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/*

 *  Thread Handler

 *

 *

 *  COPYRIGHT (c) 1989-1999.

 *  On-Line Applications Research Corporation (OAR).

 *

 *  The license and distribution terms for this file may be

 *  found in found in the file LICENSE in this distribution or at

 *  http://www.OARcorp.com/rtems/license.html.

 *

 *  $Id: threaddispatch.c,v 1.2 2001-09-27 11:59:34 chris Exp $

 */

#include <rtems/system.h>

#include <rtems/score/apiext.h>

#include <rtems/score/context.h>

#include <rtems/score/interr.h>

#include <rtems/score/isr.h>

#include <rtems/score/object.h>

#include <rtems/score/priority.h>

#include <rtems/score/states.h>

#include <rtems/score/sysstate.h>

#include <rtems/score/thread.h>

#include <rtems/score/threadq.h>

#include <rtems/score/userext.h>

#include <rtems/score/wkspace.h>

/*PAGE

 *

 *  _Thread_Dispatch

 *

 *  This kernel routine determines if a dispatch is needed, and if so

 *  dispatches to the heir thread.  Once the heir is running an attempt

 *  is made to dispatch any ASRs.

 *

 *  ALTERNATE ENTRY POINTS:

 *    void _Thread_Enable_dispatch();

 *

 *  Input parameters:  NONE

 *

 *  Output parameters:  NONE

 *

 *  INTERRUPT LATENCY:

 *    dispatch thread

 *    no dispatch thread

 */

#if ( CPU_INLINE_ENABLE_DISPATCH == FALSE )

void _Thread_Enable_dispatch( void )

{

  if ( --_Thread_Dispatch_disable_level )

    return;

  _Thread_Dispatch();

}

#endif

void _Thread_Dispatch( void )

{

  Thread_Control   *executing;

  Thread_Control   *heir;

  ISR_Level         level;

  executing   = _Thread_Executing;

  _ISR_Disable( level );

  while ( _Context_Switch_necessary == TRUE ) {

    heir = _Thread_Heir;

    _Thread_Dispatch_disable_level = 1;

    _Context_Switch_necessary = FALSE;

    _Thread_Executing = heir;

    executing->rtems_ada_self = rtems_ada_self;

    rtems_ada_self = heir->rtems_ada_self;

    _ISR_Enable( level );

    heir->ticks_executed++;

    _User_extensions_Thread_switch( executing, heir );

    if ( heir->budget_algorithm == THREAD_CPU_BUDGET_ALGORITHM_RESET_TIMESLICE )

      heir->cpu_time_budget = _Thread_Ticks_per_timeslice;

    /*

     *  If the CPU has hardware floating point, then we must address saving

     *  and restoring it as part of the context switch.

     *

     *  The second conditional compilation section selects the algorithm used

     *  to context switch between floating point tasks.  The deferred algorithm

     *  can be significantly better in a system with few floating point tasks

     *  because it reduces the total number of save and restore FP context

     *  operations.  However, this algorithm can not be used on all CPUs due

     *  to unpredictable use of FP registers by some compilers for integer

     *  operations.

     */

#if ( CPU_HARDWARE_FP == TRUE )

#if ( CPU_USE_DEFERRED_FP_SWITCH == TRUE )

    if ( (heir->fp_context != NULL) && !_Thread_Is_allocated_fp( heir ) ) {

      if ( _Thread_Allocated_fp != NULL )

        _Context_Save_fp( &_Thread_Allocated_fp->fp_context );

      _Context_Restore_fp( &heir->fp_context );

      _Thread_Allocated_fp = heir;

    }

#else

    if ( executing->fp_context != NULL )

      _Context_Save_fp( &executing->fp_context );

    if ( heir->fp_context != NULL )

      _Context_Restore_fp( &heir->fp_context );

#endif

#endif

    _Context_Switch( &executing->Registers, &heir->Registers );

    executing = _Thread_Executing;

    _ISR_Disable( level );

  }

  _Thread_Dispatch_disable_level = 0;

  _ISR_Enable( level );

  if ( _Thread_Do_post_task_switch_extension ||

       executing->do_post_task_switch_extension ) {

    executing->do_post_task_switch_extension = FALSE;

    _API_extensions_Run_postswitch();

  }

}