/* Copyright (C) 2004 David Decotigny
 
    This program 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 2
    of the License, or (at your option) any later version.
    
    This program 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, write to the Free Software
    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
    USA. 
 */
 #ifndef _SOS_SCHED_H_
 #define _SOS_SCHED_H_
 
 
 /**
  * @file sched.h
  *
  * A basic scheduler inspired from the O(1) Linux scheduler. Supports
  * 2 classes of thread priorities:
  *  - so-called 'real-time' threads scheduled according to a simple
  *    traditional static priority real-time scheduler. "Real-time" round
  *    robin scheduling is not supported.
  * - "fair" time-sharing scheduling for non real-time threads. "fair"
  *    because no starvation among the non real-time threads is
  *    possible. Contrary to the original O(1) Linux scheduler, the
  *    on-line adjustment of the scheduling priorities to cope with
  *    interactive/non interactive threads discrimination is not
  *    supported: threads keep having the same priority as long as the
  *    user does not change it.
  *
  * The functions below manage CPU queues, and are NEVER responsible
  * for context switches (see thread.h for that) or synchronizations
  * (see kwaitq.h or the higher levels primitives [mutex, semaphore,
  * ...] for that).
  *
  * @note IMPORTANT: all the functions below are meant to be called
  * ONLY by the thread/timer/kwaitq subsystems. DO NOT use them
  * directly from anywhere else: use ONLY the thread/kwaitq functions!
  * If you still want to call them directly despite this disclaimer,
  * simply disable interrupts before clling them.
  */
 
 #include <sos/errno.h>
 #include <sos/time.h>
 
 
 /**
  * The definition of a priority
  */
 typedef unsigned char sos_sched_priority_t;
 
 
 #include <sos/thread.h>
 
 
 /**
  * Valid priority interval ("real-time" and non real-time threads altogether)
  */
 #define SOS_SCHED_PRIO_HIGHEST 0
 #define SOS_SCHED_PRIO_LOWEST  63
 #define SOS_SCHED_NUM_PRIO     64
 
 
 /**
  * Class-specific priorities
  */
 #define SOS_SCHED_PRIO_RT_HIGHEST 0  /**< Highest 'real-time' static prio. */
 #define SOS_SCHED_PRIO_RT_LOWEST  15 /**< Lowest 'real-time' static priority */
 #define SOS_SCHED_PRIO_TS_HIGHEST 16 /**< Highest time-sharing priority */
 #define SOS_SCHED_PRIO_TS_LOWEST  63 /**< Lowest time-sharing priority */
 
 #define SOS_SCHED_PRIO_DEFAULT 40    /**< Default priority */
 
 
 /**
  * Helper macros (Yes, priorities ordered in decreasing numerical value)
  *
  * @note: The use of this function is RESERVED
  */
 #define SOS_SCHED_PRIO_CMP(prio1,prio2)  ((prio1) - (prio2))
 
 #define SOS_SCHED_PRIO_IS_VALID(prio) \
   ({ int __prio = (int)(prio); \
      ((__prio) <= SOS_SCHED_PRIO_LOWEST) \
       && \
      ((__prio) >= SOS_SCHED_PRIO_HIGHEST); })
 
 #define SOS_SCHED_PRIO_IS_RT(prio)    \
   ({ int __prio = (int)(prio); \
      ((__prio) <= SOS_SCHED_PRIO_RT_LOWEST) \
       && \
      ((__prio) >= SOS_SCHED_PRIO_RT_HIGHEST); })
 
 
 /**
  * The time slices for 'time-sharing' user threads, in ms
  */
 #define SOS_TIME_SLICE_MIN  10 /* for SOS_SCHED_PRIO_TS_HIGHEST */
 #define SOS_TIME_SLICE_MAX 200 /* for SOS_SCHED_PRIO_TS_LOWEST */
 
 
 /**
  * Initialize the scheduler
  *
  * @note: The use of this function is RESERVED
  */
 sos_ret_t sos_sched_subsystem_setup(void);
 
 
 /**
  * Mark the given thread as ready
  *
  * @note: The use of this function is RESERVED
  */
 sos_ret_t sos_sched_set_ready(struct sos_thread * thr);
 
 
 /**
  * Return the identifier of the next thread to run. Also removes it
  * from the ready list, but does NOT set is as current_thread !
  *
  * @param current_thread TCB of the thread calling the function
  *
  * @param do_yield When TRUE, put the current executing thread at the
  * end of the ready list. Otherwise it is kept at the head of it.
  *
  * @note: The use of this function is RESERVED
  */
 struct sos_thread * sos_reschedule(struct sos_thread * current_thread,
                                     sos_bool_t do_yield);
 
 /**
  * Called by thread subsystem each time a READY thread's priority is
  * changed
  *
  * @note: The use of this function is RESERVED (to thread.c)
  */
 sos_ret_t sos_sched_change_priority(struct sos_thread * thr,
                                     sos_sched_priority_t priority);
 
 
 /**
  * Account for the execution of a time tick. Should be called
  * immediately before the timer ISR calls sos_reschedule() before
  * returning to thread context.
  *
  * @note The use of this function is RESERVED (to timer IRQ)
  */
 sos_ret_t sos_sched_do_timer_tick(void);
 
 #endif /* _SOS_WAITQUEUE_H_ */