rockbox/firmware/kernel.c

/***************************************************************************
 *             __________               __   ___.
 *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
 *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
 *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
 *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
 *                     \/            \/     \/    \/            \/
 * $Id$
 *
 * Copyright (C) 2002 by Björn Stenberg
 *
 * 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 software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 ****************************************************************************/
#include <stdlib.h>
#include <string.h>
#include "config.h"
#include "kernel.h"
#include "thread.h"
#include "cpu.h"
#include "system.h"
#include "panic.h"
#include "debug.h"
#include "general.h"

/* Make this nonzero to enable more elaborate checks on objects */
#if defined(DEBUG) || defined(SIMULATOR)
#define KERNEL_OBJECT_CHECKS 1 /* Always 1 for DEBUG and sim*/
#else
#define KERNEL_OBJECT_CHECKS 0
#endif

#if KERNEL_OBJECT_CHECKS
#ifdef SIMULATOR
#define KERNEL_ASSERT(exp, msg...) \
    ({ if (!({ exp; })) { DEBUGF(msg); exit(-1); } })
#else
#define KERNEL_ASSERT(exp, msg...) \
    ({ if (!({ exp; })) panicf(msg); })
#endif
#else
#define KERNEL_ASSERT(exp, msg...) ({})
#endif

#if !defined(CPU_PP) || !defined(BOOTLOADER) || \
    defined(HAVE_BOOTLOADER_USB_MODE)
volatile long current_tick SHAREDDATA_ATTR = 0;
#endif

/* Unless otherwise defined, do nothing */
#ifndef YIELD_KERNEL_HOOK
#define YIELD_KERNEL_HOOK() false
#endif
#ifndef SLEEP_KERNEL_HOOK
#define SLEEP_KERNEL_HOOK(ticks) false
#endif

/* List of tick tasks - final element always NULL for termination */
void (*tick_funcs[MAX_NUM_TICK_TASKS+1])(void);

/* This array holds all queues that are initiated. It is used for broadcast. */
static struct
{
    struct event_queue *queues[MAX_NUM_QUEUES+1];
#ifdef HAVE_CORELOCK_OBJECT
    struct corelock cl;
#endif
} all_queues SHAREDBSS_ATTR;

/****************************************************************************
 * Standard kernel stuff
 ****************************************************************************/
void kernel_init(void)
{
    /* Init the threading API */
    init_threads();

    /* Other processors will not reach this point in a multicore build.
     * In a single-core build with multiple cores they fall-through and
     * sleep in cop_main without returning. */
    if (CURRENT_CORE == CPU)
    {
        memset(tick_funcs, 0, sizeof(tick_funcs));
        memset(&all_queues, 0, sizeof(all_queues));
        corelock_init(&all_queues.cl);
        tick_start(1000/HZ);
#ifdef KDEV_INIT
        kernel_device_init();
#endif
    }
}

/****************************************************************************
 * Timer tick - Timer initialization and interrupt handler is defined at
 * the target level.
 ****************************************************************************/
int tick_add_task(void (*f)(void))
{
    int oldlevel = disable_irq_save();
    void **arr = (void **)tick_funcs;
    void **p = find_array_ptr(arr, f);

    /* Add a task if there is room */
    if(p - arr < MAX_NUM_TICK_TASKS)
    {
        *p = f; /* If already in list, no problem. */
    }
    else
    {
        panicf("Error! tick_add_task(): out of tasks");
    }

    restore_irq(oldlevel);
    return 0;
}

int tick_remove_task(void (*f)(void))
{
    int oldlevel = disable_irq_save();
    int rc = remove_array_ptr((void **)tick_funcs, f);
    restore_irq(oldlevel);
    return rc;
}

/****************************************************************************
 * Tick-based interval timers/one-shots - be mindful this is not really
 * intended for continuous timers but for events that need to run for a short
 * time and be cancelled without further software intervention.
 ****************************************************************************/
#ifdef INCLUDE_TIMEOUT_API
/* list of active timeout events */
static struct timeout *tmo_list[MAX_NUM_TIMEOUTS+1];

/* timeout tick task - calls event handlers when they expire
 * Event handlers may alter expiration, callback and data during operation.
 */
static void timeout_tick(void)
{
    unsigned long tick = current_tick;
    struct timeout **p = tmo_list;
    struct timeout *curr;

    for(curr = *p; curr != NULL; curr = *(++p))
    {
        int ticks;

        if(TIME_BEFORE(tick, curr->expires))
            continue;

        /* this event has expired - call callback */
        ticks = curr->callback(curr);
        if(ticks > 0)
        {
            curr->expires = tick + ticks; /* reload */
        }
        else
        {
            timeout_cancel(curr); /* cancel */
        }
    }
}

/* Cancels a timeout callback - can be called from the ISR */
void timeout_cancel(struct timeout *tmo)
{
    int oldlevel = disable_irq_save();
    int rc = remove_array_ptr((void **)tmo_list, tmo);

    if(rc >= 0 && *tmo_list == NULL)
    {
        tick_remove_task(timeout_tick); /* Last one - remove task */
    }

    restore_irq(oldlevel);
}

/* Adds a timeout callback - calling with an active timeout resets the
   interval - can be called from the ISR */
void timeout_register(struct timeout *tmo, timeout_cb_type callback,
                      int ticks, intptr_t data)
{
    int oldlevel;
    void **arr, **p;

    if(tmo == NULL)
        return;

    oldlevel = disable_irq_save();

    /* See if this one is already registered */
    arr = (void **)tmo_list;
    p = find_array_ptr(arr, tmo);

    if(p - arr < MAX_NUM_TIMEOUTS)
    {
        /* Vacancy */
        if(*p == NULL)
        {
            /* Not present */
            if(*tmo_list == NULL)
            {
                tick_add_task(timeout_tick); /* First one - add task */
            }

            *p = tmo;
        }

        tmo->callback = callback;
        tmo->data = data;
        tmo->expires = current_tick + ticks;
    }

    restore_irq(oldlevel);
}

#endif /* INCLUDE_TIMEOUT_API */

/****************************************************************************
 * Thread stuff
 ****************************************************************************/

/* Suspends a thread's execution for at least the specified number of ticks.
 * May result in CPU core entering wait-for-interrupt mode if no other thread
 * may be scheduled.
 *
 * NOTE: sleep(0) sleeps until the end of the current tick
 *       sleep(n) that doesn't result in rescheduling:
 *                      n <= ticks suspended < n + 1
 *       n to n+1 is a lower bound. Other factors may affect the actual time
 *       a thread is suspended before it runs again.
 */
unsigned sleep(unsigned ticks)
{
    /* In certain situations, certain bootloaders in particular, a normal
     * threading call is inappropriate. */
    if (SLEEP_KERNEL_HOOK(ticks))
        return 0; /* Handled */

    disable_irq();
    sleep_thread(ticks);
    switch_thread();
    return 0;
}

/* Elects another thread to run or, if no other thread may be made ready to
 * run, immediately returns control back to the calling thread.
 */
void yield(void)
{
    /* In certain situations, certain bootloaders in particular, a normal
     * threading call is inappropriate. */
    if (YIELD_KERNEL_HOOK())
        return; /* handled */

    switch_thread();
}

/****************************************************************************
 * Queue handling stuff
 ****************************************************************************/

#ifdef HAVE_EXTENDED_MESSAGING_AND_NAME
/****************************************************************************
 * Sender thread queue structure that aids implementation of priority
 * inheritance on queues because the send list structure is the same as
 * for all other kernel objects:
 *
 * Example state:
 * E0 added with queue_send and removed by thread via queue_wait(_w_tmo)
 * E3 was posted with queue_post
 * 4 events remain enqueued (E1-E4)
 *
 *                                 rd                          wr
 * q->events[]:          |  XX  |  E1  |  E2  |  E3  |  E4  |  XX  |
 * q->send->senders[]:   | NULL |  T1  |  T2  | NULL |  T3  | NULL |
 *                                 \/     \/            \/
 * q->send->list:       >->|T0|<->|T1|<->|T2|<-------->|T3|<-<
 * q->send->curr_sender:    /\
 *
 * Thread has E0 in its own struct queue_event.
 *
 ****************************************************************************/

/* Puts the specified return value in the waiting thread's return value
 * and wakes the thread.
 *
 * A sender should be confirmed to exist before calling which makes it
 * more efficent to reject the majority of cases that don't need this
 * called.
 */
static void queue_release_sender(struct thread_entry * volatile * sender,
                                 intptr_t retval)
{
    struct thread_entry *thread = *sender;

    *sender = NULL;               /* Clear slot. */
#ifdef HAVE_WAKEUP_EXT_CB
    thread->wakeup_ext_cb = NULL; /* Clear callback. */
#endif
    thread->retval = retval;      /* Assign thread-local return value. */
    *thread->bqp = thread;        /* Move blocking queue head to thread since
                                     wakeup_thread wakes the first thread in
                                     the list. */
    wakeup_thread(thread->bqp);
}

/* Releases any waiting threads that are queued with queue_send -
 * reply with 0.
 */
static void queue_release_all_senders(struct event_queue *q)
{
    if(q->send)
    {
        unsigned int i;
        for(i = q->read; i != q->write; i++)
        {
            struct thread_entry **spp =
                &q->send->senders[i & QUEUE_LENGTH_MASK];

            if(*spp)
            {
                queue_release_sender(spp, 0);
            }
        }
    }
}

/* Callback to do extra forced removal steps from sender list in addition
 * to the normal blocking queue removal and priority dis-inherit */
static void queue_remove_sender_thread_cb(struct thread_entry *thread)
{
    *((struct thread_entry **)thread->retval) = NULL;
#ifdef HAVE_WAKEUP_EXT_CB
    thread->wakeup_ext_cb = NULL;
#endif
    thread->retval = 0;
}

/* Enables queue_send on the specified queue - caller allocates the extra
 * data structure. Only queues which are taken to be owned by a thread should
 * enable this however an official owner is not compulsory but must be
 * specified for priority inheritance to operate.
 *
 * Use of queue_wait(_w_tmo) by multiple threads on a queue using synchronous
 * messages results in an undefined order of message replies or possible default
 * replies if two or more waits happen before a reply is done.
 */
void queue_enable_queue_send(struct event_queue *q,
                             struct queue_sender_list *send,
                             unsigned int owner_id)
{
    int oldlevel = disable_irq_save();
    corelock_lock(&q->cl);

    if(send != NULL && q->send == NULL)
    {
        memset(send, 0, sizeof(*send));
#ifdef HAVE_PRIORITY_SCHEDULING
        send->blocker.wakeup_protocol = wakeup_priority_protocol_release;
        send->blocker.priority = PRIORITY_IDLE;
        if(owner_id != 0)
        {
            send->blocker.thread = thread_id_entry(owner_id);
            q->blocker_p = &send->blocker;
        }
#endif
        q->send = send;
    }

    corelock_unlock(&q->cl);
    restore_irq(oldlevel);

    (void)owner_id;
}

/* Unblock a blocked thread at a given event index */
static inline void queue_do_unblock_sender(struct queue_sender_list *send,
                                           unsigned int i)
{
    if(send)
    {
        struct thread_entry **spp = &send->senders[i];

        if(UNLIKELY(*spp))
        {
            queue_release_sender(spp, 0);
        }
    }
}

/* Perform the auto-reply sequence */
static inline void queue_do_auto_reply(struct queue_sender_list *send)
{
    if(send && send->curr_sender)
    {
        /* auto-reply */
        queue_release_sender(&send->curr_sender, 0);
    }
}

/* Moves waiting thread's refrence from the senders array to the
 * current_sender which represents the thread waiting for a reponse to the
 * last message removed from the queue. This also protects the thread from
 * being bumped due to overflow which would not be a valid action since its
 * message _is_ being processed at this point. */
static inline void queue_do_fetch_sender(struct queue_sender_list *send,
                                         unsigned int rd)
{
    if(send)
    {
        struct thread_entry **spp = &send->senders[rd];

        if(*spp)
        {
            /* Move thread reference from array to the next thread
               that queue_reply will release */
            send->curr_sender = *spp;
            (*spp)->retval = (intptr_t)spp;
            *spp = NULL;
        }
        /* else message was posted asynchronously with queue_post */
    }
}
#else
/* Empty macros for when synchoronous sending is not made */
#define queue_release_all_senders(q)
#define queue_do_unblock_sender(send, i)
#define queue_do_auto_reply(send)
#define queue_do_fetch_sender(send, rd)
#endif /* HAVE_EXTENDED_MESSAGING_AND_NAME */

/* Queue must not be available for use during this call */
void queue_init(struct event_queue *q, bool register_queue)
{
    int oldlevel = disable_irq_save();

    if(register_queue)
    {
        corelock_lock(&all_queues.cl);
    }

    corelock_init(&q->cl);
    q->queue = NULL;
    /* What garbage is in write is irrelevant because of the masking design-
     * any other functions the empty the queue do this as well so that
     * queue_count and queue_empty return sane values in the case of a
     * concurrent change without locking inside them. */
    q->read = q->write;
#ifdef HAVE_EXTENDED_MESSAGING_AND_NAME
    q->send = NULL; /* No message sending by default */
    IF_PRIO( q->blocker_p = NULL; )
#endif

    if(register_queue)
    {
        void **queues = (void **)all_queues.queues;
        void **p = find_array_ptr(queues, q);

        if(p - queues >= MAX_NUM_QUEUES)
        {
            panicf("queue_init->out of queues");
        }

        if(*p == NULL)
        {
            /* Add it to the all_queues array */
            *p = q;
            corelock_unlock(&all_queues.cl);
        }
    }

    restore_irq(oldlevel);
}

/* Queue must not be available for use during this call */
void queue_delete(struct event_queue *q)
{
    int oldlevel = disable_irq_save();
    corelock_lock(&all_queues.cl);
    corelock_lock(&q->cl);

    /* Remove the queue if registered */
    remove_array_ptr((void **)all_queues.queues, q);

    corelock_unlock(&all_queues.cl);

    /* Release thread(s) waiting on queue head */
    thread_queue_wake(&q->queue);

#ifdef HAVE_EXTENDED_MESSAGING_AND_NAME
    if(q->send)
    {
        /* Release threads waiting for replies */
        queue_release_all_senders(q);

        /* Reply to any dequeued message waiting for one */
        queue_do_auto_reply(q->send);

        q->send = NULL;
        IF_PRIO( q->blocker_p = NULL; )
    }
#endif

    q->read = q->write;

    corelock_unlock(&q->cl);
    restore_irq(oldlevel);
}

/* NOTE: multiple threads waiting on a queue head cannot have a well-
   defined release order if timeouts are used. If multiple threads must
   access the queue head, use a dispatcher or queue_wait only. */
void queue_wait(struct event_queue *q, struct queue_event *ev)
{
    int oldlevel;
    unsigned int rd;

#ifdef HAVE_PRIORITY_SCHEDULING
    KERNEL_ASSERT(QUEUE_GET_THREAD(q) == NULL ||
                  QUEUE_GET_THREAD(q) == thread_self_entry(),
                  "queue_wait->wrong thread\n");
#endif

    oldlevel = disable_irq_save();
    corelock_lock(&q->cl);

#ifdef HAVE_EXTENDED_MESSAGING_AND_NAME
    /* Auto-reply (even if ev is NULL to avoid stalling a waiting thread) */
    queue_do_auto_reply(q->send);
#endif

    while(1)
    {
        struct thread_entry *current;

        rd = q->read;
        if (rd != q->write) /* A waking message could disappear */
            break;

        current = thread_self_entry();

        IF_COP( current->obj_cl = &q->cl; )
        current->bqp = &q->queue;

        block_thread(current);

        corelock_unlock(&q->cl);
        switch_thread();

        disable_irq();
        corelock_lock(&q->cl);
    } 

#ifdef HAVE_EXTENDED_MESSAGING_AND_NAME
    if(ev)
#endif
    {
        q->read = rd + 1;
        rd &= QUEUE_LENGTH_MASK;
        *ev = q->events[rd];

        /* Get data for a waiting thread if one */
        queue_do_fetch_sender(q->send, rd);
    }
    /* else just waiting on non-empty */

    corelock_unlock(&q->cl);
    restore_irq(oldlevel);
}

void queue_wait_w_tmo(struct event_queue *q, struct queue_event *ev, int ticks)
{
    int oldlevel;
    unsigned int rd, wr;

    /* this function works only with a positive number (or zero) of ticks */
    if (ticks == TIMEOUT_BLOCK)
    {
        queue_wait(q, ev);
        return;
    }

#ifdef HAVE_EXTENDED_MESSAGING_AND_NAME
    KERNEL_ASSERT(QUEUE_GET_THREAD(q) == NULL ||
                  QUEUE_GET_THREAD(q) == thread_self_entry(),
                  "queue_wait_w_tmo->wrong thread\n");
#endif

    oldlevel = disable_irq_save();
    corelock_lock(&q->cl);

#ifdef HAVE_EXTENDED_MESSAGING_AND_NAME
    /* Auto-reply (even if ev is NULL to avoid stalling a waiting thread) */
    queue_do_auto_reply(q->send);
#endif

    rd = q->read;
    wr = q->write;
    if (rd == wr && ticks > 0)
    {
        struct thread_entry *current = thread_self_entry();

        IF_COP( current->obj_cl = &q->cl; )
        current->bqp = &q->queue;

        block_thread_w_tmo(current, ticks);
        corelock_unlock(&q->cl);    

        switch_thread();

        disable_irq();
        corelock_lock(&q->cl);

        rd = q->read;
        wr = q->write;
    }

#ifdef HAVE_EXTENDED_MESSAGING_AND_NAME
    if(ev)
#endif
    {
        /* no worry about a removed message here - status is checked inside
           locks - perhaps verify if timeout or false alarm */
        if (rd != wr)
        {
            q->read = rd + 1;
            rd &= QUEUE_LENGTH_MASK;
            *ev = q->events[rd];
            /* Get data for a waiting thread if one */
            queue_do_fetch_sender(q->send, rd);
        }
        else
        {
            ev->id = SYS_TIMEOUT;
        }
    }
    /* else just waiting on non-empty */

    corelock_unlock(&q->cl);
    restore_irq(oldlevel);
}

void queue_post(struct event_queue *q, long id, intptr_t data)
{
    int oldlevel;
    unsigned int wr;

    oldlevel = disable_irq_save();
    corelock_lock(&q->cl);

    wr = q->write++ & QUEUE_LENGTH_MASK;

    KERNEL_ASSERT((q->write - q->read) <= QUEUE_LENGTH,
                  "queue_post ovf q=%08lX", (long)q);

    q->events[wr].id   = id;
    q->events[wr].data = data;

    /* overflow protect - unblock any thread waiting at this index */
    queue_do_unblock_sender(q->send, wr);

    /* Wakeup a waiting thread if any */
    wakeup_thread(&q->queue);

    corelock_unlock(&q->cl);
    restore_irq(oldlevel);
}

#ifdef HAVE_EXTENDED_MESSAGING_AND_NAME
/* IRQ handlers are not allowed use of this function - we only aim to
   protect the queue integrity by turning them off. */
intptr_t queue_send(struct event_queue *q, long id, intptr_t data)
{
    int oldlevel;
    unsigned int wr;

    oldlevel = disable_irq_save();
    corelock_lock(&q->cl);

    wr = q->write++ & QUEUE_LENGTH_MASK;

    KERNEL_ASSERT((q->write - q->read) <= QUEUE_LENGTH,
                  "queue_send ovf q=%08lX", (long)q);

    q->events[wr].id   = id;
    q->events[wr].data = data;
    
    if(LIKELY(q->send))
    {
        struct queue_sender_list *send = q->send;
        struct thread_entry **spp = &send->senders[wr];
        struct thread_entry *current = thread_self_entry();

        if(UNLIKELY(*spp))
        {
            /* overflow protect - unblock any thread waiting at this index */
            queue_release_sender(spp, 0);
        }

        /* Wakeup a waiting thread if any */
        wakeup_thread(&q->queue);

        /* Save thread in slot, add to list and wait for reply */
        *spp = current;
        IF_COP( current->obj_cl = &q->cl; )
        IF_PRIO( current->blocker = q->blocker_p; )
#ifdef HAVE_WAKEUP_EXT_CB
        current->wakeup_ext_cb = queue_remove_sender_thread_cb;
#endif
        current->retval = (intptr_t)spp;
        current->bqp = &send->list;

        block_thread(current);

        corelock_unlock(&q->cl);
        switch_thread();

        return current->retval;
    }

    /* Function as queue_post if sending is not enabled */
    wakeup_thread(&q->queue);

    corelock_unlock(&q->cl);
    restore_irq(oldlevel);
    
    return 0;
}

#if 0 /* not used now but probably will be later */
/* Query if the last message dequeued was added by queue_send or not */
bool queue_in_queue_send(struct event_queue *q)
{
    bool in_send;

#if NUM_CORES > 1
    int oldlevel = disable_irq_save();
    corelock_lock(&q->cl);
#endif

    in_send = q->send && q->send->curr_sender;

#if NUM_CORES > 1
    corelock_unlock(&q->cl);
    restore_irq(oldlevel);
#endif

    return in_send;
}
#endif

/* Replies with retval to the last dequeued message sent with queue_send */
void queue_reply(struct event_queue *q, intptr_t retval)
{
    if(q->send && q->send->curr_sender)
    {
        struct queue_sender_list *sender;

        int oldlevel = disable_irq_save();
        corelock_lock(&q->cl);

        sender = q->send;

        /* Double-check locking */
        if(LIKELY(sender && sender->curr_sender))
            queue_release_sender(&sender->curr_sender, retval);

        corelock_unlock(&q->cl);
        restore_irq(oldlevel);
    }
}
#endif /* HAVE_EXTENDED_MESSAGING_AND_NAME */

#ifdef HAVE_EXTENDED_MESSAGING_AND_NAME
/* Scan the even queue from head to tail, returning any event from the
   filter list that was found, optionally removing the event. If an
   event is returned, synchronous events are handled in the same manner as
   with queue_wait(_w_tmo); if discarded, then as queue_clear.
   If filters are NULL, any event matches. If filters exist, the default
   is to search the full queue depth.
   Earlier filters take precedence.

   Return true if an event was found, false otherwise. */
bool queue_peek_ex(struct event_queue *q, struct queue_event *ev,
                   unsigned int flags, const long (*filters)[2])
{
    bool have_msg;
    unsigned int rd, wr;
    int oldlevel;

    if(LIKELY(q->read == q->write))
        return false; /* Empty: do nothing further */

    have_msg = false;

    oldlevel = disable_irq_save();
    corelock_lock(&q->cl);

    /* Starting at the head, find first match  */
    for(rd = q->read, wr = q->write; rd != wr; rd++)
    {
        struct queue_event *e = &q->events[rd & QUEUE_LENGTH_MASK];

        if(filters)
        {
            /* Have filters - find the first thing that passes */
            const long (* f)[2] = filters;
            const long (* const f_last)[2] =
                &filters[flags & QPEEK_FILTER_COUNT_MASK];
            long id = e->id;

            do
            {
                if(UNLIKELY(id >= (*f)[0] && id <= (*f)[1]))
                    goto passed_filter;
            }
            while(++f <= f_last);

            if(LIKELY(!(flags & QPEEK_FILTER_HEAD_ONLY)))
                continue;   /* No match; test next event */
            else
                break;      /* Only check the head */
        }
        /* else - anything passes */

    passed_filter:

        /* Found a matching event */
        have_msg = true;

        if(ev)
            *ev = *e;       /* Caller wants the event */

        if(flags & QPEEK_REMOVE_EVENTS)
        {
            /* Do event removal */
            unsigned int r = q->read;
            q->read = r + 1; /* Advance head */

            if(ev)
            {
                /* Auto-reply */
                queue_do_auto_reply(q->send);
                /* Get the thread waiting for reply, if any */
                queue_do_fetch_sender(q->send, rd & QUEUE_LENGTH_MASK);
            }
            else
            {
                /* Release any thread waiting on this message */
                queue_do_unblock_sender(q->send, rd & QUEUE_LENGTH_MASK);
            }

            /* Slide messages forward into the gap if not at the head */
            while(rd != r)
            {
                unsigned int dst = rd & QUEUE_LENGTH_MASK;
                unsigned int src = --rd & QUEUE_LENGTH_MASK;

                q->events[dst] = q->events[src];
                /* Keep sender wait list in sync */
                if(q->send)
                    q->send->senders[dst] = q->send->senders[src];
            }
        }

        break;
    }

    corelock_unlock(&q->cl);
    restore_irq(oldlevel);

    return have_msg;
}

bool queue_peek(struct event_queue *q, struct queue_event *ev)
{
    return queue_peek_ex(q, ev, 0, NULL);
}

void queue_remove_from_head(struct event_queue *q, long id)
{
    const long f[2] = { id, id };
    while (queue_peek_ex(q, NULL,
            QPEEK_FILTER_HEAD_ONLY | QPEEK_REMOVE_EVENTS, &f));
}
#else /* !HAVE_EXTENDED_MESSAGING_AND_NAME */
/* The more powerful routines aren't required */
bool queue_peek(struct event_queue *q, struct queue_event *ev)
{
    unsigned int rd;

    if(q->read == q->write)
         return false;

    bool have_msg = false;

    int oldlevel = disable_irq_save();
    corelock_lock(&q->cl);

    rd = q->read;
    if(rd != q->write)
    {
        *ev = q->events[rd & QUEUE_LENGTH_MASK];
        have_msg = true;
    }

    corelock_unlock(&q->cl);
    restore_irq(oldlevel);

    return have_msg;
}

void queue_remove_from_head(struct event_queue *q, long id)
{
    int oldlevel;

    oldlevel = disable_irq_save();
    corelock_lock(&q->cl);

    while(q->read != q->write)
    {
        unsigned int rd = q->read & QUEUE_LENGTH_MASK;

        if(q->events[rd].id != id)
        {
            break;
        }

        /* Release any thread waiting on this message */
        queue_do_unblock_sender(q->send, rd);

        q->read++;
    }

    corelock_unlock(&q->cl);
    restore_irq(oldlevel);
}
#endif /* HAVE_EXTENDED_MESSAGING_AND_NAME */

/* Poll queue to see if a message exists - careful in using the result if
 * queue_remove_from_head is called when messages are posted - possibly use
 * queue_wait_w_tmo(&q, 0) in that case or else a removed message that
 * unsignals the queue may cause an unwanted block */
bool queue_empty(const struct event_queue* q)
{
    return ( q->read == q->write );
}

void queue_clear(struct event_queue* q)
{
    int oldlevel;

    oldlevel = disable_irq_save();
    corelock_lock(&q->cl);

    /* Release all threads waiting in the queue for a reply -
       dequeued sent message will be handled by owning thread */
    queue_release_all_senders(q);

    q->read = q->write;

    corelock_unlock(&q->cl);
    restore_irq(oldlevel);
}

/**
 * The number of events waiting in the queue.
 * 
 * @param struct of event_queue
 * @return number of events in the queue
 */
int queue_count(const struct event_queue *q)
{
    return q->write - q->read;
}

int queue_broadcast(long id, intptr_t data)
{
    struct event_queue **p = all_queues.queues;
    struct event_queue *q;

#if NUM_CORES > 1
    int oldlevel = disable_irq_save();
    corelock_lock(&all_queues.cl);
#endif

    for(q = *p; q != NULL; q = *(++p))
    {
        queue_post(q, id, data);
    }

#if NUM_CORES > 1
    corelock_unlock(&all_queues.cl);
    restore_irq(oldlevel);
#endif
   
    return p - all_queues.queues;
}

/****************************************************************************
 * Simple mutex functions ;)
 ****************************************************************************/

static inline void __attribute__((always_inline))
mutex_set_thread(struct mutex *mtx, struct thread_entry *td)
{
#ifdef HAVE_PRIORITY_SCHEDULING
    mtx->blocker.thread = td;
#else
    mtx->thread = td;
#endif
}

static inline struct thread_entry * __attribute__((always_inline))
mutex_get_thread(volatile struct mutex *mtx)
{
#ifdef HAVE_PRIORITY_SCHEDULING
    return mtx->blocker.thread;
#else
    return mtx->thread;
#endif
}

/* Initialize a mutex object - call before any use and do not call again once
 * the object is available to other threads */
void mutex_init(struct mutex *m)
{
    corelock_init(&m->cl);
    m->queue = NULL;
    m->recursion = 0;
    mutex_set_thread(m, NULL);
#ifdef HAVE_PRIORITY_SCHEDULING
    m->blocker.priority = PRIORITY_IDLE;
    m->blocker.wakeup_protocol = wakeup_priority_protocol_transfer;
    m->no_preempt = false;
#endif
}

/* Gain ownership of a mutex object or block until it becomes free */
void mutex_lock(struct mutex *m)
{
    struct thread_entry *current = thread_self_entry();

    if(current == mutex_get_thread(m))
    {
        /* current thread already owns this mutex */
        m->recursion++;
        return;
    }

    /* lock out other cores */
    corelock_lock(&m->cl);

    /* must read thread again inside cs (a multiprocessor concern really) */
    if(LIKELY(mutex_get_thread(m) == NULL))
    {
        /* lock is open */
        mutex_set_thread(m, current);
        corelock_unlock(&m->cl);
        return;
    }

    /* block until the lock is open... */
    IF_COP( current->obj_cl = &m->cl; )
    IF_PRIO( current->blocker = &m->blocker; )
    current->bqp = &m->queue;

    disable_irq();
    block_thread(current);

    corelock_unlock(&m->cl);

    /* ...and turn control over to next thread */
    switch_thread();
}

/* Release ownership of a mutex object - only owning thread must call this */
void mutex_unlock(struct mutex *m)
{
    /* unlocker not being the owner is an unlocking violation */
    KERNEL_ASSERT(mutex_get_thread(m) == thread_self_entry(),
                  "mutex_unlock->wrong thread (%s != %s)\n",
                  mutex_get_thread(m)->name,
                  thread_self_entry()->name);

    if(m->recursion > 0)
    {
        /* this thread still owns lock */
        m->recursion--;
        return;
    }

    /* lock out other cores */
    corelock_lock(&m->cl);

    /* transfer to next queued thread if any */
    if(LIKELY(m->queue == NULL))
    {
        /* no threads waiting - open the lock */
        mutex_set_thread(m, NULL);
        corelock_unlock(&m->cl);
        return;
    }
    else
    {
        const int oldlevel = disable_irq_save();
        /* Tranfer of owning thread is handled in the wakeup protocol
         * if priorities are enabled otherwise just set it from the
         * queue head. */
        IFN_PRIO( mutex_set_thread(m, m->queue); )
        IF_PRIO( unsigned int result = ) wakeup_thread(&m->queue);
        restore_irq(oldlevel);

        corelock_unlock(&m->cl);

#ifdef HAVE_PRIORITY_SCHEDULING
        if((result & THREAD_SWITCH) && !m->no_preempt)
            switch_thread();
#endif
    }
}

/****************************************************************************
 * Simple semaphore functions ;)
 ****************************************************************************/
#ifdef HAVE_SEMAPHORE_OBJECTS
/* Initialize the semaphore object.
 * max = maximum up count the semaphore may assume (max >= 1)
 * start = initial count of semaphore (0 <= count <= max) */
void semaphore_init(struct semaphore *s, int max, int start)
{
    KERNEL_ASSERT(max > 0 && start >= 0 && start <= max,
                  "semaphore_init->inv arg\n");
    s->queue = NULL;
    s->max = max;
    s->count = start;
    corelock_init(&s->cl);
}

/* Down the semaphore's count or wait for 'timeout' ticks for it to go up if
 * it is already 0. 'timeout' as TIMEOUT_NOBLOCK (0) will not block and may
 * safely be used in an ISR. */
int semaphore_wait(struct semaphore *s, int timeout)
{
    int ret;
    int oldlevel;
    int count;

    oldlevel = disable_irq_save();
    corelock_lock(&s->cl);

    count = s->count;

    if(LIKELY(count > 0))
    {
        /* count is not zero; down it */
        s->count = count - 1;
        ret = OBJ_WAIT_SUCCEEDED;
    }
    else if(timeout == 0)
    {
        /* just polling it */
        ret = OBJ_WAIT_TIMEDOUT;
    }
    else
    {
        /* too many waits - block until count is upped... */
        struct thread_entry * current = thread_self_entry();
        IF_COP( current->obj_cl = &s->cl; )
        current->bqp = &s->queue;
        /* return value will be OBJ_WAIT_SUCCEEDED after wait if wake was
         * explicit in semaphore_release */
        current->retval = OBJ_WAIT_TIMEDOUT;

        if(timeout > 0)
            block_thread_w_tmo(current, timeout); /* ...or timed out... */
        else
            block_thread(current);                /* -timeout = infinite */

        corelock_unlock(&s->cl);

        /* ...and turn control over to next thread */
        switch_thread();

        return current->retval;
    }

    corelock_unlock(&s->cl);
    restore_irq(oldlevel);

    return ret;
}

/* Up the semaphore's count and release any thread waiting at the head of the
 * queue. The count is saturated to the value of the 'max' parameter specified
 * in 'semaphore_init'. */
void semaphore_release(struct semaphore *s)
{
    unsigned int result = THREAD_NONE;
    int oldlevel;

    oldlevel = disable_irq_save();
    corelock_lock(&s->cl);

    if(LIKELY(s->queue != NULL))
    {
        /* a thread was queued - wake it up and keep count at 0 */
        KERNEL_ASSERT(s->count == 0,
            "semaphore_release->threads queued but count=%d!\n", s->count);
        s->queue->retval = OBJ_WAIT_SUCCEEDED; /* indicate explicit wake */
        result = wakeup_thread(&s->queue);
    }
    else
    {
        int count = s->count;
        if(count < s->max)
        {
            /* nothing waiting - up it */
            s->count = count + 1;
        }
    }

    corelock_unlock(&s->cl);
    restore_irq(oldlevel);

#if defined(HAVE_PRIORITY_SCHEDULING) && defined(is_thread_context)
    /* No thread switch if not thread context */
    if((result & THREAD_SWITCH) && is_thread_context())
        switch_thread();
#endif
    (void)result;
}
#endif /* HAVE_SEMAPHORE_OBJECTS */