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/*
 * Project: S.Ha.R.K.
 *
 * Coordinators:
 *   Giorgio Buttazzo    <giorgio@sssup.it>
 *   Paolo Gai           <pj@gandalf.sssup.it>
 *
 * Authors     :
 *   Paolo Gai           <pj@gandalf.sssup.it>
 *   Massimiliano Giorgi <massy@gandalf.sssup.it>
 *   Luca Abeni          <luca@gandalf.sssup.it>
 *   (see the web pages for full authors list)
 *
 * ReTiS Lab (Scuola Superiore S.Anna - Pisa - Italy)
 *
 * http://www.sssup.it
 * http://retis.sssup.it
 * http://shark.sssup.it
 */

/**
 ------------
 CVS :        $Id: slsh.c,v 1.3 2002-11-11 07:54:33 pj Exp $

 File:        $File$
 Revision:    $Revision: 1.3 $
 Last update: $Date: 2002-11-11 07:54:33 $
 ------------

 This file contains the scheduling module for Slot-Shifting.

 Read slsh.h for further details.

**/

/*
 * Copyright (C) 2000 Paolo Gai
 *
 * 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
 *
 */


#include "slsh.h"
#include <ll/stdio.h>
#include <ll/stdlib.h>
#include <ll/string.h>
#include <ll/math.h>    /* for ceil(...) */
#include <ll/ll.h>      /* for memcpy(...) */
#include <kernel/model.h>
#include <kernel/descr.h>
#include <kernel/var.h>
#include <kernel/func.h>

//#define eslsh_printf kern_printf
#define slsh_printf printk

/* Keeps information about static and guaranteed tasks */
typedef struct {
        int est;
        int dabs;
        int interval;
} SLSH_task;

/*+ Status used in the level +*/
#define SLSH_READY                      MODULE_STATUS_BASE
#define SLSH_WAIT                       MODULE_STATUS_BASE + 1
#define SLSH_IDLE                       MODULE_STATUS_BASE + 2
#define SLSH_WCET_VIOLATED      MODULE_STATUS_BASE + 3

/*+ defines +*/
#define MAX_INTERVALS 1000              /* 1000 intervals is max, for now */

/******+ the level redefinition for the SLOT SHIFT level +*******/
typedef struct {
        level_des l;                    /*+ the standard level descriptor+*/

        /* task lists */
        SLSH_task tasks[MAX_PROC];  /* est and dl's for static and guaranteed task */
       
        IQUEUE idle_statics; /* finished static tasks */
       
        IQUEUE unspecified;     /* tasks with only a wcet */
       
        /* the Intervals list */
        SLSH_interval intervals[MAX_INTERVALS];
        int current;                    /* current interval */
        int last;                       /* last interval */
       
        int slot;                       /* slot shifting time */
        TIME slot_length;       /* slothlength in real system time*/
        int LCM;                        /* length (in slots) of ofline schedule */
       
        int slot_event;         /* save the event */
} SLSH_level_des;


/* Which task models the Slot-Shifting module accepts */
static int SLSH_level_accept_task_model(LEVEL l, TASK_MODEL* m)
{
        HARD_TASK_MODEL* h;
        SOFT_TASK_MODEL* s;

        /* Check the models */
        switch(m->pclass)
        {
                case STATIC_PCLASS:             /* offline scheduled tasks */
                        return 0;
                case HARD_PCLASS:               /* hard aperiodic tasks */
                        h = (HARD_TASK_MODEL *) m;
                        if(h->drel != 0 && h->wcet != 0)        /* must be set */
                                return 0;
                        break;
                case SOFT_PCLASS:               /* soft aperiodic tasks */
                        s = (SOFT_TASK_MODEL *) m;
                        if(s->wcet != 0)                /* must be set */
                                return 0;
                        break;
                default:
        }

        return -1;      /* Not accepted model */
}


static void SLSH_level_status(LEVEL l)
{
        kern_printf("Level status not implemented\n");
}

/* check if some tasks are ready, return 0 if ready, -1 otherwise */
static int SLSH_R(SLSH_task* tasks)
{
        int s;

        /* for all static tasks */
        for(s = 0; tasks[s].est != -1; ++s)
        {
           if(proc_table[s].status == SLSH_READY)
               return 0;
        }
        return -1;
}

/* check if unspecified exists, return 0 if it exists, -1 otherwise */
static int SLSH_T(IQUEUE *unspecified)
{
        if(!iq_isempty(unspecified))
                return 0;
        else
                return -1;
}

/* return the sc in an interval */
static int SLSH_sc(SLSH_interval* intervals, int i)
{
        return intervals[i].sc;
}
/* return a static task from current interval or a guaranted task */
static PID SLSH_staticOrGuaranteed(SLSH_level_des* lev)
{
        int lowest_dl = 0;      /* lowest dl found */
        PID pid = 0;            /* static or guaranteed task */
        int t;

        /* Decide according to EDF, go through all static & guaranteed tasks */
        for(t = 0; t < MAX_PROC; ++t)
        {
                /* static tasks */
                if(proc_table[t].pclass == STATIC_PCLASS)
                {
                        /* static task must belong to current interval */
                        if(lev->tasks[t].interval == lev->current)
                        {
                                /* only ready tasks */
                                if(proc_table[t].status == SLSH_READY)
                                {
                                        /* a new lower dl was found */
                                        if(lev->tasks[t].dabs < lowest_dl)
                                        {
                                                lowest_dl = lev->tasks[t].dabs;
                                                pid = t;
                                        }
                                }
                        }
                } /* guaranteed tasks */
                else if(proc_table[t].pclass == HARD_PCLASS)
                {
                        /* only ready tasks */
                        if(proc_table[t].status == SLSH_READY)
                        {
                                /* a new lower dl was found */
                                if(lev->tasks[t].dabs < lowest_dl)
                                {
                                        lowest_dl = lev->tasks[t].dabs;
                                        pid = t;
                                }
                        }
                }
        }/* for all tasks */
       
        return pid;    
}

/* return a static task among the candidates, all ready statics */
static PID SLSH_candidates(SLSH_task* tasks)
{
        int lowest_dl = 0;
        PID pid;
        int t;

        /* Use the EDL algorithm again to decide which task to run */
        for(t = 0; t < MAX_PROC; ++t)
        {
                /* only static tasks */
                if(proc_table[t].pclass == STATIC_PCLASS)
                {
                        /* only ready tasks */
                        if(proc_table[t].status == SLSH_READY)
                        {      
                                /* a new lower dl was found */
                                if(tasks[t].dabs < lowest_dl)
                                {
                                        lowest_dl = tasks[t].dabs;
                                        pid = t;
                                }
                        }/* all ready tasks */
                }/* all static tasks */
        }/* for all tasks */
       
        return pid;
}

/* decrease the sc in a interval by amount */
void SLSH_decSc(SLSH_interval* intervals, int i, int amount)
{
        intervals[i].sc -= amount;
}

void SLSH_incSc(SLSH_interval* intervals, int i, int amount)
{
        intervals[i].sc += amount;
}

/* swap the sc between intervals, also consider intervals with negative sc */
void SLSH_swapSc(SLSH_interval* intervals, int current, int task_interval)
{
        /* decrease the sc in the current interval */
        SLSH_decSc(intervals, current, 1);
       
        /* update the other interval(s) */
        if(intervals[task_interval].sc < 0)     /* negative sc */
        {
                /* special case, increase next interval sc by 1 and also current interval (borrowing) */
                if(task_interval == current + 1)
                {
                        SLSH_incSc(intervals, task_interval, 1);
                        SLSH_incSc(intervals, current, 1);
                }
                else /* increase every interval sc that is negative between current and task_interval */
                {
                        while(task_interval > current && intervals[task_interval].sc < 0)
                        {
                                SLSH_incSc(intervals, task_interval, 1);
                                task_interval--;
                        }
                }
        }
        else /* ordinary swapping */
                SLSH_incSc(intervals, task_interval, 1);
}

/* The scheduler, decides which task to run. */
static PID SLSH_level_scheduler(LEVEL l)
{
        SLSH_level_des* lev = (SLSH_level_des *)(level_table[l]);
        PID pid;
       
        /* The scheduler choses among static, guaranteed (hard aperiodic) and
             unspecified (soft aperiodic) tasks */
        /* no ready tasks and no sc, execute idle task */
        if(SLSH_R(lev->tasks) == 0 && SLSH_sc(lev->intervals, lev->current) == 0)
                return NIL;
        /* must execute a static from current intervall or a guaranteed task */
        else if(SLSH_R(lev->tasks) > 0 && SLSH_sc(lev->intervals, lev->current) == 0)
                return SLSH_staticOrGuaranteed(lev);
        /* sc available... */
        else if(SLSH_R(lev->tasks) > 0 && SLSH_sc(lev->intervals, lev->current) > 0)
        {
                /* If unspecified exist, execute it according to FIFO order */
                if(SLSH_T(&lev->unspecified) == 0)
                {
                        SLSH_decSc(lev->intervals, lev->current, 1);    /* decrease sc by 1 */
                        return iq_getfirst(&lev->unspecified);
                }
                else /* No unspecified, execute task from candidates (statics) */
                {              
                        pid = SLSH_candidates(lev->tasks);

                        /* sc needs to be swapped */
                        if(lev->tasks[pid].interval != lev->current)
                                SLSH_swapSc(lev->intervals, lev->tasks[pid].interval, lev->current);
                       
                        return pid;            
                }              
        }

        kern_printf("(SLSH s)");
        return NIL;
}

/* not used, slot-shifting handles all guarantees itself, it handles all bandwidth */
static int SLSH_level_guarantee(LEVEL l, bandwidth_t *freebandwidth)
{
        *freebandwidth = 0;
        return 1;
}

/* get the interval that x is in */
static int SLSH_getInterval(SLSH_interval* intervals, int x, int last)
{
        int i;

        /* search through the intervals  */
        for(i = 0; i <= last; ++i)
        {
                /* I is in the interval where start is smaller or equal and end is bigger */           
                if(intervals[i].start <= x && x < intervals[i].end)
                        return i;
        }
        return -1;
}

/* get the start of the interval I */
static int SLSH_intervalStart(SLSH_interval* intervals, int I)
{
        return intervals[I].start;
}

/* split interval I into two parts, slow because of copying. OBS!!! no check if there is
    enough space in the intervals array */
static void SLSH_splitInterval(SLSH_level_des* lev, int I, int dabs)
{
        SLSH_interval left_interval;
        int i;


        lev->last++;
       
        /* move every interval above and including I */
        for(i = lev->last; i > I; --i)
                memcpy(&lev->intervals[i], &lev->intervals[i - 1], sizeof(SLSH_interval));
       
        /* Left interval start, end and length */
        left_interval.start = lev->intervals[I].start;
        left_interval.end = dabs;
        left_interval.length = left_interval.end - left_interval.start;
       
        /* Right interval (uses old interval struct) start and length end remains as the old value */
        lev->intervals[I + 1].start = dabs;
        lev->intervals[I + 1].length = lev->intervals[I + 1].end - lev->intervals[I + 1].start;
       
        /* check if sc still exists in the right interval */
        if(lev->intervals[I + 1].length - lev->intervals[I + 1].maxt > 0)
        {
                lev->intervals[I + 1].sc = lev->intervals[I + 1].length - lev->intervals[I + 1].maxt;
                left_interval.sc = left_interval.length; /* the whole interval is free, for now... */
        }
        else /* no sc in the right interval */
        {
                lev->intervals[I + 1].maxt = lev->intervals[I + 1].length;
                left_interval.sc = lev->intervals[I + 1].sc; /* all sc in left interval */
                lev->intervals[I + 1].sc = 0;
        }        
       
        /* insert the new interval */
        memcpy(&lev->intervals[I], &left_interval, sizeof(SLSH_interval));
}

/* Reduce the sc from back to front by the wcet amount, interval splitting may be neccesary */
static void SLSH_updateSc(SLSH_level_des* lev, HARD_TASK_MODEL* h)
{
        int dabs = ceil((lev->slot + h->drel)/lev->slot_length); /* absolute deadline of request */
        int dabs_interval = SLSH_getInterval(lev->intervals, dabs, lev->last); /* interval where dabs is */
        int C = ceil(h->wcet/lev->slot_length); /* amount of sc to reduce */   
        int sc = 0;
        int i;

        /* check if interval splitting is neccesary */
        if(lev->intervals[dabs_interval].end != dabs)
                SLSH_splitInterval(lev, dabs_interval, dabs);
       
        /* decrease sc in all intervals that are neccesary from dabs_interval o current */
        for(i = dabs_interval; i >= lev->current && C > 0; --i)
        {
                if((sc = SLSH_sc(lev->intervals, i)) >= 0) /* only decrease where sc exists */
                {
                        if(sc > C) /* the last sc dec */
                        {
                                SLSH_decSc(lev->intervals, i, C);
                                C = 0;
                        }
                        else    /* to little sc in this interval, decrease it to 0 */
                        {
                                C -= SLSH_sc(lev->intervals, i);
                                SLSH_decSc(lev->intervals, i, SLSH_sc(lev->intervals, i));
                        }              
                }
        }/* for all intervals */
}

/* the guarantee algorithm for hard aperiodic requests */
static int SLSH_guarantee(SLSH_level_des* lev, HARD_TASK_MODEL* h)
{
        int total_sc = 0;
        int temp, i;
        int dabs = ceil((lev->slot + h->drel)/lev->slot_length); /* absolute deadline of request */
        int dabs_interval = SLSH_getInterval(lev->intervals, dabs, lev->last); /* interval where dabs is */
       
        /* check if the sc up until request deadline is >= request wcet */
        /* 1. the sc of the current interal */
        total_sc = SLSH_sc(lev->intervals, lev->current);

        /* 2. the sc for all whole intervals between current and the interval
            with the request deadline */
        for(i = (lev->current) + 1; i < dabs_interval; ++i)
        {
                if((temp = SLSH_sc(lev->intervals, i)) > 0)
                        total_sc += temp;
        }
       
        /* 3. the min of sc or the execution need in the last interval */
        total_sc += min(SLSH_sc(lev->intervals, dabs_interval),
                                dabs - SLSH_intervalStart(lev->intervals,
                                dabs_interval));

        if(total_sc >= h->wcet)
        {       /* update the sc in the intervals from back to front */
                SLSH_updateSc(lev, h);
                return 0;
        }
        else
                return -1;
}

/* check if task model is accepted and store nessecary parameters */
static int SLSH_task_create(LEVEL l, PID p, TASK_MODEL *m)
{
        SLSH_level_des *lev = (SLSH_level_des *)(level_table[l]);
        STATIC_TASK_MODEL* s;
        HARD_TASK_MODEL* h;
        SOFT_TASK_MODEL* u;

        /* if the SLSH_task_create is called, then the pclass must be a
        valid pclass. Slot-shifting accepts STATIC_TASK, HARD_TASK
        and SOFT_TASK models with some restrictions */

        /* est, dl and wcet is saved in slotlengths */
        switch(m->pclass)
        {      
                case STATIC_PCLASS:     /* offline scheduled tasks */
                        s = (STATIC_TASK_MODEL *) m;
                        lev->tasks[p].est = ceil(s->est/lev->slot_length);             
                        lev->tasks[p].dabs = ceil(s->dabs/lev->slot_length);
                        lev->tasks[p].interval = s->interval;
                        proc_table[p].avail_time = s->wcet;                    
                        proc_table[p].wcet = s->wcet;
                        break;
                case HARD_PCLASS:       /* hard aperiodic tasks */
                        h = (HARD_TASK_MODEL *) m;
                        if(SLSH_guarantee(lev, h) == 0)
                        {
                                /* convert drel to dabs */                     
                                lev->tasks[p].dabs = ceil((lev->slot + h->drel)/lev->slot_length);
                                proc_table[p].avail_time = h->wcet;
                                proc_table[p].wcet = h->wcet;
                        }
                        else /* task not guaranteed */
                                return -1;                     
                        break;
                case SOFT_PCLASS:
                        u = (SOFT_TASK_MODEL *) m;
                        proc_table[p].avail_time = u->wcet;
                        proc_table[p].wcet = u->wcet;
                        iq_insertlast(p, &lev->unspecified);    /* respect FIFO order */
                        break;
                default:        /* a task model not supported */
                        return -1;
        }
        /* enable wcet check in the kernel */
        proc_table[p].control |= CONTROL_CAP;
 
        return 0;
}

static void SLSH_task_detach(LEVEL l, PID p)
{
        /* do nothing */       
}

/* check if a task chosen by scheduler is correct */
static int SLSH_task_eligible(LEVEL l, PID p)
{
        return 0; /* if the task p is chosen, it is always eligible */
}

/************* The slot end event handler *************/
static void SLSH_slot_end(void* p)
{
        SLSH_level_des* lev = (SLSH_level_des *) p;
        PID pid;
        int i;
       
        /* increase slot "time" by 1 */
        if(lev->slot < lev->LCM)
        {
                lev->slot++;
                /* check if new statics are ready */
                for(i = 0; lev->tasks[i].interval != -1; ++i)
                {
                        if(lev->tasks[i].est <= lev->slot && proc_table[i].status == SLSH_WAIT)
                                proc_table[i].status = SLSH_READY;
                }
               
                /* check if current (interval) needs updating */
                if(lev->current < SLSH_getInterval(lev->intervals, lev->slot, lev->last))
                        lev->current++;
               
        }
        else /* restart from the beginning of the offline schedule */
        {
                lev->slot = 0;
               
                while((pid = iq_getfirst(&lev->idle_statics)) != NIL)
                {
                        if(lev->tasks[pid].est <= lev->slot)
                                proc_table[pid].status = SLSH_READY;
                        else
                                proc_table[pid].status = SLSH_WAIT;
                }
        }

        /* call for a rescheduling, reset event flag and increase slot by 1  */
        lev->slot_event = -1;
        kern_printf("*");
        event_need_reschedule();
}

/* when a task becomes executing (EXE status) */
static void SLSH_task_dispatch(LEVEL l, PID pid, int nostop)
{
        SLSH_level_des *lev = (SLSH_level_des *)(level_table[l]);
        struct timespec t;

        /* the task state is set EXE by the scheduler()
        we extract the task from the unspecified queue.
        NB: we can't assume that p is the first task in the queue!!! */
               
        if(proc_table[pid].pclass == SOFT_PCLASS)
                iq_extract(pid, &lev->unspecified);

        /* also start the timer for one slot length */
        lev->slot_event = kern_event_post(&TIME2TIMESPEC(lev->slot_length, t),
                                          SLSH_slot_end, (void*) lev);
}

/* called when task is moved from EXE status */
static void SLSH_task_epilogue(LEVEL l, PID pid)
{
        SLSH_level_des *lev = (SLSH_level_des *)(level_table[l]);

        /* check if the wcet is finished... */
        if (proc_table[pid].avail_time <= 0)
        {
                /* if it is, raise a XWCET_VIOLATION exception */
                kern_raise(XWCET_VIOLATION, pid);
                proc_table[pid].status = SLSH_WCET_VIOLATED;
        }
        else /* the end of a slot. the task returns into the ready queue... */
        {
                if(proc_table[pid].pclass == SOFT_PCLASS)
                        iq_insertfirst(pid,&lev->unspecified);
                       
                proc_table[pid].status = SLSH_READY;
        }
}

/* when task go from SLEEP to SLSH_READY or SLSH_WAIT */
static void SLSH_task_activate(LEVEL l, PID pid)
{
        SLSH_level_des *lev = (SLSH_level_des *)(level_table[l]);
        WORD type = proc_table[pid].pclass;

        /* Test if we are trying to activate a non sleeping task    */
        /* Ignore this; the task is already active                  */
        if (proc_table[pid].status != SLEEP && proc_table[pid].status != SLSH_WCET_VIOLATED)
                return;

        /* make task ready or waiting, dependong on slot (the time) for static tasks only*/
        if(type == STATIC_PCLASS && lev->tasks[pid].est <= lev->slot)
                proc_table[pid].status = SLSH_READY;
        else
                proc_table[pid].status = SLSH_WAIT;
       
        if(type == HARD_PCLASS)
                proc_table[pid].status = SLSH_READY;
       
        /* insert unspecified tasks in QQUEUE and make it ready */
        if(type == SOFT_PCLASS)
        {              
                iq_insertlast(pid ,&lev->unspecified);
                proc_table[pid].status = SLSH_READY;
        }
}

/* when a task i returned to module from a semaphore, mutex ... */
static void SLSH_task_insert(LEVEL l, PID pid)
{
        SLSH_level_des *lev = (SLSH_level_des *)(level_table[l]);

        /* change staus of task */
        proc_table[pid].status = SLSH_READY;
       
        if(proc_table[pid].pclass == SOFT_PCLASS)
                iq_insertfirst(pid ,&lev->unspecified);
}

/* when a semaphore, mutex ... taskes a task from module */
static void SLSH_task_extract(LEVEL l, PID pid)
{
        /* Extract the running task from the level
        . we have already extract it from the ready queue at the dispatch time.
        . the capacity event have to be removed by the generic kernel
        . the wcet don't need modification...
        . the state of the task is set by the calling function
        . the deadline must remain...

        So, we do nothing!!!
        */
}

/* task has finished execution for this period */
static void SLSH_task_endcycle(LEVEL l, PID pid)
{
        /* do nothing */
}

/* the task has finihed its wcet, kill task (dont kill static tasks)  */
static void SLSH_task_end(LEVEL l, PID pid)
{
        SLSH_level_des *lev = (SLSH_level_des *)(level_table[l]);

        if(proc_table[pid].pclass == SOFT_PCLASS)
        {      
                if (proc_table[pid].status == SLSH_READY)
                        iq_extract(pid, &lev->unspecified);
        }
        else if(proc_table[pid].pclass == HARD_PCLASS)
        {
                if (proc_table[pid].status == SLSH_READY)
                        lev->tasks[pid].dabs = 0;
                       
        }
        /* static tasks: put them in idle QUEUE, reset status and avail_time */
        else if(proc_table[pid].pclass == STATIC_PCLASS)
        {
                proc_table[pid].avail_time = proc_table[pid].wcet;
                proc_table[pid].status = SLSH_IDLE;
                iq_priority_insert(pid, &lev->idle_statics);
        }
       
        proc_table[pid].status = FREE;
}

/* called when a task should sleep but not execute for awhile, mabe a mode change */
static void SLSH_task_sleep(LEVEL l, PID pid)
{

        /* the task has terminated his job before it consume the wcet. All OK! */
        proc_table[pid].status = SLEEP;
       
        /* we reset the capacity counters... only for static tasks */
        if (proc_table[pid].pclass == STATIC_PCLASS)
                proc_table[pid].avail_time = proc_table[pid].wcet;
               
}


/** Guest Functions, slot shifing accepts no guests, so all generates exceptions **/

static int SLSH_level_accept_guest_model(LEVEL l, TASK_MODEL* m) { return -1; }

static int SLSH_guest_create(LEVEL l, PID p, TASK_MODEL *m)
{ kern_raise(XINVALID_GUEST,exec_shadow); return 0;     }

static void SLSH_guest_detach(LEVEL l, PID p)
{ kern_raise(XINVALID_GUEST,exec_shadow); }

static void SLSH_guest_dispatch(LEVEL l, PID p, int nostop)
{ kern_raise(XINVALID_GUEST,exec_shadow); }

static void SLSH_guest_epilogue(LEVEL l, PID p)
{ kern_raise(XINVALID_GUEST,exec_shadow); }

static void SLSH_guest_activate(LEVEL l, PID p)
{ kern_raise(XINVALID_GUEST,exec_shadow); }

static void SLSH_guest_insert(LEVEL l, PID p)
{ kern_raise(XINVALID_GUEST,exec_shadow); }

static void SLSH_guest_extract(LEVEL l, PID p)
{ kern_raise(XINVALID_GUEST,exec_shadow); }

static void SLSH_guest_endcycle(LEVEL l, PID p)
{ kern_raise(XINVALID_GUEST,exec_shadow); }

static void SLSH_guest_end(LEVEL l, PID p)
{ kern_raise(XINVALID_GUEST,exec_shadow); }

static void SLSH_guest_sleep(LEVEL l, PID p)
{ kern_raise(XINVALID_GUEST,exec_shadow); }

/******* Registration functions *******/

/*+ Registration function: */
void SLSH_register_level()
{
        LEVEL l;            /* the level that we register */
        SLSH_level_des *lev;  /* for readableness only */
        PID i;              /* a counter */
       
        kern_printf("SLSH_register_level\n");
       
        /* request an entry in the level_table */
        l = level_alloc_descriptor();
       
        /* alloc the space needed for the EDF_level_des */
        lev = (SLSH_level_des *)kern_alloc(sizeof(SLSH_level_des));
       
        /* update the level_table with the new entry */
        level_table[l] = (level_des *)lev;
       
        /* fill the standard descriptor */
        strncpy(lev->l.level_name, SLSH_LEVELNAME, MAX_LEVELNAME);

        lev->l.level_code                       = SLSH_LEVEL_CODE;
        lev->l.level_version                    = SLSH_LEVEL_VERSION;

        lev->l.level_accept_task_model          = SLSH_level_accept_task_model;
        lev->l.level_accept_guest_model         = SLSH_level_accept_guest_model;
        lev->l.level_status                     = SLSH_level_status;
        lev->l.level_scheduler                  = SLSH_level_scheduler;

        lev->l.level_guarantee                  = SLSH_level_guarantee;
       
        lev->l.task_create                      = SLSH_task_create;
        lev->l.task_detach                      = SLSH_task_detach;
        lev->l.task_eligible                    = SLSH_task_eligible;
        lev->l.task_dispatch                    = SLSH_task_dispatch;
        lev->l.task_epilogue                    = SLSH_task_epilogue;
        lev->l.task_activate                    = SLSH_task_activate;
        lev->l.task_insert                      = SLSH_task_insert;
        lev->l.task_extract                     = SLSH_task_extract;
        lev->l.task_endcycle                    = SLSH_task_endcycle;
        lev->l.task_end                         = SLSH_task_end;
        lev->l.task_sleep                       = SLSH_task_sleep;
       
        lev->l.guest_create                     = SLSH_guest_create;
        lev->l.guest_detach                     = SLSH_guest_detach;
        lev->l.guest_dispatch                   = SLSH_guest_dispatch;
        lev->l.guest_epilogue                   = SLSH_guest_epilogue;
        lev->l.guest_activate                   = SLSH_guest_activate;
        lev->l.guest_insert                     = SLSH_guest_insert;
        lev->l.guest_extract                    = SLSH_guest_extract;
        lev->l.guest_endcycle                   = SLSH_guest_endcycle;
        lev->l.guest_end                        = SLSH_guest_end;
        lev->l.guest_sleep                      = SLSH_guest_sleep;
       
        /* fill the SLSH descriptor part */
        for(i = 0; i < MAX_PROC; i++)
        {
                lev->tasks[i].est = -1;
                lev->tasks[i].dabs = 0;
                lev->tasks[i].interval = -1;
        }
       
        for(i = 0; i < MAX_INTERVALS; i++)
        {
                lev->intervals[i].start = -1;
                lev->intervals[i].end = -1;
                lev->intervals[i].length = 0;
                lev->intervals[i].maxt = 0;
                lev->intervals[i].sc = 0;
        }

        lev->current = 0;
        lev->last = NIL;
        lev->slot = 0;
        lev->slot_length = 0;
        lev->slot_event = -1;
}


void SLSH_set_interval(LEVEL l, int start, int end, int maxt)
{
        SLSH_level_des* lev = (SLSH_level_des *)(level_table[l]);
        static int i = -1;     
       
        i++;
        lev->intervals[i].start = start;
        lev->intervals[i].end = end;
        lev->intervals[i].length = end - start;
        lev->intervals[i].maxt = maxt;
        lev->intervals[i].sc = lev->intervals[i].length - maxt;
       
        lev->last = i;
}

void SLSH_set_variables(LEVEL l, TIME length)
{
        SLSH_level_des* lev = (SLSH_level_des *)(level_table[l]);
               
        lev->slot_length = length;                     
}