/*
    ChibiOS - Copyright (C) 2006..2015 Giovanni Di Sirio.

    This file is part of ChibiOS.

    ChibiOS 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.

    ChibiOS 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/>.
*/

/**
 * @file    chmboxes.c
 * @brief   Mailboxes code.
 *
 * @addtogroup mailboxes
 * @details Asynchronous messages.
 *          <h2>Operation mode</h2>
 *          A mailbox is an asynchronous communication mechanism.<br>
 *          Operations defined for mailboxes:
 *          - <b>Post</b>: Posts a message on the mailbox in FIFO order.
 *          - <b>Post Ahead</b>: Posts a message on the mailbox with urgent
 *            priority.
 *          - <b>Fetch</b>: A message is fetched from the mailbox and removed
 *            from the queue.
 *          - <b>Reset</b>: The mailbox is emptied and all the stored messages
 *            are lost.
 *          .
 *          A message is a variable of type msg_t that is guaranteed to have
 *          the same size of and be compatible with (data) pointers (anyway an
 *          explicit cast is needed).
 *          If larger messages need to be exchanged then a pointer to a
 *          structure can be posted in the mailbox but the posting side has
 *          no predefined way to know when the message has been processed. A
 *          possible approach is to allocate memory (from a memory pool for
 *          example) from the posting side and free it on the fetching side.
 *          Another approach is to set a "done" flag into the structure pointed
 *          by the message.
 * @pre     In order to use the mailboxes APIs the @p CH_CFG_USE_MAILBOXES
 *          option must be enabled in @p chconf.h.
 * @note    Compatible with RT and NIL.
 * @{
 */

#include "ch.h"

#if (CH_CFG_USE_MAILBOXES == TRUE) || defined(__DOXYGEN__)

/*===========================================================================*/
/* Module exported variables.                                                */
/*===========================================================================*/

/*===========================================================================*/
/* Module local types.                                                       */
/*===========================================================================*/

/*===========================================================================*/
/* Module local variables.                                                   */
/*===========================================================================*/

/*===========================================================================*/
/* Module local functions.                                                   */
/*===========================================================================*/

/*===========================================================================*/
/* Module exported functions.                                                */
/*===========================================================================*/

/**
 * @brief   Initializes a @p mailbox_t object.
 *
 * @param[out] mbp      the pointer to the @p mailbox_t structure to be
 *                      initialized
 * @param[in] buf       pointer to the messages buffer as an array of @p msg_t
 * @param[in] n         number of elements in the buffer array
 *
 * @init
 */
void chMBObjectInit(mailbox_t *mbp, msg_t *buf, cnt_t n) {

  chDbgCheck((mbp != NULL) && (buf != NULL) && (n > (cnt_t)0));

  mbp->buffer = buf;
  mbp->rdptr = buf;
  mbp->wrptr = buf;
  mbp->top = &buf[n];
  chSemObjectInit(&mbp->emptysem, n);
  chSemObjectInit(&mbp->fullsem, (cnt_t)0);
}

/**
 * @brief   Resets a @p mailbox_t object.
 * @details All the waiting threads are resumed with status @p MSG_RESET and
 *          the queued messages are lost.
 *
 * @param[in] mbp       the pointer to an initialized @p mailbox_t object
 *
 * @api
 */
void chMBReset(mailbox_t *mbp) {

  chSysLock();
  chMBResetI(mbp);
  chSchRescheduleS();
  chSysUnlock();
}

/**
 * @brief   Resets a @p mailbox_t object.
 * @details All the waiting threads are resumed with status @p MSG_RESET and
 *          the queued messages are lost.
 *
 * @param[in] mbp       the pointer to an initialized @p mailbox_t object
 *
 * @api
 */
void chMBResetI(mailbox_t *mbp) {

  chDbgCheckClassI();
  chDbgCheck(mbp != NULL);

  mbp->wrptr = mbp->buffer;
  mbp->rdptr = mbp->buffer;
  chSemResetI(&mbp->emptysem, (cnt_t)(mbp->top - mbp->buffer));
  chSemResetI(&mbp->fullsem, (cnt_t)0);
}

/**
 * @brief   Posts a message into a mailbox.
 * @details The invoking thread waits until a empty slot in the mailbox becomes
 *          available or the specified time runs out.
 *
 * @param[in] mbp       the pointer to an initialized @p mailbox_t object
 * @param[in] msg       the message to be posted on the mailbox
 * @param[in] timeout   the number of ticks before the operation timeouts,
 *                      the following special values are allowed:
 *                      - @a TIME_IMMEDIATE immediate timeout.
 *                      - @a TIME_INFINITE no timeout.
 *                      .
 * @return              The operation status.
 * @retval MSG_OK       if a message has been correctly posted.
 * @retval MSG_RESET    if the mailbox has been reset while waiting.
 * @retval MSG_TIMEOUT  if the operation has timed out.
 *
 * @api
 */
msg_t chMBPost(mailbox_t *mbp, msg_t msg, systime_t timeout) {
  msg_t rdymsg;

  chSysLock();
  rdymsg = chMBPostS(mbp, msg, timeout);
  chSysUnlock();

  return rdymsg;
}

/**
 * @brief   Posts a message into a mailbox.
 * @details The invoking thread waits until a empty slot in the mailbox becomes
 *          available or the specified time runs out.
 *
 * @param[in] mbp       the pointer to an initialized @p mailbox_t object
 * @param[in] msg       the message to be posted on the mailbox
 * @param[in] timeout   the number of ticks before the operation timeouts,
 *                      the following special values are allowed:
 *                      - @a TIME_IMMEDIATE immediate timeout.
 *                      - @a TIME_INFINITE no timeout.
 *                      .
 * @return              The operation status.
 * @retval MSG_OK       if a message has been correctly posted.
 * @retval MSG_RESET    if the mailbox has been reset while waiting.
 * @retval MSG_TIMEOUT  if the operation has timed out.
 *
 * @sclass
 */
msg_t chMBPostS(mailbox_t *mbp, msg_t msg, systime_t timeout) {
  msg_t rdymsg;

  chDbgCheckClassS();
  chDbgCheck(mbp != NULL);

  rdymsg = chSemWaitTimeoutS(&mbp->emptysem, timeout);
  if (rdymsg == MSG_OK) {
    *mbp->wrptr++ = msg;
    if (mbp->wrptr >= mbp->top) {
      mbp->wrptr = mbp->buffer;
    }
    chSemSignalI(&mbp->fullsem);
    chSchRescheduleS();
  }

  return rdymsg;
}

/**
 * @brief   Posts a message into a mailbox.
 * @details This variant is non-blocking, the function returns a timeout
 *          condition if the queue is full.
 *
 * @param[in] mbp       the pointer to an initialized @p mailbox_t object
 * @param[in] msg       the message to be posted on the mailbox
 * @return              The operation status.
 * @retval MSG_OK       if a message has been correctly posted.
 * @retval MSG_TIMEOUT  if the mailbox is full and the message cannot be
 *                      posted.
 *
 * @iclass
 */
msg_t chMBPostI(mailbox_t *mbp, msg_t msg) {

  chDbgCheckClassI();
  chDbgCheck(mbp != NULL);

  if (chSemGetCounterI(&mbp->emptysem) <= (cnt_t)0) {
    return MSG_TIMEOUT;
  }

  chSemFastWaitI(&mbp->emptysem);
  *mbp->wrptr++ = msg;
  if (mbp->wrptr >= mbp->top) {
     mbp->wrptr = mbp->buffer;
  }
  chSemSignalI(&mbp->fullsem);

  return MSG_OK;
}

/**
 * @brief   Posts an high priority message into a mailbox.
 * @details The invoking thread waits until a empty slot in the mailbox becomes
 *          available or the specified time runs out.
 *
 * @param[in] mbp       the pointer to an initialized @p mailbox_t object
 * @param[in] msg       the message to be posted on the mailbox
 * @param[in] timeout   the number of ticks before the operation timeouts,
 *                      the following special values are allowed:
 *                      - @a TIME_IMMEDIATE immediate timeout.
 *                      - @a TIME_INFINITE no timeout.
 *                      .
 * @return              The operation status.
 * @retval MSG_OK       if a message has been correctly posted.
 * @retval MSG_RESET    if the mailbox has been reset while waiting.
 * @retval MSG_TIMEOUT  if the operation has timed out.
 *
 * @api
 */
msg_t chMBPostAhead(mailbox_t *mbp, msg_t msg, systime_t timeout) {
  msg_t rdymsg;

  chSysLock();
  rdymsg = chMBPostAheadS(mbp, msg, timeout);
  chSysUnlock();

  return rdymsg;
}

/**
 * @brief   Posts an high priority message into a mailbox.
 * @details The invoking thread waits until a empty slot in the mailbox becomes
 *          available or the specified time runs out.
 *
 * @param[in] mbp       the pointer to an initialized @p mailbox_t object
 * @param[in] msg       the message to be posted on the mailbox
 * @param[in] timeout   the number of ticks before the operation timeouts,
 *                      the following special values are allowed:
 *                      - @a TIME_IMMEDIATE immediate timeout.
 *                      - @a TIME_INFINITE no timeout.
 *                      .
 * @return              The operation status.
 * @retval MSG_OK       if a message has been correctly posted.
 * @retval MSG_RESET    if the mailbox has been reset while waiting.
 * @retval MSG_TIMEOUT  if the operation has timed out.
 *
 * @sclass
 */
msg_t chMBPostAheadS(mailbox_t *mbp, msg_t msg, systime_t timeout) {
  msg_t rdymsg;

  chDbgCheckClassS();
  chDbgCheck(mbp != NULL);

  rdymsg = chSemWaitTimeoutS(&mbp->emptysem, timeout);
  if (rdymsg == MSG_OK) {
    if (--mbp->rdptr < mbp->buffer) {
      mbp->rdptr = mbp->top - 1;
    }
    *mbp->rdptr = msg;
    chSemSignalI(&mbp->fullsem);
    chSchRescheduleS();
  }

  return rdymsg;
}

/**
 * @brief   Posts an high priority message into a mailbox.
 * @details This variant is non-blocking, the function returns a timeout
 *          condition if the queue is full.
 *
 * @param[in] mbp       the pointer to an initialized @p mailbox_t object
 * @param[in] msg       the message to be posted on the mailbox
 * @return              The operation status.
 * @retval MSG_OK       if a message has been correctly posted.
 * @retval MSG_TIMEOUT  if the mailbox is full and the message cannot be
 *                      posted.
 *
 * @iclass
 */
msg_t chMBPostAheadI(mailbox_t *mbp, msg_t msg) {

  chDbgCheckClassI();
  chDbgCheck(mbp != NULL);

  if (chSemGetCounterI(&mbp->emptysem) <= (cnt_t)0) {
    return MSG_TIMEOUT;
  }
  chSemFastWaitI(&mbp->emptysem);
  if (--mbp->rdptr < mbp->buffer) {
    mbp->rdptr = mbp->top - 1;
  }
  *mbp->rdptr = msg;
  chSemSignalI(&mbp->fullsem);

  return MSG_OK;
}

/**
 * @brief   Retrieves a message from a mailbox.
 * @details The invoking thread waits until a message is posted in the mailbox
 *          or the specified time runs out.
 *
 * @param[in] mbp       the pointer to an initialized @p mailbox_t object
 * @param[out] msgp     pointer to a message variable for the received message
 * @param[in] timeout   the number of ticks before the operation timeouts,
 *                      the following special values are allowed:
 *                      - @a TIME_IMMEDIATE immediate timeout.
 *                      - @a TIME_INFINITE no timeout.
 *                      .
 * @return              The operation status.
 * @retval MSG_OK       if a message has been correctly fetched.
 * @retval MSG_RESET    if the mailbox has been reset while waiting.
 * @retval MSG_TIMEOUT  if the operation has timed out.
 *
 * @api
 */
msg_t chMBFetch(mailbox_t *mbp, msg_t *msgp, systime_t timeout) {
  msg_t rdymsg;

  chSysLock();
  rdymsg = chMBFetchS(mbp, msgp, timeout);
  chSysUnlock();

  return rdymsg;
}

/**
 * @brief   Retrieves a message from a mailbox.
 * @details The invoking thread waits until a message is posted in the mailbox
 *          or the specified time runs out.
 *
 * @param[in] mbp       the pointer to an initialized @p mailbox_t object
 * @param[out] msgp     pointer to a message variable for the received message
 * @param[in] timeout   the number of ticks before the operation timeouts,
 *                      the following special values are allowed:
 *                      - @a TIME_IMMEDIATE immediate timeout.
 *                      - @a TIME_INFINITE no timeout.
 *                      .
 * @return              The operation status.
 * @retval MSG_OK       if a message has been correctly fetched.
 * @retval MSG_RESET    if the mailbox has been reset while waiting.
 * @retval MSG_TIMEOUT  if the operation has timed out.
 *
 * @sclass
 */
msg_t chMBFetchS(mailbox_t *mbp, msg_t *msgp, systime_t timeout) {
  msg_t rdymsg;

  chDbgCheckClassS();
  chDbgCheck((mbp != NULL) && (msgp != NULL));

  rdymsg = chSemWaitTimeoutS(&mbp->fullsem, timeout);
  if (rdymsg == MSG_OK) {
    *msgp = *mbp->rdptr++;
    if (mbp->rdptr >= mbp->top) {
      mbp->rdptr = mbp->buffer;
    }
    chSemSignalI(&mbp->emptysem);
    chSchRescheduleS();
  }

  return rdymsg;
}

/**
 * @brief   Retrieves a message from a mailbox.
 * @details This variant is non-blocking, the function returns a timeout
 *          condition if the queue is empty.
 *
 * @param[in] mbp       the pointer to an initialized @p mailbox_t object
 * @param[out] msgp     pointer to a message variable for the received message
 * @return              The operation status.
 * @retval MSG_OK       if a message has been correctly fetched.
 * @retval MSG_TIMEOUT  if the mailbox is empty and a message cannot be
 *                      fetched.
 *
 * @iclass
 */
msg_t chMBFetchI(mailbox_t *mbp, msg_t *msgp) {

  chDbgCheckClassI();
  chDbgCheck((mbp != NULL) && (msgp != NULL));

  if (chSemGetCounterI(&mbp->fullsem) <= (cnt_t)0) {
    return MSG_TIMEOUT;
  }
  chSemFastWaitI(&mbp->fullsem);
  *msgp = *mbp->rdptr++;
  if (mbp->rdptr >= mbp->top) {
    mbp->rdptr = mbp->buffer;
  }
  chSemSignalI(&mbp->emptysem);

  return MSG_OK;
}
#endif /* CH_CFG_USE_MAILBOXES == TRUE */

/** @} */