schedulerbasicp.nc

tinyos-2.x.rar

// $Id: SchedulerBasicP.nc,v 1.1 2008/06/12 14:02:47 klueska Exp $

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/**
 * SchedulerBasicP implements the default TinyOS scheduler sequence, as
 * documented in TEP 106.
 *
 * @author Philip Levis
 * @author Cory Sharp
 * @author Kevin Klues <[e-mail]>
 * @date   January 19 2005
 */

#include "hardware.h"
#include "thread.h"

module SchedulerBasicP {
  provides interface TaskScheduler;
  provides interface TaskBasic[uint8_t id];
  uses interface ThreadScheduler;
  uses interface Leds;
}
implementation {
  enum {
    NUM_TASKS = uniqueCount("TinyTaskSchedulerC.TaskBasic"),
    NO_TASK = 255,
  };

  volatile uint8_t m_head;
  volatile uint8_t m_tail;
  volatile uint8_t m_next[NUM_TASKS];

  // Helper functions (internal functions) intentionally do not have atomic
  // sections.  It is left as the duty of the exported interface functions to
  // manage atomicity to minimize chances for binary code bloat.

  // move the head forward
  // if the head is at the end, mark the tail at the end, too
  // mark the task as not in the queue
  inline uint8_t popTask() {
    if( m_head != NO_TASK ) {
      uint8_t id = m_head;
      m_head = m_next[m_head];
      if( m_head == NO_TASK ) {
	    m_tail = NO_TASK;
      }
      m_next[id] = NO_TASK;
      return id;
    }
    else {
      return NO_TASK;
    }
  }
  
  bool isWaiting( uint8_t id ) {
    return (m_next[id] != NO_TASK) || (m_tail == id);
  }
  
  async command bool TaskScheduler.hasTasks() {
    atomic return (m_head != NO_TASK);
  }

  bool pushTask( uint8_t id ) {
    if( !isWaiting(id) ) {
      if( m_head == NO_TASK ) {
	    m_head = id;
	    m_tail = id;
      }
      else {
	    m_next[m_tail] = id;
	    m_tail = id;
      }
      return TRUE;
    }
    else {
      return FALSE;
    }
  }
  
  command void TaskScheduler.init() {
    atomic {
      memset( (void *)m_next, NO_TASK, sizeof(m_next) );
      m_head = NO_TASK;
      m_tail = NO_TASK;
    }
  }
  
  command bool TaskScheduler.runNextTask() {
    uint8_t nextTask;
    atomic {
      nextTask = popTask();
      if( nextTask == NO_TASK ) {
	    return FALSE;
      }
    }
    signal TaskBasic.runTask[nextTask]();
    return TRUE;
  }

  command void TaskScheduler.taskLoop() {
    for (;;) {
      uint8_t nextTask;

      atomic {
	    while((nextTask = popTask()) == NO_TASK) {
	      call ThreadScheduler.suspendCurrentThread();
	    }
      }
      signal TaskBasic.runTask[nextTask]();
    }
  }

  /**
   * Return SUCCESS if the post succeeded, EBUSY if it was already posted.
   */
  
  async command error_t TaskBasic.postTask[uint8_t id]() {
    atomic { return pushTask(id) ? SUCCESS : EBUSY; }
  }

  default event void TaskBasic.runTask[uint8_t id]() {}
}