/*
    ChibiOS/RT - Copyright (C) 2006,2007,2008,2009,2010 Giovanni Di Sirio.

    This file is part of ChibiOS/RT.

    ChibiOS/RT 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/RT 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 as
 *          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_USE_MAILBOXES option
 *          must be enabled in @p chconf.h.
 * @{
 */

#include "ch.h"

#if CH_USE_MAILBOXES || defined(__DOXYGEN__)
/**
 * @brief   Initializes a Mailbox object.
 *
 * @param[out] mbp      the pointer to the Mailbox structure to be initialized
 * @param[in] buf       the circular messages buffer
 * @param[in] n         the buffer size as number of @p msg_t
 *
 * @init
 */
void chMBInit(Mailbox *mbp, msg_t *buf, cnt_t n) {

  chDbgCheck((mbp != NULL) && (buf != NULL) && (n > 0), "chMBInit");

  mbp->mb_buffer = mbp->mb_wrptr = mbp->mb_rdptr = buf;
  mbp->mb_top = &buf[n];
  chSemInit(&mbp->mb_emptysem, n);
  chSemInit(&mbp->mb_fullsem, 0);
}

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

  chDbgCheck(mbp != NULL, "chMBReset");

  chSysLock();
  mbp->mb_wrptr = mbp->mb_rdptr = mbp->mb_buffer;
  chSemResetI(&mbp->mb_emptysem, mbp->mb_top - mbp->mb_buffer);
  chSemResetI(&mbp->mb_fullsem, 0);
  chSchRescheduleS();
  chSysUnlock();
}

/**
 * @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 Mailbox object
 * @param[in] msg       the message to be posted on the mailbox
 * @param[in] time      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 RDY_OK       if a message has been correctly posted.
 * @retval RDY_RESET    if the mailbox has been reset while waiting.
 * @retval RDY_TIMEOUT  if the operation has timed out.
 *
 * @api
 */
msg_t chMBPost(Mailbox *mbp, msg_t msg, systime_t time) {
  msg_t rdymsg;

  chSysLock();
  rdymsg = chMBPostS(mbp, msg, time);
  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 Mailbox object
 * @param[in] msg       the message to be posted on the mailbox
 * @param[in] time      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 RDY_OK       if a message has been correctly posted.
 * @retval RDY_RESET    if the mailbox has been reset while waiting.
 * @retval RDY_TIMEOUT  if the operation has timed out.
 *
 * @sclass
 */
msg_t chMBPostS(Mailbox *mbp, msg_t msg, systime_t time) {
  msg_t rdymsg;

  chDbgCheck(mbp != NULL, "chMBPostS");

  rdymsg = chSemWaitTimeoutS(&mbp->mb_emptysem, time);
  if (rdymsg == RDY_OK) {
    *mbp->mb_wrptr++ = msg;
    if (mbp->mb_wrptr >= mbp->mb_top)
      mbp->mb_wrptr = mbp->mb_buffer;
    chSemSignalI(&mbp->mb_fullsem);
    chSchRescheduleS();
  }
  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 Mailbox object
 * @param[in] msg       the message to be posted on the mailbox
 * @param[in] time      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 RDY_OK       if a message has been correctly posted.
 * @retval RDY_RESET    if the mailbox has been reset while waiting.
 * @retval RDY_TIMEOUT  if the operation has timed out.
 *
 * @api
 */
msg_t chMBPostAhead(Mailbox *mbp, msg_t msg, systime_t time) {
  msg_t rdymsg;

  chSysLock();
  rdymsg = chMBPostAheadS(mbp, msg, time);
  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 Mailbox object
 * @param[in] msg       the message to be posted on the mailbox
 * @param[in] time      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 RDY_OK       if a message has been correctly posted.
 * @retval RDY_RESET    if the mailbox has been reset while waiting.
 * @retval RDY_TIMEOUT  if the operation has timed out.
 *
 * @sclass
 */
msg_t chMBPostAheadS(Mailbox *mbp, msg_t msg, systime_t time) {
  msg_t rdymsg;

  chDbgCheck(mbp != NULL, "chMBPostAheadS");

  rdymsg = chSemWaitTimeoutS(&mbp->mb_emptysem, time);
  if (rdymsg == RDY_OK) {
    if (--mbp->mb_rdptr < mbp->mb_buffer)
      mbp->mb_rdptr = mbp->mb_top - 1;
    *mbp->mb_rdptr = msg;
    chSemSignalI(&mbp->mb_fullsem);
    chSchRescheduleS();
  }
  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 Mailbox object
 * @param[out] msgp     pointer to a message variable for the received message
 * @param[in] time      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 RDY_OK       if a message has been correctly fetched.
 * @retval RDY_RESET    if the mailbox has been reset while waiting.
 * @retval RDY_TIMEOUT  if the operation has timed out.
 *
 * @api
 */
msg_t chMBFetch(Mailbox *mbp, msg_t *msgp, systime_t time) {
  msg_t rdymsg;

  chSysLock();
  rdymsg = chMBFetchS(mbp, msgp, time);
  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 Mailbox object
 * @param[out] msgp     pointer to a message variable for the received message
 * @param[in] time      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 RDY_OK       if a message has been correctly fetched.
 * @retval RDY_RESET    if the mailbox has been reset while waiting.
 * @retval RDY_TIMEOUT  if the operation has timed out.
 *
 * @sclass
 */
msg_t chMBFetchS(Mailbox *mbp, msg_t *msgp, systime_t time) {
  msg_t rdymsg;

  chDbgCheck((mbp != NULL) && (msgp != NULL), "chMBFetchS");

  rdymsg = chSemWaitTimeoutS(&mbp->mb_fullsem, time);
  if (rdymsg == RDY_OK) {
    *msgp = *mbp->mb_rdptr++;
    if (mbp->mb_rdptr >= mbp->mb_top)
      mbp->mb_rdptr = mbp->mb_buffer;
    chSemSignalI(&mbp->mb_emptysem);
    chSchRescheduleS();
  }
  return rdymsg;
}
#endif /* CH_USE_MAILBOXES */

/** @} */