/************************************************************************
*
*  Module name         : MESSAGE.C
*
*  Module description  :
*     This module manages inter-task message communication.
*
*  Project             : RTMK
*
*  Target platform     : DOS
*
*  Compiler & Library  : BC++ 3.1
*
*  Author              : Richard Shen
*
*  Creation date       : 17 August, 1995
*
************************************************************************/
#include <memory.h>
#include <rtmk.h>
#include "rtmkloc.h"

/************************************************************************
*  Function name   : RtmkPut
*  Description     : Send a message to the destination task
*                  :
*  Parameters      : process  - Destination task control block
*                  : message  - Message buffer
*  Returns         : -
*  Author          : Richard Shen
* -----------------------------------------------------------------------
*  Date     By      Description
* -----------------------------------------------------------------------
*  17Aug95  RCS     Created.
*  06Sep95  RCS     Provide multi-process waiting on sending message
************************************************************************/
void RtmkPut(PROCESS process, void *message)
{
   if (process->msgPending)
   {
      PROCESS p = process;
      /*
         If the destination task has a unread pending message, the message
         originating task will preempted
      */
      while (p->msgSender)
         p = p->msgSender;
      p->msgSender  = curProcess;            /* Save message sender    */
      while (process->msgPending)
      {
         DisableInterrupt();
         readyProcess &= ~curProcess->procMask; /* Say process not ready  */
         EnableInterrupt();
         Scheduler(NULL, FALSE);                /* Switch to other task   */
      } /* end-of-while */
   } /* end of if */

   process->msgPending = TRUE;               /* Message arrived         */
   DisableInterrupt();
   readyProcess       |= process->procMask;  /* Process is ready to run */
   EnableInterrupt();

   /* Copy message to message buffer of destination tasks */
   memcpy(process->msgBuf, (char *)message, MSG_BUF_SZ);

   if (curProcess->priority < process->priority)
   {
      /* Priority is higher than the current process, switch to it */
      Scheduler(process, FALSE);
   } /* end of if */
} /* RtmkPut() */

/************************************************************************
*  Function name   : RtmkGet
*  Description     : Wait for a message and read message when arrived
*                  :
*  Parameters      : message  - Message buffer to read from
*  Returns         : -
*  Author          : Richard Shen
* -----------------------------------------------------------------------
*  Date     By      Description
* -----------------------------------------------------------------------
*  17Aug95  RCS     Created.
*  06Sep95  RCS     Provide multi-process waiting on sending message
************************************************************************/
void *RtmkGet(void *message)
{
   while (curProcess->msgPending == FALSE)
   {
      /* Message not arrived */
      DisableInterrupt();
      readyProcess &= ~curProcess->procMask; /* Say process not ready  */
      EnableInterrupt();
      if (curProcess->evWait && curProcess->evReceived)
      {
         /* Process ready flag is set by the arrival of an event */
         return(NULL);
      } /* end of if */

      Scheduler(NULL, FALSE);                /* Switch to next process */
   } /* end of while */

   /* Message arrived, copy message to data buffer */
   memcpy((char *)message, curProcess->msgBuf, MSG_BUF_SZ);
   curProcess->msgPending = FALSE;

   /* Resume ready state of messsage sender */
   if (curProcess->msgSender)
   {
      DisableInterrupt();
      readyProcess         |= curProcess->msgSender->procMask;
      curProcess->msgSender = curProcess->msgSender->msgSender;
      EnableInterrupt();
   } /* end of if */

   return(message);
} /* RtmkGet() */

/************************************************************************
*  Function name   : RtmkEmpty
*  Description     : Premitive returns the status of task's pending
*                  : message buffer
*  Parameters      : -
*  Returns         : FALSE, if there is a pending unread inter-task
*                  : message.  Otherwise TRUE.
*  Author          : Richard Shen
* -----------------------------------------------------------------------
*  Date     By      Description
* -----------------------------------------------------------------------
*  17Aug95  RCS     Created.
************************************************************************/
bool RtmkEmpty(void)
{
   if (curProcess->msgPending)
      return(FALSE);

   return(TRUE);
} /* RtmkEmpty() */