source: GPL/alsa-kernel/pci/emu10k1/voice.c@ 18

/*
 *  Copyright (c) by Jaroslav Kysela <perex@suse.cz>
 *                   Creative Labs, Inc.
 *                   Lee Revell <rlrevell@joe-job.com>
 *  Routines for control of EMU10K1 chips - voice manager
 *
 *  Rewrote voice allocator for multichannel support - rlrevell 12/2004
 *
 *  BUGS:
 *    --
 *
 *  TODO:
 *    --
 *
 *   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
 *
 */

#define __NO_VERSION__
#include <sound/driver.h>
#include <linux/time.h>
#include <sound/core.h>
#include <sound/emu10k1.h>

/* Previously the voice allocator started at 0 every time.  The new voice
 * allocator uses a round robin scheme.  The next free voice is tracked in
 * the card record and each allocation begins where the last left off.  The
 * hardware requires stereo interleaved voices be aligned to an even/odd
 * boundary.  For multichannel voice allocation we ensure than the block of
 * voices does not cross the 32 voice boundary.  This simplifies the
 * multichannel support and ensures we can use a single write to the
 * (set|clear)_loop_stop registers.  Otherwise (for example) the voices would
 * get out of sync when pausing/resuming a stream.
 *                                                      --rlrevell
 */

static int voice_alloc(emu10k1_t *emu, emu10k1_voice_type_t type, int number, emu10k1_voice_t **rvoice)
{
    emu10k1_voice_t *voice;
    int i, j, k, first_voice, last_voice, skip;

    *rvoice = NULL;
    first_voice = last_voice = 0;
    for (i = emu->next_free_voice, j = 0; j < NUM_G ; i += number, j += number) {
        // printk("i %d j %d next free %d!\n", i, j, emu->next_free_voice);
        i %= NUM_G;
        /* stereo voices must be even/odd */
        if ((number == 2) && (i % 2)) {
            i++;
            continue;
        }

        /* make sure the block of voices does not cross the 32 voice boundary */
        //if (((i % 32) + number) > 32)
        //      continue;

        skip = 0;
        for (k = 0; k < number; k++) {
            voice = &emu->voices[(i+k) % NUM_G];
            if (voice->use) {
                skip = 1;
            }
        }
        if (!skip) {
            // printk("allocated voice %d\n", i);
            first_voice = i;
            last_voice = (i + number) % NUM_G;
            emu->next_free_voice = last_voice;
            break;
        }
    }

    if (first_voice == last_voice)
        return -ENOMEM;

    for (i=0; i < number; i++) {
        voice = &emu->voices[(first_voice + i) % NUM_G];
        // printk("voice alloc - %i, %i of %i\n", voice->number, idx-first_voice+1, number);
        voice->use = 1;
        switch (type) {
        case EMU10K1_PCM:
            voice->pcm = 1;
            break;
        case EMU10K1_SYNTH:
            voice->synth = 1;
            break;
        case EMU10K1_MIDI:
            voice->midi = 1;
            break;
        case EMU10K1_EFX:
            voice->efx = 1;
            break;
        }
    }
    *rvoice = &emu->voices[first_voice];
    return 0;
}

int snd_emu10k1_voice_alloc(emu10k1_t *emu, emu10k1_voice_type_t type, int number, emu10k1_voice_t **rvoice)
{
    unsigned long flags;
    int result;

    snd_assert(rvoice != NULL, return -EINVAL);
    snd_assert(number, return -EINVAL);

    spin_lock_irqsave(&emu->voice_lock, flags);
    for (;;) {
        result = voice_alloc(emu, type, number, rvoice);
        if (result == 0 || type == EMU10K1_SYNTH || type == EMU10K1_MIDI)
            break;

        /* free a voice from synth */
        if (emu->get_synth_voice) {
            result = emu->get_synth_voice(emu);
            if (result >= 0) {
                emu10k1_voice_t *pvoice = &emu->voices[result];
                pvoice->interrupt = NULL;
                pvoice->use = pvoice->pcm = pvoice->synth = pvoice->midi = pvoice->efx = 0;
                pvoice->epcm = NULL;
            }
        }
        if (result < 0)
            break;
    }
    spin_unlock_irqrestore(&emu->voice_lock, flags);

    return result;
}

int snd_emu10k1_voice_free(emu10k1_t *emu, emu10k1_voice_t *pvoice)
{
    unsigned long flags;

    snd_assert(pvoice != NULL, return -EINVAL);
    spin_lock_irqsave(&emu->voice_lock, flags);
    pvoice->interrupt = NULL;
    pvoice->use = pvoice->pcm = pvoice->synth = pvoice->midi = pvoice->efx = 0;
    pvoice->epcm = NULL;
    snd_emu10k1_voice_init(emu, pvoice->number);
    spin_unlock_irqrestore(&emu->voice_lock, flags);
    return 0;
}