channel,
              dmaCycleCtrlAuto,
              primary,
              false,
              dst,
              src,
              nMinus1);

  chBit        = 1 << channel;
  DMA->CHENS   = chBit; /* Enable the channel. */
  DMA->CHSWREQ = chBit; /* Activate with the software request. */
}

/***************************************************************************//**
 * @brief
 *   Activate the DMA basic cycle (used for memory-peripheral transfers).
 *
 * @details
 *   Prior to activating the DMA cycle, the channel and descriptor to be used
 *   must have been properly configured.
 *
 * @note
 *   If using this function on a channel already activated and in use by the
 *   DMA controller, the behavior is undefined.
 *
 * @param[in] channel
 *   The DMA channel to activate the DMA cycle for.
 *
 * @param[in] primary
 *   @li true - activate using the primary descriptor
 *   @li false - activate using an alternate descriptor
 *
 * @param[in] useBurst
 *   The burst feature is only used on peripherals supporting DMA bursts.
 *   Bursts must not be used if the total length (as given by nMinus1) is
 *   less than the arbitration rate configured for the descriptor.
 *   See the reference manual for more details on burst usage.
 *
 * @param[in] dst
 *   An address to a start location to transfer data to. If NULL, leave setting in
 *   descriptor as is from a previous activation.
 *
 * @param[in] src
 *   An address to a start location to transfer data from. If NULL, leave setting in
 *   descriptor as is from a previous activation.
 *
 * @param[in] nMinus1
 *   A number of DMA transfer elements (minus 1) to transfer (<= 1023). The
 *   size of the DMA transfer element (1, 2 or 4 bytes) is configured with
 *   DMA_CfgDescr().
 ******************************************************************************/
void DMA_ActivateBasic(unsigned int channel,
                       bool primary,
                       bool useBurst,
                       void *dst,
                       const void *src,
                       unsigned int nMinus1)
{
  EFM_ASSERT(channel < DMA_CHAN_COUNT);
  EFM_ASSERT(nMinus1 <= (_DMA_CTRL_N_MINUS_1_MASK >> _DMA_CTRL_N_MINUS_1_SHIFT));

  DMA_Prepare(channel,
              dmaCycleCtrlBasic,
              primary,
              useBurst,
              dst,
              src,
              nMinus1);

  /* Enable channel, request signal is provided by the peripheral device. */
  DMA->CHENS = 1 << channel;
}

/***************************************************************************//**
 * @brief
 *   Activate a DMA ping-pong cycle (used for memory-peripheral transfers).
 *
 * @details
 *   Prior to activating the DMA cycle, the channel and both descriptors must
 *   have been properly configured. The primary descriptor is always the first
 *   descriptor to be used by the DMA controller.
 *
 * @note
 *   If using this function on a channel already activated and in use by the
 *   DMA controller, the behavior is undefined.
 *
 * @param[in] channel
 *   The DMA channel to activate DMA cycle for.
 *
 * @param[in] useBurst
 *   The burst feature is only used on peripherals supporting DMA bursts.
 *   Bursts must not be used if the total length (as given by nMinus1) is
 *   less than the arbitration rate configured for the descriptors.
 *   See the reference manual for more details on burst usage. Notice
 *   that this setting is used for both the primary and alternate descriptors.
 *
 * @param[in] primDst
 *   An address to a start location to transfer data to, for the primary descriptor.
 *   If NULL, leave setting in descriptor as is from a previous activation.
 *
 * @param[in] primSrc
 *   An address to a start location to transfer data from, for the primary descriptor.
 *   If NULL, leave setting in the descriptor as is from a previous activation.
 *
 * @param[in] primNMinus1
 *   A number of DMA transfer elements (minus 1) to transfer (<= 1023), for
 *   primary descriptor. The size of the DMA transfer element (1, 2 or 4 bytes)
 *   is configured with DMA_CfgDescr().
 *
 * @param[in] altDst
 *   An address to a start location to transfer data to, for an alternate descriptor.
 *   If NULL, leave setting in descriptor as is from a previous activation.
 *
 * @param[in] altSrc
 *   An address to a start location to transfer data from, for an alternate descriptor.
 *   If NULL, leave setting in descriptor as is from a previous activation.
 *
 * @param[in] altNMinus1
 *   A number of DMA transfer elements (minus 1) to transfer (<= 1023), for
 *   an alternate descriptor. The size of the DMA transfer element (1, 2 or 4 bytes)
 *   is configured with DMA_CfgDescr().
 ******************************************************************************/
void DMA_ActivatePingPong(unsigned int channel,
                          bool useBurst,
                          void *primDst,
                          const void *primSrc,
                          unsigned int primNMinus1,
                          void *altDst,
                          const void *altSrc,
                          unsigned int altNMinus1)
{
  EFM_ASSERT(channel < DMA_CHAN_COUNT);
  EFM_ASSERT(primNMinus1 <= (_DMA_CTRL_N_MINUS_1_MASK >> _DMA_CTRL_N_MINUS_1_SHIFT));
  EFM_ASSERT(altNMinus1 <= (_DMA_CTRL_N_MINUS_1_MASK >> _DMA_CTRL_N_MINUS_1_SHIFT));

  /* Prepare alternate descriptor first */
  DMA_Prepare(channel,
              dmaCycleCtrlPingPong,
              false,
              useBurst,
              altDst,
              altSrc,
              altNMinus1);

  /* Prepare the primary descriptor last to start a cycle using it. */
  DMA_Prepare(channel,
              dmaCycleCtrlPingPong,
              true,
              useBurst,
              primDst,
              primSrc,
              primNMinus1);

  /* Enable the channel, the request signal is provided by the peripheral device. */
  DMA->CHENS = 1 << channel;
}

/***************************************************************************//**
 * @brief
 *   Activate the DMA scatter-gather cycle (used for either memory-peripheral
 *   or memory-memory transfers).
 *
 * @details
 *   Prior to activating the DMA cycle, the array with alternate descriptors
 *   must have been properly configured. This function can be reused without
 *   reconfiguring the alternate descriptors, as long as @p count is the same.
 *
 * @note
 *   If using this function on a channel already activated and in use by the
 *   DMA controller, the behavior is undefined.
 *
 * @param[in] channel
 *   The DMA channel to activate DMA cycle for.
 *
 * @param[in] useBurst
 *   The burst feature is only used on peripherals supporting DMA bursts
 *   (this parameter is ignored for memory scatter-gather cycles).
 *   This parameter determines if bursts should be enabled during DMA transfers
 *   using the alternate descriptors. Bursts must not be used if the total
 *   length (as given by nMinus1 for the alternate descriptor) is
 *   less than the arbitration rate configured for the descriptor.
 *   See the reference manual for more details on burst usage.
 *
 * @param[in,out] altDescr
 *   A pointer to a start of an array with prepared alternate descriptors. The last
 *   descriptor will have its cycle control type reprogrammed to a basic type.
 *
 * @param[in] count
 *   A number of alternate descriptors in @p altDescr array. The maximum number of
 *   alternate descriptors is 256.
 ******************************************************************************/
void DMA_ActivateScatterGather(unsigned int channel,
                               bool useBurst,
                               DMA_DESCRIPTOR_TypeDef *altDescr,
                               unsigned int count)
{
  DMA_DESCRIPTOR_TypeDef *descr;
  DMA_CB_TypeDef         *cb;
  uint32_t               cycleCtrl;
  uint32_t               chBit;

  EFM_ASSERT(channel < DMA_CHAN_COUNT);
  EFM_ASSERT(altDescr);
  EFM_ASSERT(count && (count <= 256));

  /* Configure the primary descriptor properly to */
  /* transfer one complete alternate descriptor from the alternate */
  /* descriptor table into the actual alternate descriptor. */
  descr = (DMA_DESCRIPTOR_TypeDef *)(DMA->CTRLBASE) + channel;

  /* Set the source end address to point to the alternate descriptor array. */
  descr->SRCEND = (uint32_t *)altDescr + (count * 4) - 1;

  /* The destination end address in the primary descriptor MUST point */
  /* to the corresponding alternate descriptor in scatter-gather mode. */
  descr->DSTEND = (uint32_t *)((DMA_DESCRIPTOR_TypeDef *)(DMA->ALTCTRLBASE)
                               + channel + 1) - 1;

  /* The user field of the descriptor is used for the callback configuration */
  /* and is already configured when the channel is configured. Do not modify it. */

  /* Determine from alternate configuration whether this is a memory or a */
  /* peripheral scatter-gather by looking at the first alternate descriptor. */
  cycleCtrl  = altDescr->CTRL & _DMA_CTRL_CYCLE_CTRL_MASK;
  cycleCtrl &= ~(1 << _DMA_CTRL_CYCLE_CTRL_SHIFT);

  EFM_ASSERT((cycleCtrl == dmaCycleCtrlMemScatterGather)
             || (cycleCtrl == dmaCycleCtrlPerScatterGather));

  /* Set the last alternate descriptor to basic or auto-request a cycle type in */
  /* order to have dma_done signal asserted when complete. Otherwise, an interrupt */
  /* will not be triggered when done. */
  altDescr[count - 1].CTRL &= ~_DMA_CTRL_CYCLE_CTRL_MASK;
  if (cycleCtrl == dmaCycleCtrlMemScatterGather) {
    altDescr[count - 1].CTRL |= (uint32_t)dmaCycleCtrlAuto
                                << _DMA_CTRL_CYCLE_CTRL_SHIFT;
  } else {
    altDescr[count - 1].CTRL |= (uint32_t)dmaCycleCtrlBasic
                                << _DMA_CTRL_CYCLE_CTRL_SHIFT;
  }

  /* If the callback is defined, update the information on whether the callback is issued for */
  /* primary or alternate descriptors. Not really useful for scatter-gather */
  /* but there for consistency. Always set to alternate, since that is the last */
  /* descriptor used. */
  cb = (DMA_CB_TypeDef *)(descr->USER);
  if (cb) {
    cb->primary = false;
  }

  /* Configure the primary descriptor control word. */
  descr->CTRL = ((uint32_t)dmaDataInc4 << _DMA_CTRL_DST_INC_SHIFT)
                | ((uint32_t)dmaDataSize4 << _DMA_CTRL_DST_SIZE_SHIFT)
                | ((uint32_t)dmaDataInc4 << _DMA_CTRL_SRC_INC_SHIFT)
                | ((uint32_t)dmaDataSize4 << _DMA_CTRL_SRC_SIZE_SHIFT)
                /* Use the same protection scheme as for alternate descriptors. */
                | (altDescr->CTRL & _DMA_CTRL_SRC_PROT_CTRL_MASK)
                | ((uint32_t)dmaArbitrate4 << _DMA_CTRL_R_POWER_SHIFT)
                | (((count * 4) - 1) << _DMA_CTRL_N_MINUS_1_SHIFT)
                | (((uint32_t)useBurst & 1) << _DMA_CTRL_NEXT_USEBURST_SHIFT)
                | cycleCtrl;

  chBit = 1 << channel;

  /* Start with the primary descriptor. */
  DMA->CHALTC = chBit;

  /* Enable the channel. */
  DMA->CHENS = chBit;

  /* Send a request if memory scatter-gather. Otherwise, the request signal is */
  /* provided by the peripheral. */
  if (cycleCtrl == dmaCycleCtrlMemScatterGather) {
    DMA->CHSWREQ = chBit;
  }
}

/***************************************************************************//**
 * @brief
 *   Configure a DMA channel.
 *
 * @details
 *   Configure miscellaneous issues for a DMA channel. This function is typically
 *   used once to set up a channel for a certain type of use.
 *
 * @note
 *   If using this function on a channel already in use by the DMA controller,
 *   the behavior is undefined.
 *
 * @param[in] channel
 *   The DMA channel to configure.
 *
 * @param[in] cfg
 *   The configuration to use.
 ******************************************************************************/
void DMA_CfgChannel(unsigned int channel, DMA_CfgChannel_TypeDef *cfg)
{
  DMA_DESCRIPTOR_TypeDef *descr;

  EFM_ASSERT(channel < DMA_CHAN_COUNT);
  EFM_ASSERT(cfg);

  /* Always keep callback configuration reference in the primary descriptor. */
  descr               = (DMA_DESCRIPTOR_TypeDef *)(DMA->CTRLBASE);
  descr[channel].USER = (uint32_t)(cfg->cb);

  /* Set to a specified priority for a channel. */
  if (cfg->highPri) {
    DMA->CHPRIS = 1 << channel;
  } else {
    DMA->CHPRIC = 1 << channel;
  }

  /* Set the DMA signal source select. */
  DMA->CH[channel].CTRL = cfg->select;

  /* Enable/disable an interrupt as specified. */
  if (cfg->enableInt) {
    DMA->IFC = (1 << channel);
    BUS_RegBitWrite(&(DMA->IEN), channel, 1);
  } else {
    BUS_RegBitWrite(&(DMA->IEN), channel, 0);
  }
}

/***************************************************************************//**
 * @brief
 *   Configure the DMA descriptor for auto-request, basic, or ping-pong DMA cycles.
 *
 * @details
 *   This function is used to configure a descriptor for the following
 *   DMA cycle types:
 *
 *   @li auto-request - used for a memory/memory transfer
 *   @li basic - used for a peripheral/memory transfer
 *   @li ping-pong - used for a ping-pong-based peripheral/memory transfer
 *     style providing time to refresh one descriptor while the other is
 *     in use.
 *
 *   The DMA cycle is not activated. See DMA_ActivateAuto(),
 *   DMA_ActivateBasic(), or DMA_ActivatePingPong() to activate the DMA cycle.
 *   In many cases, the configuration only has to be done once, and all
 *   subsequent cycles may be activated with the activate function.
 *
 *   For ping-pong DMA cycles, this function must be used both on the primary
 *   and the alternate descriptor prior to activating the DMA cycle.
 *
 *   Notice that the DMA channel must also be configured. See DMA_CfgChannel().
 *
 * @note
 *   If using this function on a descriptor already activated and in use by
 *   the DMA controller, the behavior is undefined.
 *
 * @param[in] channel
 *   The DMA channel to configure for.
 *
 * @param[in] primary
 *   @li true - configure the primary descriptor
 *   @li false - configure an alternate descriptor
 *
 * @param[in] cfg
 *   The configuration to use.
 ******************************************************************************/
void DMA_CfgDescr(unsigned int channel,
                  bool primary,
                  DMA_CfgDescr_TypeDef *cfg)
{
  DMA_DESCRIPTOR_TypeDef *descr;

  EFM_ASSERT(channel < DMA_CHAN_COUNT);
  EFM_ASSERT(cfg);

  /* Find a descriptor to configure. */
  if (primary) {
    descr = (DMA_DESCRIPTOR_TypeDef *)DMA->CTRLBASE;
  } else {
    descr = (DMA_DESCRIPTOR_TypeDef *)DMA->ALTCTRLBASE;
  }
  descr += channel;

  /* Prepare the descriptor. */
  /* The source/destination end addresses set when started. */
  descr->CTRL = (cfg->dstInc << _DMA_CTRL_DST_INC_SHIFT)
                | (cfg->size << _DMA_CTRL_DST_SIZE_SHIFT)
                | (cfg->srcInc << _DMA_CTRL_SRC_INC_SHIFT)
                | (cfg->size << _DMA_CTRL_SRC_SIZE_SHIFT)
                | ((uint32_t)(cfg->hprot) << _DMA_CTRL_SRC_PROT_CTRL_SHIFT)
                | (cfg->arbRate << _DMA_CTRL_R_POWER_SHIFT)
                | (0 << _DMA_CTRL_N_MINUS_1_SHIFT)     /* Set when activated. */
                | (0 << _DMA_CTRL_NEXT_USEBURST_SHIFT) /* Set when activated. */
                | DMA_CTRL_CYCLE_CTRL_INVALID;         /* Set when activated. */
}

#if defined(_DMA_LOOP0_MASK) && defined(_DMA_LOOP1_MASK)
/***************************************************************************//**
 * @brief Configure the DMA channel for Loop mode or 2D transfer.
 *
 * @details
 *   For 2D transfer, set cfg->enable to "false" and only configure nMinus1
 *   to the same width as the channel descriptor.
 *
 * @param[in] channel
 *   The DMA channel to configure for.
 *
 * @param[in] cfg
 *   The configuration to use.
 ******************************************************************************/
void DMA_CfgLoop(unsigned int channel, DMA_CfgLoop_TypeDef *cfg)
{
  EFM_ASSERT(channel <= 1);
  EFM_ASSERT(cfg->nMinus1 <= 1023);

  /* Configure the LOOP setting. */
  switch ( channel ) {
    case 0:
      DMA->LOOP0 = (cfg->enable    << _DMA_LOOP0_EN_SHIFT)
                   | (cfg->nMinus1 << _DMA_LOOP0_WIDTH_SHIFT);
      break;
    case 1:
      DMA->LOOP1 = (cfg->enable    << _DMA_LOOP1_EN_SHIFT)
                   | (cfg->nMinus1 << _DMA_LOOP1_WIDTH_SHIFT);
      break;
  }
}
#endif

#if defined(_DMA_RECT0_MASK)
/***************************************************************************//**
 * @brief Configure the DMA channel 2D transfer properties.
 *
 * @param[in] channel
 *   The DMA channel to configure for.
 *
 * @param[in] cfg
 *   The configuration to use.
 ******************************************************************************/
void DMA_CfgRect(unsigned int channel, DMA_CfgRect_TypeDef *cfg)
{
  (void)channel;                            /* Unused parameter */

  EFM_ASSERT(channel == 0);
  EFM_ASSERT(cfg->dstStride <= 2047);
  EFM_ASSERT(cfg->srcStride <= 2047);
  EFM_ASSERT(cfg->height <= 1023);

  /* Configure the rectangular/2D copy. */
  DMA->RECT0 = (cfg->dstStride   << _DMA_RECT0_DSTSTRIDE_SHIFT)
               | (cfg->srcStride << _DMA_RECT0_SRCSTRIDE_SHIFT)
               | (cfg->height    << _DMA_RECT0_HEIGHT_SHIFT);
}
#endif

/***************************************************************************//**
 * @brief
 *   Configure an alternate DMA descriptor for use with scatter-gather DMA
 *   cycles.
 *
 * @details
 *   In scatter-gather mode, the alternate descriptors are located in one
 *   contiguous memory area. Each of the alternate descriptors must be fully
 *   configured prior to starting the scatter-gather DMA cycle.
 *
 *   The DMA cycle is not activated by this function. See
 *   DMA_ActivateScatterGather() to activate the DMA cycle. In some cases, the
 *   alternate configuration only has to be done once and all subsequent
 *   transfers may be activated with the activate function.
 *
 *   Notice that the DMA channel must also be configured, see DMA_CfgChannel().
 *
 * @param[in] descr
 *   Points to the start of a memory area holding the alternate descriptors.
 *
 * @param[in] indx
 *   An alternate descriptor index number to configure (numbered from 0).
 *
 * @param[in] cfg
 *   The configuration to use.
 ******************************************************************************/
void DMA_CfgDescrScatterGather(DMA_DESCRIPTOR_TypeDef *descr,
                               unsigned int indx,
                               DMA_CfgDescrSGAlt_TypeDef *cfg)
{
  uint32_t cycleCtrl;

  EFM_ASSERT(descr);
  EFM_ASSERT(cfg);

  /* Point to a selected entry in the alternate descriptor table. */
  descr += indx;

  if (cfg->srcInc == dmaDataIncNone) {
    descr->SRCEND = cfg->src;
  } else {
    descr->SRCEND = (void *)((uint32_t)(cfg->src)
                             + ((uint32_t)(cfg->nMinus1) << cfg->srcInc));
  }

  if (cfg->dstInc == dmaDataIncNone) {
    descr->DSTEND = cfg->dst;
  } else {
    descr->DSTEND = (void *)((uint32_t)(cfg->dst)
                             + ((uint32_t)(cfg->nMinus1) << cfg->dstInc));
  }

  /* User-definable part not used. */
  descr->USER = 0;

  if (cfg->peripheral) {
    cycleCtrl = (uint32_t)dmaCycleCtrlPerScatterGather + 1;
  } else {
    cycleCtrl = (uint32_t)dmaCycleCtrlMemScatterGather + 1;
  }

  descr->CTRL = (cfg->dstInc << _DMA_CTRL_DST_INC_SHIFT)
                | (cfg->size << _DMA_CTRL_DST_SIZE_SHIFT)
                | (cfg->srcInc << _DMA_CTRL_SRC_INC_SHIFT)
                | (cfg->size << _DMA_CTRL_SRC_SIZE_SHIFT)
                | ((uint32_t)(cfg->hprot) << _DMA_CTRL_SRC_PROT_CTRL_SHIFT)
                | (cfg->arbRate << _DMA_CTRL_R_POWER_SHIFT)
                | ((uint32_t)(cfg->nMinus1) << _DMA_CTRL_N_MINUS_1_SHIFT)
                /* Never set next useburst bit since the descriptor used after the */
                /* alternate descriptor is the primary descriptor which operates on */
                /* memory. If the alternate descriptors need to have useBurst set, this */
                /* is done when setting up the primary descriptor, i.e., when activating. */
                | (0 << _DMA_CTRL_NEXT_USEBURST_SHIFT)
                | (cycleCtrl << _DMA_CTRL_CYCLE_CTRL_SHIFT);
}

/***************************************************************************//**
 * @brief
 *   Enable or disable a DMA channel.
 *
 * @details
 *   Use this function to explicitly enable or disable a DMA channel. A DMA
 *   channel is automatically disabled when the DMA controller has finished a
 *   transaction.
 *
 * @param[in] channel
 *   The DMA channel to enable or disable.
 *
 * @param[in] enable
 *   If 'true', the channel will be enabled. If 'false', the channel will be
 *   disabled.
 ******************************************************************************/
void DMA_ChannelEnable(unsigned int channel, bool enable)
{
  EFM_ASSERT(channel < DMA_CHAN_COUNT);

  if (enable) {
    DMA->CHENS = 1 << channel;
  } else {
    DMA->CHENC = 1 << channel;
  }
}

/***************************************************************************//**
 * @brief
 *   Check if the DMA channel is enabled.
 *
 * @details
 *   The DMA channel is disabled when the DMA controller has finished a DMA
 *   cycle.
 *
 * @param[in] channel
 *   The DMA channel to check.
 *
 * @return
 *   True if the channel is enabled, false if not.
 ******************************************************************************/
bool DMA_ChannelEnabled(unsigned int channel)
{
  EFM_ASSERT(channel < DMA_CHAN_COUNT);

  return (bool)((DMA->CHENS >> channel) & 1);
}

/***************************************************************************//**
 * @brief
 *   Enable or disable a DMA channel request.
 *
 * @details
 *   Use this function to enable or disable a DMA channel request. This will
 *   prevent the DMA from proceeding after its current transaction if disabled.
 *
 * @param[in] channel
 *   The DMA channel to enable or disable the request on.
 *
 * @param[in] enable
 *   If 'true', the request will be enabled. If 'false', the request will be disabled.
 ******************************************************************************/
void DMA_ChannelRequestEnable(unsigned int channel, bool enable)
{
  EFM_ASSERT(channel < DMA_CHAN_COUNT);

  if (enable) {
    BUS_RegBitWrite(&DMA->CHREQMASKC, channel, 1);
  } else {
    BUS_RegBitWrite(&DMA->CHREQMASKS, channel, 1);
  }
}

/***************************************************************************//**
 * @brief
 *   Initialize the DMA controller.
 *
 * @details
 *   This function resets and prepares the DMA controller for use. Although
 *   it may be used several times, it is normally only used during system
 *   initialization. If reused during a normal operation, any ongoing DMA
 *   transfers will be aborted. When complete, the DMA controller is in
 *   an enabled state.
 *
 * @note
 *   Must be invoked before using the DMA controller.
 *
 * @param[in] init
 *   A pointer to a structure containing the DMA initialization information.
 ******************************************************************************/
void DMA_Init(DMA_Init_TypeDef *init)
{
  EFM_ASSERT(init);

  /* Make sure that the control block is properly aligned. */
#if (DMA_CHAN_COUNT <= 4)
  EFM_ASSERT(!((uint32_t)(init->controlBlock) & (128 - 1)));
#elif (DMA_CHAN_COUNT <= 8) || (DMA_CHAN_COUNT <= 12)
  EFM_ASSERT(!((uint32_t)(init->controlBlock) & (256 - 1)));
#else
#error "Unsupported DMA channel count (em_dma.c)."
#endif

  /* Make sure that the DMA clock is enabled prior to accessing the DMA module. */
  CMU_ClockEnable(cmuClock_DMA, true);

  /* Make sure that the DMA controller is set to a known reset state. */
  DMA_Reset();

  /* Clear/enable DMA interrupts. */
  NVIC_ClearPendingIRQ(DMA_IRQn);
  NVIC_EnableIRQ(DMA_IRQn);

  /* Enable the bus error interrupt. */
  DMA->IEN = DMA_IEN_ERR;

  /* Set the pointer to a control block. Notice that the pointer must have been */
  /* properly aligned according to requirements defined in the reference */
  /* manual. */
  DMA->CTRLBASE = (uint32_t)(init->controlBlock);

  /* Configure and enable the DMA controller. */
  DMA->CONFIG = ((uint32_t)(init->hprot) << _DMA_CONFIG_CHPROT_SHIFT)
                | DMA_CONFIG_EN;
}

/***************************************************************************//**
 * @brief
 *   Refresh a descriptor used in a DMA ping-pong cycle.
 *
 * @details
 *   During a ping-pong DMA cycle, the DMA controller automatically alternates
 *   between the primary and alternate descriptors, when completing use of a
 *   descriptor. While the other descriptor is in use by the DMA controller,
 *   the software should refresh the completed descriptor. This is typically done from
 *   the callback defined for the ping-pong cycle.
 *
 * @param[in] channel
 *   The DMA channel to refresh the ping-pong descriptor for.
 *
 * @param[in] primary
 *   @li true - refresh the primary descriptor
 *   @li false - refresh an alternate descriptor
 *
 * @param[in] useBurst
 *   The burst feature is only used on peripherals supporting DMA bursts.
 *   Bursts must not be used if the total length (as given by nMinus1) is
 *   less than the arbitration rate configured for the descriptor.
 *   See the reference manual for more details on burst usage.
 *
 * @param[in] dst
 *   An address to a start location to transfer data to. If NULL, leave setting in
 *   descriptor as is.
 *
 * @param[in] src
 *   An address to a start location to transfer data from. If NULL, leave setting in
 *   descriptor as is.
 *
 * @param[in] nMinus1
 *   A number of DMA transfer elements (minus 1) to transfer (<= 1023). The
 *   size of the DMA transfer element (1, 2 or 4 bytes) is configured with
 *   DMA_CfgDescr().
 *
 * @param[in] stop
 *   Indicate that the DMA ping-pong cycle stops @b when done using
 *   this descriptor.
 ******************************************************************************/
void DMA_RefreshPingPong(unsigned int channel,
                         bool primary,
                         bool useBurst,
                         void *dst,
                         const void *src,
                         unsigned int nMinus1,
                         bool stop)
{
  DMA_CycleCtrl_TypeDef  cycleCtrl;
  DMA_DESCRIPTOR_TypeDef *descr;
  uint32_t               inc;
  uint32_t               chBit;
  uint32_t               tmp;

  EFM_ASSERT(channel < DMA_CHAN_COUNT);
  EFM_ASSERT(nMinus1 <= (_DMA_CTRL_N_MINUS_1_MASK >> _DMA_CTRL_N_MINUS_1_SHIFT));

  /* The ping-pong DMA cycle may be stopped by issuing a basic cycle type. */
  if (stop) {
    cycleCtrl = dmaCycleCtrlBasic;
  } else {
    cycleCtrl = dmaCycleCtrlPingPong;
  }

  /* Find a descriptor to configure. */
  if (primary) {
    descr = ((DMA_DESCRIPTOR_TypeDef *)(DMA->CTRLBASE)) + channel;
  } else {
    descr = ((DMA_DESCRIPTOR_TypeDef *)(DMA->ALTCTRLBASE)) + channel;
  }

  if (src) {
    inc = (descr->CTRL & _DMA_CTRL_SRC_INC_MASK) >> _DMA_CTRL_SRC_INC_SHIFT;
    if (inc == _DMA_CTRL_SRC_INC_NONE) {
      descr->SRCEND = (volatile void*)src;
    } else {
      descr->SRCEND = (void *)((uint32_t)src + (nMinus1 << inc));
    }
  }

  if (dst) {
    inc = (descr->CTRL & _DMA_CTRL_DST_INC_MASK) >> _DMA_CTRL_DST_INC_SHIFT;
    if (inc == _DMA_CTRL_DST_INC_NONE) {
      descr->DSTEND = dst;
    } else {
      descr->DSTEND = (void *)((uint32_t)dst + (nMinus1 << inc));
    }
  }

  chBit = 1 << channel;
  if (useBurst) {
    DMA->CHUSEBURSTS = chBit;
  } else {
    DMA->CHUSEBURSTC = chBit;
  }

  /* Set cycle control. */
  tmp  = descr->CTRL & ~(_DMA_CTRL_CYCLE_CTRL_MASK | _DMA_CTRL_N_MINUS_1_MASK);
  tmp |= nMinus1 << _DMA_CTRL_N_MINUS_1_SHIFT;
  tmp |= cycleCtrl << _DMA_CTRL_CYCLE_CTRL_SHIFT;
  descr->CTRL = tmp;
}

/***************************************************************************//**
 * @brief
 *   Reset the DMA controller.
 *
 * @details
 *   This functions will disable the DMA controller and set it to a reset
 *   state.
 *
 * @note
 *   Note that any ongoing transfers will be aborted.
 ******************************************************************************/
void DMA_Reset(void)
{
  int i;

  /* Disable DMA interrupts */
  NVIC_DisableIRQ(DMA_IRQn);

  /* Put the DMA controller into a known state, first disabling it. */
  DMA->CONFIG      = _DMA_CONFIG_RESETVALUE;
  DMA->CHUSEBURSTC = _DMA_CHUSEBURSTC_MASK;
  DMA->CHREQMASKC  = _DMA_CHREQMASKC_MASK;
  DMA->CHENC       = _DMA_CHENC_MASK;
  DMA->CHALTC      = _DMA_CHALTC_MASK;
  DMA->CHPRIC      = _DMA_CHPRIC_MASK;
  DMA->ERRORC      = DMA_ERRORC_ERRORC;
  DMA->IEN         = _DMA_IEN_RESETVALUE;
  DMA->IFC         = _DMA_IFC_MASK;

  /* Clear channel control flags. */
  for (i = 0; i < DMA_CHAN_COUNT; i++) {
    DMA->CH[i].CTRL = _DMA_CH_CTRL_RESETVALUE;
  }
}

/** @} (end addtogroup dma) */
#endif /* defined( DMA_PRESENT ) */