apps/mpeg.c

/***************************************************************************
 *             __________               __   ___.
 *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
 *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
 *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
 *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
 *                     \/            \/     \/    \/            \/
 * $Id$
 *
 * Copyright (C) 2002 by Linus Nielsen Feltzing
 *
 * 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 <stdbool.h>
#include <stdlib.h>
#include "config.h"

#if CONFIG_CODEC != SWCODEC

#include "debug.h"
#include "panic.h"
#include "metadata.h"
#include "mpeg.h"
#include "audio.h"
#include "storage.h"
#include "string.h"
#include <kernel.h>
#include "thread.h"
#include "errno.h"
#include "mp3data.h"
#include "core_alloc.h"
#include "mp3_playback.h"
#include "talk.h"
#include "sound.h"
#include "system.h"
#include "appevents.h"
#include "playlist.h"
#include "cuesheet.h"
#include "settings.h"
#ifndef SIMULATOR
#include "i2c.h"
#include "mas35xx.h"
#include "system.h"
#include "usb.h"
#include "file.h"
#include "hwcompat.h"
#endif /* !SIMULATOR */
#ifdef HAVE_LCD_BITMAP
#include "lcd.h"
#endif /* CONFIG_CODEC != SWCODEC */

#define MPEG_SWAP_CHUNKSIZE  0x2000
#define MPEG_HIGH_WATER  2 /* We leave 2 bytes empty because otherwise we
                              wouldn't be able to see the difference between
                              an empty buffer and a full one. */
#define MPEG_LOW_WATER                  0x60000
#define MPEG_RECORDING_LOW_WATER        0x80000
#define MPEG_LOW_WATER_CHUNKSIZE        0x40000
#define MPEG_LOW_WATER_SWAP_CHUNKSIZE   0x10000
#if (CONFIG_STORAGE & STORAGE_MMC)
#define MPEG_PLAY_PENDING_THRESHOLD     0x20000
#define MPEG_PLAY_PENDING_SWAPSIZE      0x20000
#else
#define MPEG_PLAY_PENDING_THRESHOLD     0x10000
#define MPEG_PLAY_PENDING_SWAPSIZE      0x10000
#endif

#define MPEG_MAX_PRERECORD_SECONDS 30

/* For ID3 info and VBR header */
#define MPEG_RESERVED_HEADER_SPACE (4096 + 576)

#ifndef SIMULATOR
extern unsigned long mas_version_code;
#endif

#if CONFIG_CODEC == MAS3587F
extern enum /* from mp3_playback.c */
{
    MPEG_DECODER,
    MPEG_ENCODER
} mpeg_mode;
#endif /* CONFIG_CODEC == MAS3587F */

#define MPEG_PLAY                  1
#define MPEG_STOP                  2
#define MPEG_PAUSE                 3
#define MPEG_RESUME                4
#define MPEG_NEXT                  5
#define MPEG_PREV                  6
#define MPEG_FF_REWIND             7
#define MPEG_FLUSH_RELOAD          8
#define MPEG_RECORD                9
#define MPEG_INIT_RECORDING       10
#define MPEG_INIT_PLAYBACK        11
#define MPEG_NEW_FILE             12
#define MPEG_PAUSE_RECORDING      13
#define MPEG_RESUME_RECORDING     14
#define MPEG_NEED_DATA           100
#define MPEG_TRACK_CHANGE        101
#define MPEG_SAVE_DATA           102
#define MPEG_STOP_DONE           103
#define MPEG_PRERECORDING_TICK   104

/* indicator for MPEG_NEED_DATA */
#define GENERATE_UNBUFFER_EVENTS 1

/* list of tracks in memory */
#define MAX_TRACK_ENTRIES (1<<4) /* Must be power of 2 */
#define MAX_TRACK_ENTRIES_MASK (MAX_TRACK_ENTRIES - 1)

struct trackdata
{
    struct mp3entry id3;
    int mempos;
    int load_ahead_index;
};

static struct trackdata trackdata[MAX_TRACK_ENTRIES];

static unsigned int current_track_counter = 0;

#ifndef SIMULATOR
static void stop_playing(void);

static int track_read_idx = 0;
static int track_write_idx = 0;
#endif /* !SIMULATOR */

/* Cuesheet support */
static struct cuesheet *curr_cuesheet = NULL;
static bool checked_for_cuesheet = false;

static const char mpeg_thread_name[] = "mpeg";
static unsigned int audio_thread_id;
static bool audio_is_initialized;
static unsigned int mpeg_errno;

static bool playing = false;    /* We are playing an MP3 stream */
static bool is_playing = false; /* We are (attempting to) playing MP3 files */
static bool paused;             /* playback is paused */
static int audiobuf_handle;     /* handle to the audio buffer */
static char* mpeg_audiobuf;     /* poiunter to the audio buffer */
static long audiobuflen;        /* length of the audio buffer */
#define AUDIO_BUFFER_RESERVE    (256*1024)
#ifdef SIMULATOR
static char mpeg_stack[DEFAULT_STACK_SIZE];
static struct mp3entry taginfo;
#else /* !SIMULATOR */
static struct event_queue mpeg_queue SHAREDBSS_ATTR;
static long mpeg_stack[(DEFAULT_STACK_SIZE + 0x1000)/sizeof(long)];

static int audiobuf_write;
static int audiobuf_swapwrite;
static long audiobuf_read;

static int mpeg_file;

static bool play_pending; /* We are about to start playing */
static bool play_pending_track_change;  /* When starting play we're starting a new file */
static bool filling;      /* We are filling the buffer with data from disk */
static bool dma_underrun; /* True when the DMA has stopped because of
                             slow disk reading (read error, shaking) */
static bool mpeg_stop_done;

static int last_dma_tick = 0;
static int last_dma_chunk_size;

static long low_watermark;          /* Dynamic low watermark level */
static long low_watermark_margin = 0;   /* Extra time in seconds for watermark */
static long lowest_watermark_level; /* Debug value to observe the buffer
                                       usage */

struct audio_resume_info
{
    unsigned long elapsed;
    unsigned long offset;
};

#if CONFIG_CODEC == MAS3587F
static char recording_filename[MAX_PATH]; /* argument to thread */
static char delayed_filename[MAX_PATH];   /* internal copy of above */

static char xing_buffer[MAX_XING_HEADER_SIZE];

static bool init_recording_done;
static bool init_playback_done;
static bool prerecording;        /* True if prerecording is enabled */
static bool is_prerecording;     /* True if we are prerecording */
static bool is_recording;        /* We are recording */

static enum {
    NOT_SAVING = 0,  /* reasons to save data, sorted by importance */
    BUFFER_FULL,
    NEW_FILE,
    STOP_RECORDING
} saving_status;

static int rec_frequency_index; /* For create_xing_header() calls */
static int rec_version_index;   /* For create_xing_header() calls */

struct prerecord_info {
    int mempos;
    unsigned long framecount;
};

static struct prerecord_info prerecord_buffer[MPEG_MAX_PRERECORD_SECONDS];
static int prerecord_index;       /* Current index in the prerecord buffer */
static int prerecording_max_seconds;     /* Max number of seconds to store */
static int prerecord_count;   /* Number of seconds in the prerecord buffer */
static int prerecord_timeout; /* The tick count of the next prerecord data
                                 store */

static unsigned long record_start_time; /* Value of current_tick when recording
                                           was started */
static unsigned long pause_start_time;  /* Value of current_tick when pause was
                                           started */
static unsigned long last_rec_time;
static unsigned long num_rec_bytes;
static unsigned long last_rec_bytes;
static unsigned long frame_count_start;
static unsigned long frame_count_end;
static unsigned long saved_header = 0;

/* Shadow MAS registers */
unsigned long shadow_encoder_control = 0;
#endif /* CONFIG_CODEC == MAS3587F */

#if (CONFIG_CODEC == MAS3587F) || (CONFIG_CODEC == MAS3539F)
unsigned long shadow_io_control_main = 0;
unsigned long shadow_soft_mute = 0;
unsigned shadow_codec_reg0;
#endif /* (CONFIG_CODEC == MAS3587F) || (CONFIG_CODEC == MAS3539F) */

#ifdef HAVE_RECORDING
static const unsigned char empty_id3_header[] =
{
    'I', 'D', '3', 0x03, 0x00, 0x00,
    0x00, 0x00, 0x1f, 0x76 /* Size is 4096 minus 10 bytes for the header */
};
#endif /* HAVE_RECORDING */


static int get_unplayed_space(void);
static int get_playable_space(void);
static int get_unswapped_space(void);
#endif /* !SIMULATOR */

#if (CONFIG_CODEC == MAS3587F) && !defined(SIMULATOR)
static void init_recording(void);
static void prepend_header(void);
static void update_header(void);
static void start_prerecording(void);
static void start_recording(void);
static void stop_recording(void);
static int get_unsaved_space(void);
static void pause_recording(void);
static void resume_recording(void);
#endif /* (CONFIG_CODEC == MAS3587F) && !defined(SIMULATOR) */

static void audio_reset_buffer_noalloc(void* buf, size_t bufsize);
static void audio_reset_buffer(void);


#ifndef SIMULATOR
static int num_tracks_in_memory(void)
{
    return (track_write_idx - track_read_idx) & MAX_TRACK_ENTRIES_MASK;
}

#ifdef DEBUG_TAGS
static void debug_tags(void)
{
    int i;

    for(i = 0;i < MAX_TRACK_ENTRIES;i++)
    {
        DEBUGF("%d - %s\n", i, trackdata[i].id3.path);
    }
    DEBUGF("read: %d, write :%d\n", track_read_idx, track_write_idx);
    DEBUGF("num_tracks_in_memory: %d\n", num_tracks_in_memory());
}
#else /* !DEBUG_TAGS */
#define debug_tags()
#endif /* !DEBUG_TAGS */

static void remove_current_tag(void)
{
    if(num_tracks_in_memory() > 0)
    {
        /* First move the index, so nobody tries to access the tag */
        track_read_idx = (track_read_idx+1) & MAX_TRACK_ENTRIES_MASK;
        checked_for_cuesheet = false;
        debug_tags();
    }
    else
    {
        DEBUGF("remove_current_tag: no tracks to remove\n");
    }
}

static void remove_all_non_current_tags(void)
{
    track_write_idx = (track_read_idx+1) & MAX_TRACK_ENTRIES_MASK;
    debug_tags();
}

static void remove_all_tags(void)
{
    track_write_idx = track_read_idx;

    debug_tags();
}

static struct trackdata *get_trackdata(int offset)
{
    if(offset >= num_tracks_in_memory())
        return NULL;
    else
       return &trackdata[(track_read_idx + offset) & MAX_TRACK_ENTRIES_MASK];
}
#endif /* !SIMULATOR */

/***********************************************************************/
/* audio event handling */

#define MAX_EVENT_HANDLERS 10
struct event_handlers_table
{
    AUDIO_EVENT_HANDLER handler;
    unsigned short mask;
};
static struct event_handlers_table event_handlers[MAX_EVENT_HANDLERS];
static int event_handlers_count = 0;

void audio_register_event_handler(AUDIO_EVENT_HANDLER handler, unsigned short mask)
{
    if (event_handlers_count < MAX_EVENT_HANDLERS)
    {
        event_handlers[event_handlers_count].handler = handler;
        event_handlers[event_handlers_count].mask = mask;
        event_handlers_count++;
    }
}

/* dispatch calls each handler in the order registered and returns after some
   handler actually handles the event (the event is assumed to no longer be valid
   after this, due to the handler changing some condition); returns true if someone
   handled the event, which is expected to cause the caller to skip its own handling
   of the event */
#ifndef SIMULATOR
static bool audio_dispatch_event(unsigned short event, unsigned long data)
{
    int i = 0;
    for(i=0; i < event_handlers_count; i++)
    {
        if ( event_handlers[i].mask & event )
        {
            int rc = event_handlers[i].handler(event, data);
            if ( rc == AUDIO_EVENT_RC_HANDLED )
                return true;
        }
    }
    return false;
}

static void send_track_event(unsigned int id, struct mp3entry *id3)
{
    struct mp3entry *cur_id3 =
        &trackdata[track_read_idx & MAX_TRACK_ENTRIES_MASK].id3;
    unsigned int flags = id3 == cur_id3 ? TEF_CURRENT : 0;
    send_event(id, &(struct track_event){ .flags = flags, .id3 = id3 });
}
#endif /* SIMULATOR */

/***********************************************************************/

static void set_elapsed(struct mp3entry* id3)
{
    if ( id3->vbr ) {
        if ( id3->has_toc ) {
            /* calculate elapsed time using TOC */
            int i;
            unsigned int remainder, plen, relpos, nextpos;

            /* find wich percent we're at */
            for (i=0; i<100; i++ )
            {
                if ( id3->offset < id3->toc[i] * (id3->filesize / 256) )
                {
                    break;
                }
            }

            i--;
            if (i < 0)
                i = 0;

            relpos = id3->toc[i];

            if (i < 99)
            {
                nextpos = id3->toc[i+1];
            }
            else
            {
                nextpos = 256;
            }

            remainder = id3->offset - (relpos * (id3->filesize / 256));

            /* set time for this percent (divide before multiply to prevent
               overflow on long files. loss of precision is negligible on
               short files) */
            id3->elapsed = i * (id3->length / 100);

            /* calculate remainder time */
            plen = (nextpos - relpos) * (id3->filesize / 256);
            id3->elapsed += (((remainder * 100) / plen) *
                             (id3->length / 10000));
        }
        else {
            /* no TOC exists. set a rough estimate using average bitrate */
            int tpk = id3->length / (id3->filesize / 1024);
            id3->elapsed = id3->offset / 1024 * tpk;
        }
    }
    else
        /* constant bitrate, use exact calculation */
        id3->elapsed = id3->offset / (id3->bitrate / 8);
}

static int audio_get_file_pos_int(struct mp3entry *id3)
{
    int pos = -1;

    if (id3->vbr)
    {
        if (id3->has_toc)
        {
            /* Use the TOC to find the new position */
            unsigned int percent, remainder;
            int curtoc, nexttoc, plen;

            percent = (id3->elapsed*100)/id3->length;
            if (percent > 99)
                percent = 99;

            curtoc = id3->toc[percent];

            if (percent < 99)
                nexttoc = id3->toc[percent+1];
            else
                nexttoc = 256;

            pos = (id3->filesize/256)*curtoc;

            /* Use the remainder to get a more accurate position */
            remainder   = (id3->elapsed*100)%id3->length;
            remainder   = (remainder*100)/id3->length;
            plen        = (nexttoc - curtoc)*(id3->filesize/256);
            pos     += (plen/100)*remainder;
        }
        else
        {
            /* No TOC exists, estimate the new position */
            pos = (id3->filesize / (id3->length / 1000)) *
                (id3->elapsed / 1000);
        }
    }
    else if (id3->bitrate)
        pos = id3->elapsed * (id3->bitrate / 8);
    else
    {
        return -1;
    }

    if (pos >= (int)(id3->filesize - id3->id3v1len))
    {
        /* Don't seek right to the end of the file so that we can
           transition properly to the next song */
        pos = id3->filesize - id3->id3v1len - 1;
    }
    else if (pos < (int)id3->first_frame_offset)
    {
        /* skip past id3v2 tag and other leading garbage */
        pos = id3->first_frame_offset;
    }
    return pos;
}

int audio_get_file_pos(void)
{
    struct mp3entry *id3 = audio_current_track();
    return id3 ? audio_get_file_pos_int(id3) : 0;
}

unsigned long mpeg_get_last_header(void)
{
#ifdef SIMULATOR
    return 0;
#else /* !SIMULATOR */
    unsigned long tmp[2];

    /* Read the frame data from the MAS and reconstruct it with the
       frame sync and all */
    mas_readmem(MAS_BANK_D0, MAS_D0_MPEG_STATUS_1, tmp, 2);
    return 0xffe00000 | ((tmp[0] & 0x7c00) << 6) | (tmp[1] & 0xffff);
#endif /* !SIMULATOR */
}

static void do_stop(void)
{
    is_playing = false;
    paused = false;

#ifndef SIMULATOR
    if (playing)
        playlist_update_resume_info(audio_current_track());

    stop_playing();
    mpeg_stop_done = true;
#else
    playing = false;
#endif
}

/* Buffer must not move. */
static int shrink_callback(int handle, unsigned hints, void* start, size_t old_size)
{
    ssize_t extradata_size = old_size - audiobuflen;
    /* check what buflib requests */
    size_t wanted_size = (hints & BUFLIB_SHRINK_SIZE_MASK);
    ssize_t size = (ssize_t)old_size - wanted_size;

#if !defined(SIMULATOR) && (CONFIG_CODEC == MAS3587F)
    /* FIXME: Cannot give the buffer during recording yet */
    if (is_recording)
        return BUFLIB_CB_CANNOT_SHRINK;
#endif

    /* keep at least 256K for the buffering */
    if ((size - extradata_size) < AUDIO_BUFFER_RESERVE)
    {
        /* check if buflib needs the memory really hard. if yes we give
         * up playback for now, otherwise refuse to shrink to keep at least
         * 256K for the buffering */
        if ((hints & BUFLIB_SHRINK_POS_MASK) != BUFLIB_SHRINK_POS_MASK)
            return BUFLIB_CB_CANNOT_SHRINK;
    }
    /* TODO: Do it without stopping playback, if possible */
    bool playing = (audio_status() & AUDIO_STATUS_PLAY) == AUDIO_STATUS_PLAY;
    struct mp3entry *id3 = audio_current_track();
    unsigned long elapsed = 0, offset = 0;
    if (id3)
    {
        elapsed = id3->elapsed;
        offset  = id3->offset;
    }
    /* don't call audio_hard_stop() as it frees this handle */
    if (thread_self() == audio_thread_id)
    {   /* inline case MPEG_STOP (audio_stop()) response
         * if we're in the audio thread since audio_stop() otherwise deadlocks */
        do_stop();
    }
    else
        audio_stop();

    switch (hints & BUFLIB_SHRINK_POS_MASK)
    {
        case BUFLIB_SHRINK_POS_BACK:
            core_shrink(handle, start, size);
            audio_reset_buffer_noalloc(start, size);
            break;
        case BUFLIB_SHRINK_POS_FRONT:
            core_shrink(handle, start + wanted_size, size);
            audio_reset_buffer_noalloc(start + wanted_size, size);
            break;
        case BUFLIB_SHRINK_POS_MASK:
            audiobuf_handle = core_free(audiobuf_handle);
            mpeg_audiobuf = NULL;
            talk_buffer_set_policy(TALK_BUFFER_DEFAULT);
            playing = false;
            break;
    }
    if (playing)
    {   /* safe to call even from the audio thread (due to queue_post()) */
        audio_play(elapsed, offset);
    }

    return BUFLIB_CB_OK;
}

static struct buflib_callbacks ops = {
    .move_callback = NULL,
    .shrink_callback = shrink_callback,
};

#ifndef SIMULATOR
/* Send callback events to notify about removing old tracks. */
static void generate_unbuffer_events(void)
{
    int i;
    int numentries = MAX_TRACK_ENTRIES - num_tracks_in_memory();
    int cur_idx = track_write_idx;

    for (i = 0; i < numentries; i++)
    {
        /* Send an event to notify that track has finished. */
        send_track_event(PLAYBACK_EVENT_TRACK_FINISH, &trackdata[cur_idx].id3);
        cur_idx = (cur_idx + 1) & MAX_TRACK_ENTRIES_MASK;
    }
}

/* Send callback events to notify about new tracks. */
static void generate_postbuffer_events(void)
{
    int i;
    int numentries = num_tracks_in_memory();
    int cur_idx = track_read_idx;

    for (i = 0; i < numentries; i++)
    {
        send_track_event(PLAYBACK_EVENT_TRACK_BUFFER, &trackdata[cur_idx].id3);
        cur_idx = (cur_idx + 1) & MAX_TRACK_ENTRIES_MASK;
    }
}

static void recalculate_watermark(int bitrate)
{
    int bytes_per_sec;
    int time = storage_spinup_time();

    /* A bitrate of 0 probably means empty VBR header. We play safe
       and set a high threshold */
    if(bitrate == 0)
        bitrate = 320;

    bytes_per_sec = bitrate * 1000 / 8;

    if(time)
    {
        /* No drive spins up faster than 3.5s */
        if(time < 350)
            time = 350;

        time = time * 3;
        low_watermark = ((low_watermark_margin * HZ + time) *
                         bytes_per_sec) / HZ;
    }
    else
    {
        low_watermark = MPEG_LOW_WATER;
    }
}

#ifdef HAVE_DISK_STORAGE
void audio_set_buffer_margin(int setting)
{
    low_watermark_margin = setting;     /* in seconds */
}
#endif

void audio_get_debugdata(struct audio_debug *dbgdata)
{
    dbgdata->audiobuflen = audiobuflen;
    dbgdata->audiobuf_write = audiobuf_write;
    dbgdata->audiobuf_swapwrite = audiobuf_swapwrite;
    dbgdata->audiobuf_read = audiobuf_read;

    dbgdata->last_dma_chunk_size = last_dma_chunk_size;

#if CONFIG_CPU == SH7034
    dbgdata->dma_on = (SCR0 & 0x80) != 0;
#endif
    dbgdata->playing = playing;
    dbgdata->play_pending = play_pending;
    dbgdata->is_playing = is_playing;
    dbgdata->filling = filling;
    dbgdata->dma_underrun = dma_underrun;

    dbgdata->unplayed_space = get_unplayed_space();
    dbgdata->playable_space = get_playable_space();
    dbgdata->unswapped_space = get_unswapped_space();

    dbgdata->low_watermark_level = low_watermark;
    dbgdata->lowest_watermark_level = lowest_watermark_level;
}

#ifdef DEBUG
static void dbg_timer_start(void)
{
    /* We are using timer 2 */

    TSTR &= ~0x04; /* Stop the timer */
    TSNC &= ~0x04; /* No synchronization */
    TMDR &= ~0x44; /* Operate normally */

    TCNT2 = 0;   /* Start counting at 0 */
    TCR2 = 0x03; /* Sysclock/8 */

    TSTR |= 0x04; /* Start timer 2 */
}

static int dbg_cnt2us(unsigned int cnt)
{
    return (cnt * 10000) / (FREQ/800);
}
#endif /* DEBUG */

static int get_unplayed_space(void)
{
    int space = audiobuf_write - audiobuf_read;
    if (space < 0)
        space += audiobuflen;
    return space;
}

static int get_playable_space(void)
{
    int space = audiobuf_swapwrite - audiobuf_read;
    if (space < 0)
        space += audiobuflen;
    return space;
}

static int get_unplayed_space_current_song(void)
{
    int space;

    if (num_tracks_in_memory() > 1)
    {
        space = get_trackdata(1)->mempos - audiobuf_read;
    }
    else
    {
        space = audiobuf_write - audiobuf_read;
    }

    if (space < 0)
        space += audiobuflen;

    return space;
}

static int get_unswapped_space(void)
{
    int space = audiobuf_write - audiobuf_swapwrite;
    if (space < 0)
        space += audiobuflen;
    return space;
}

#if CONFIG_CODEC == MAS3587F
static int get_unsaved_space(void)
{
    int space = audiobuf_write - audiobuf_read;
    if (space < 0)
        space += audiobuflen;
    return space;
}

static void drain_dma_buffer(void)
{
    while (PBDRH & 0x40)
    {
        xor_b(0x08, &PADRH);

        while (PBDRH & 0x80);

        xor_b(0x08, &PADRH);

        while (!(PBDRH & 0x80));
    }
}

#ifdef DEBUG
static long timing_info_index = 0;
static long timing_info[1024];
#endif /* DEBUG */

void rec_tick (void) __attribute__ ((section (".icode")));
void rec_tick(void)
{
    int i;
    int delay;
    char data;

    if(is_recording && (PBDRH & 0x40))
    {
#ifdef DEBUG
        timing_info[timing_info_index++] = current_tick;
        TCNT2 = 0;
#endif /* DEBUG */
        /* Note: Although this loop is run in interrupt context, further
         * optimisation will do no good. The MAS would then deliver bad
         * frames occasionally, as observed in extended experiments. */
        i = 0;
        while (PBDRH & 0x40)      /* We try to read as long as EOD is high */
        {
            xor_b(0x08, &PADRH);  /* Set PR active, independent of polarity */

            delay = 100;
            while (PBDRH & 0x80)  /* Wait until /RTW becomes active */
            {
                if (--delay <= 0) /* Bail out if we have to wait too long */
                {                 /* i.e. the MAS doesn't want to talk to us */
                    xor_b(0x08, &PADRH);         /* Set PR inactive */
                    goto transfer_end;           /* and get out of here */
                }
            }

            data = *(unsigned char *)0x04000000; /* read data byte */

            xor_b(0x08, &PADRH);                 /* Set PR inactive */

            mpeg_audiobuf[audiobuf_write++] = data;

            if (audiobuf_write >= audiobuflen)
                audiobuf_write = 0;

            i++;
        }
      transfer_end:

#ifdef DEBUG
        timing_info[timing_info_index++] = TCNT2 + (i << 16);
        timing_info_index &= 0x3ff;
#endif /* DEBUG */

        num_rec_bytes += i;

        if(is_prerecording)
        {
            if(TIME_AFTER(current_tick, prerecord_timeout))
            {
                prerecord_timeout = current_tick + HZ;
                queue_post(&mpeg_queue, MPEG_PRERECORDING_TICK, 0);
            }
        }
        else
        {
            /* Signal to save the data if we are running out of buffer
               space */
            if (audiobuflen - get_unsaved_space() < MPEG_RECORDING_LOW_WATER
                && saving_status == NOT_SAVING)
            {
                saving_status = BUFFER_FULL;
                queue_post(&mpeg_queue, MPEG_SAVE_DATA, 0);
            }
        }
    }
}
#endif /* CONFIG_CODEC == MAS3587F */

void playback_tick(void)
{
    struct trackdata *ptd = get_trackdata(0);
    if(ptd)
    {
        ptd->id3.elapsed += (current_tick - last_dma_tick) * 1000 / HZ;
        last_dma_tick = current_tick;
        audio_dispatch_event(AUDIO_EVENT_POS_REPORT,
                             (unsigned long)ptd->id3.elapsed);
    }
}

static void reset_mp3_buffer(void)
{
    audiobuf_read = 0;
    audiobuf_write = 0;
    audiobuf_swapwrite = 0;
    lowest_watermark_level = audiobuflen;
}

 /* DMA transfer end interrupt callback */
static void transfer_end(const void** ppbuf, size_t* psize)
{
    if(playing && !paused)
    {
        int unplayed_space_left;
        int space_until_end_of_buffer;
        int track_offset = 1;
        struct trackdata *track;

        audiobuf_read += last_dma_chunk_size;
        if(audiobuf_read >= audiobuflen)
            audiobuf_read = 0;

        /* First, check if we are on a track boundary */
        if (num_tracks_in_memory() > 1)
        {
            if (audiobuf_read == get_trackdata(track_offset)->mempos)
            {
                if ( ! audio_dispatch_event(AUDIO_EVENT_END_OF_TRACK, 0) )
                {
                    queue_post(&mpeg_queue, MPEG_TRACK_CHANGE, 0);
                    track_offset++;
                }
            }
        }

        unplayed_space_left = get_unplayed_space();

        space_until_end_of_buffer = audiobuflen - audiobuf_read;

        if(!filling && unplayed_space_left < low_watermark)
        {
            filling = true;
            queue_post(&mpeg_queue, MPEG_NEED_DATA, GENERATE_UNBUFFER_EVENTS);
        }

        if(unplayed_space_left)
        {
            last_dma_chunk_size = MIN(0x2000, unplayed_space_left);
            last_dma_chunk_size = MIN(last_dma_chunk_size,
                                      space_until_end_of_buffer);

            /* several tracks loaded? */
            track = get_trackdata(track_offset);
            if(track)
            {
                /* will we move across the track boundary? */
                if (( audiobuf_read < track->mempos ) &&
                    ((audiobuf_read+last_dma_chunk_size) >
                     track->mempos ))
                {
                    /* Make sure that we end exactly on the boundary */
                    last_dma_chunk_size = track->mempos - audiobuf_read;
                }
            }

            *psize = last_dma_chunk_size & 0xffff;
            *ppbuf = mpeg_audiobuf + audiobuf_read;
            track = get_trackdata(0);
            if(track)
                track->id3.offset += last_dma_chunk_size;

            /* Update the watermark debug level */
            if(unplayed_space_left < lowest_watermark_level)
                lowest_watermark_level = unplayed_space_left;
        }
        else
        {
            /* Check if the end of data is because of a hard disk error.
               If there is an open file handle, we are still playing music.
               If not, the last file has been loaded, and the file handle is
               closed. */
            if(mpeg_file >= 0)
            {
                /* Update the watermark debug level */
                if(unplayed_space_left < lowest_watermark_level)
                    lowest_watermark_level = unplayed_space_left;

                DEBUGF("DMA underrun.\n");
                dma_underrun = true;
            }
            else
            {
                if ( ! audio_dispatch_event(AUDIO_EVENT_END_OF_TRACK, 0) )
                {
                    DEBUGF("No more MP3 data. Stopping.\n");
                    queue_post(&mpeg_queue, MPEG_TRACK_CHANGE, 0);
                    playing = false;
                }
            }
            *psize = 0; /* no more transfer */
        }
    }
}

static struct trackdata *add_track_to_tag_list(const char *filename)
{
    struct trackdata *track;
    bool send_nid3_event;

    if(num_tracks_in_memory() >= MAX_TRACK_ENTRIES)
    {
        DEBUGF("Tag memory is full\n");
        return NULL;
    }

    track = &trackdata[track_write_idx];

    /* grab id3 tag of new file and
       remember where in memory it starts */
    if(mp3info(&track->id3, filename))
    {
        DEBUGF("Bad mp3\n");
        return NULL;
    }
    track->mempos = audiobuf_write;
    track->id3.elapsed = 0;
#ifdef HAVE_LCD_BITMAP
    if (track->id3.title)
        lcd_getstringsize(track->id3.title, NULL, NULL);
    if (track->id3.artist)
        lcd_getstringsize(track->id3.artist, NULL, NULL);
    if (track->id3.album)
        lcd_getstringsize(track->id3.album, NULL, NULL);
#endif

    /* if this track is the next track then let the UI know it can get it */
    send_nid3_event = (track_write_idx == track_read_idx + 1);
    track_write_idx = (track_write_idx+1) & MAX_TRACK_ENTRIES_MASK;
    if (send_nid3_event)
        send_track_event(PLAYBACK_EVENT_NEXTTRACKID3_AVAILABLE, &track->id3);
    debug_tags();
    return track;
}

static int new_file(int steps)
{
    int max_steps = playlist_amount();
    int start = 0;
    int i;
    struct trackdata *track;
    char name_buf[MAX_PATH+1];
    const char *trackname;

    /* Find out how many steps to advance. The load_ahead_index field tells
       us how many playlist entries it had to skip to get to a valid one.
       We add those together to find out where to start. */
    if(steps > 0 && num_tracks_in_memory() > 1)
    {
        /* Begin with the song after the currently playing one */
        i = 1;
        while((track = get_trackdata(i++)))
        {
            start += track->load_ahead_index;
        }
    }

    do {
        trackname = playlist_peek(start + steps, name_buf, sizeof(name_buf));
        if ( !trackname )
            return -1;

        DEBUGF("Loading %s\n", trackname);

        mpeg_file = open(trackname, O_RDONLY);
        if(mpeg_file < 0) {
            DEBUGF("Couldn't open file: %s\n",trackname);
            if(steps < 0)
               steps--;
            else
               steps++;
        }
        else
        {
            struct trackdata *track = add_track_to_tag_list(trackname);

            if(!track)
            {
                /* Bad mp3 file */
                if(steps < 0)
                    steps--;
                else
                    steps++;
                close(mpeg_file);
                mpeg_file = -1;
            }
            else
            {
                /* skip past id3v2 tag */
                lseek(mpeg_file,
                      track->id3.first_frame_offset,
                      SEEK_SET);
                track->id3.index = steps;
                track->load_ahead_index = steps;
                track->id3.offset = 0;

                if(track->id3.vbr)
                    /* Average bitrate * 1.5 */
                    recalculate_watermark(
                        (track->id3.bitrate * 3) / 2);
                else
                    recalculate_watermark(
                        track->id3.bitrate);

            }
        }

        /* Bail out if no file could be opened */
        if(abs(steps) > max_steps)
           return -1;
    } while ( mpeg_file < 0 );

    return 0;
}

static void stop_playing(void)
{
    /* Stop the current stream */
    mp3_play_stop();
    playing = false;
    filling = false;

    if(mpeg_file >= 0)
        close(mpeg_file);
    mpeg_file = -1;
    remove_all_tags();
    generate_unbuffer_events();
    reset_mp3_buffer();
}

static void end_current_track(void)
{
    play_pending = false;
    playing = false;
    mp3_play_pause(false);

    reset_mp3_buffer();
    remove_all_tags();
    generate_unbuffer_events();

    if(mpeg_file >= 0)
        close(mpeg_file);
}

/* Is this a really the end of playback or is a new playlist starting */
static void check_playlist_end(int direction)
{
    /* Use the largest possible step size to account for skipped tracks */
    int steps = playlist_amount();

    if (direction < 0)
        steps = -steps;

    if (playlist_next(steps) < 0)
        is_playing = false;
}

static void update_playlist(void)
{
    if (num_tracks_in_memory() > 0)
    {
        struct trackdata *track = get_trackdata(0);
        track->id3.index = playlist_next(track->id3.index);
    }
    else
    {
        /* End of playlist? */
        check_playlist_end(1);
    }

    playlist_update_resume_info(audio_current_track());
}

static void track_change(void)
{
    DEBUGF("Track change\n");

#if (CONFIG_CODEC == MAS3587F) || (CONFIG_CODEC == MAS3539F)
    /* Reset the AVC */
    sound_set_avc(-1);
#endif /* (CONFIG_CODEC == MAS3587F) || (CONFIG_CODEC == MAS3539F) */

    if (num_tracks_in_memory() > 0)
    {
        remove_current_tag();
        update_playlist();
        if (is_playing)
        {
            send_track_event(PLAYBACK_EVENT_TRACK_CHANGE,
                             audio_current_track());
        }
    }

    current_track_counter++;
}

#ifdef DEBUG
void hexdump(const unsigned char *buf, int len)
{
    int i;

    for(i = 0;i < len;i++)
    {
        if(i && (i & 15) == 0)
        {
            DEBUGF("\n");
        }
        DEBUGF("%02x ", buf[i]);
    }
    DEBUGF("\n");
}
#endif /* DEBUG */

static void start_playback_if_ready(void)
{
    int playable_space;

    playable_space = audiobuf_swapwrite - audiobuf_read;
    if(playable_space < 0)
        playable_space += audiobuflen;

    /* See if we have started playing yet. If not, do it. */
    if(play_pending || dma_underrun)
    {
        /* If the filling has stopped, and we still haven't reached
           the watermark, the file must be smaller than the
           watermark. We must still play it. */
        if((playable_space >= MPEG_PLAY_PENDING_THRESHOLD) ||
           !filling || dma_underrun)
        {
            DEBUGF("P\n");
            if (play_pending) /* don't do this when recovering from DMA underrun */
            {
                generate_postbuffer_events(); /* signal first track as buffered */
                if (play_pending_track_change)
                {
                    play_pending_track_change = false;
                    send_track_event(PLAYBACK_EVENT_TRACK_CHANGE,
                                     audio_current_track());
                }
                play_pending = false;
            }
            playing = true;

            last_dma_chunk_size = MIN(0x2000, get_unplayed_space_current_song());
            mp3_play_data(mpeg_audiobuf + audiobuf_read, last_dma_chunk_size, transfer_end);
            dma_underrun = false;

            if (!paused)
            {
                last_dma_tick = current_tick;
                mp3_play_pause(true);
            }

            /* Tell ourselves that we need more data */
            queue_post(&mpeg_queue, MPEG_NEED_DATA, 0);
        }
    }
}

static bool swap_one_chunk(void)
{
    int free_space_left;
    int amount_to_swap;

    free_space_left = get_unswapped_space();

    if(free_space_left == 0 && !play_pending)
        return false;

    /* Swap in larger chunks when the user is waiting for the playback
       to start, or when there is dangerously little playable data left */
    if(play_pending)
        amount_to_swap = MIN(MPEG_PLAY_PENDING_SWAPSIZE, free_space_left);
    else
    {
        if(get_playable_space() < low_watermark)
            amount_to_swap = MIN(MPEG_LOW_WATER_SWAP_CHUNKSIZE,
                                 free_space_left);
        else
            amount_to_swap = MIN(MPEG_SWAP_CHUNKSIZE, free_space_left);
    }

    if(audiobuf_write < audiobuf_swapwrite)
        amount_to_swap = MIN(audiobuflen - audiobuf_swapwrite,
                             amount_to_swap);
    else
        amount_to_swap = MIN(audiobuf_write - audiobuf_swapwrite,
                             amount_to_swap);

    bitswap(mpeg_audiobuf + audiobuf_swapwrite, amount_to_swap);

    audiobuf_swapwrite += amount_to_swap;
    if(audiobuf_swapwrite >= audiobuflen)
    {
        audiobuf_swapwrite = 0;
    }

    return true;
}

static void mpeg_thread(void)
{
    static int pause_tick = 0;
    static unsigned int pause_track = 0;
    struct queue_event ev;
    int len;
    int free_space_left;
    int unplayed_space_left;
    int amount_to_read;
    int t1, t2;
    unsigned long start_elapsed, start_offset;
#if CONFIG_CODEC == MAS3587F
    int amount_to_save;
    int save_endpos = 0;
    int rc;
    int level;
    long offset;
#endif /* CONFIG_CODEC == MAS3587F */

    is_playing = false;
    play_pending = false;
    playing = false;
    mpeg_file = -1;

    while(1)
    {
#if CONFIG_CODEC == MAS3587F
        if(mpeg_mode == MPEG_DECODER)
        {
#endif /* CONFIG_CODEC == MAS3587F */
        yield();

        /* Swap if necessary, and don't block on the queue_wait() */
        if(swap_one_chunk())
        {
            queue_wait_w_tmo(&mpeg_queue, &ev, 0);
        }
        else if (playing)
        {
            /* periodically update resume info */
            queue_wait_w_tmo(&mpeg_queue, &ev, HZ/2);
        }
        else
        {
            DEBUGF("S R:%x W:%x SW:%x\n",
                   audiobuf_read, audiobuf_write, audiobuf_swapwrite);
            queue_wait(&mpeg_queue, &ev);
        }

        start_playback_if_ready();

        switch(ev.id)
        {
            case MPEG_PLAY:
                DEBUGF("MPEG_PLAY\n");

#if CONFIG_TUNER
                /* Silence the A/D input, it may be on because the radio
                   may be playing */
                mas_codec_writereg(6, 0x0000);
#endif /* CONFIG_TUNER */

                /* Stop the current stream */
                paused = false;
                end_current_track();

                if ( new_file(0) == -1 )
                {
                    is_playing = false;
                    track_change();
                    break;
                }

                start_elapsed = ((struct audio_resume_info *)ev.data)->elapsed;
                start_offset = ((struct audio_resume_info *)ev.data)->offset;

                /* mid-song resume? */
                if (!start_offset && start_elapsed) {
                    struct mp3entry *id3 = &get_trackdata(0)->id3;
                    id3->elapsed = start_elapsed;
                    start_offset = audio_get_file_pos_int(id3);
                }

                if (start_offset) {
                    struct mp3entry* id3 = &get_trackdata(0)->id3;
                    lseek(mpeg_file, start_offset, SEEK_SET);
                    id3->offset = start_offset;
                    set_elapsed(id3);
                }
                else {
                    /* skip past id3v2 tag */
                    lseek(mpeg_file,
                          get_trackdata(0)->id3.first_frame_offset,
                          SEEK_SET);

                }

                /* Make it read more data */
                filling = true;
                queue_post(&mpeg_queue, MPEG_NEED_DATA, 0);

                /* Tell the file loading code that we want to start playing
                   as soon as we have some data */
                play_pending = true;
                play_pending_track_change = true;

                update_playlist();
                current_track_counter++;
                break;

            case MPEG_STOP:
                do_stop();
                break;

            case MPEG_PAUSE:
                DEBUGF("MPEG_PAUSE\n");
                /* Stop the current stream */
                if (playing)
                    playlist_update_resume_info(audio_current_track());
                paused = true;
                playing = false;
                pause_tick = current_tick;
                pause_track = current_track_counter;
                mp3_play_pause(false);
                break;

            case MPEG_RESUME:
                DEBUGF("MPEG_RESUME\n");
                /* Continue the current stream */
                paused = false;
                if (!play_pending)
                {
                    playing = true;
                    if ( current_track_counter == pause_track )
                        last_dma_tick += current_tick - pause_tick;
                    else
                        last_dma_tick = current_tick;
                    pause_tick = 0;
                    mp3_play_pause(true);
                }
                break;

            case MPEG_NEXT:
                DEBUGF("MPEG_NEXT\n");
                /* is next track in ram? */
                if ( num_tracks_in_memory() > 1 ) {
                    int unplayed_space_left, unswapped_space_left;

                    /* stop the current stream */
                    play_pending = false;
                    playing = false;
                    mp3_play_pause(false);

                    track_change();
                    audiobuf_read = get_trackdata(0)->mempos;
                    last_dma_chunk_size = MIN(0x2000, get_unplayed_space_current_song());
                    mp3_play_data(mpeg_audiobuf + audiobuf_read, last_dma_chunk_size, transfer_end);
                    dma_underrun = false;
                    last_dma_tick = current_tick;

                    unplayed_space_left  = get_unplayed_space();
                    unswapped_space_left = get_unswapped_space();

                    /* should we start reading more data? */
                    if(!filling && (unplayed_space_left < low_watermark)) {
                        filling = true;
                        queue_post(&mpeg_queue, MPEG_NEED_DATA, GENERATE_UNBUFFER_EVENTS);
                        play_pending = true;
                    } else if(unswapped_space_left &&
                              unswapped_space_left > unplayed_space_left) {
                        /* Stop swapping the data from the previous file */
                        audiobuf_swapwrite = audiobuf_read;
                        play_pending = true;
                    } else {
                        playing = true;
                        if (!paused)
                            mp3_play_pause(true);
                    }
                }
                else {
                    if (!playlist_check(1))
                        break;

                    /* stop the current stream */
                    end_current_track();

                    if (new_file(1) < 0) {
                        DEBUGF("No more files to play\n");
                        filling = false;

                        check_playlist_end(1);
                        current_track_counter++;
                    } else {
                        /* Make it read more data */
                        filling = true;
                        queue_post(&mpeg_queue, MPEG_NEED_DATA, 0);

                        /* Tell the file loading code that we want
                           to start playing as soon as we have some data */
                        play_pending = true;
                        play_pending_track_change = true;

                        update_playlist();
                        current_track_counter++;
                    }
                }
                break;

            case MPEG_PREV: {
                DEBUGF("MPEG_PREV\n");

                if (!playlist_check(-1))
                    break;

                /* stop the current stream */
                end_current_track();

                /* Open the next file */
                if (new_file(-1) < 0) {
                    DEBUGF("No more files to play\n");
                    filling = false;

                    check_playlist_end(-1);
                    current_track_counter++;
                } else {
                    /* Make it read more data */
                    filling = true;
                    queue_post(&mpeg_queue, MPEG_NEED_DATA, 0);

                    /* Tell the file loading code that we want to
                       start playing as soon as we have some data */
                    play_pending = true;
                    play_pending_track_change = true;

                    update_playlist();
                    current_track_counter++;
                }
                break;
            }

            case MPEG_FF_REWIND: {
                struct mp3entry *id3  = audio_current_track();
                unsigned int oldtime  = id3->elapsed;
                unsigned int newtime  = (unsigned int)ev.data;
                int curpos, newpos, diffpos;
                DEBUGF("MPEG_FF_REWIND\n");

                id3->elapsed = newtime;

                newpos = audio_get_file_pos_int(id3);
                if(newpos < 0)
                {
                    id3->elapsed = oldtime;
                    break;
                }

                if (mpeg_file >= 0)
                    curpos = lseek(mpeg_file, 0, SEEK_CUR);
                else
                    curpos = id3->filesize;

                if (num_tracks_in_memory() > 1)
                {
                    /* We have started loading other tracks that need to be
                       accounted for */
                    struct trackdata *track;
                    int i = 0;

                    while((track = get_trackdata(i++)))
                    {
                        curpos += track->id3.filesize;
                    }
                }

                diffpos = curpos - newpos;

                if(!filling && diffpos >= 0 && diffpos < audiobuflen)
                {
                    int unplayed_space_left, unswapped_space_left;

                    /* We are changing to a position that's already in
                       memory, so we just move the DMA read pointer. */
                    audiobuf_read = audiobuf_write - diffpos;
                    if (audiobuf_read < 0)
                    {
                        audiobuf_read += audiobuflen;
                    }

                    unplayed_space_left  = get_unplayed_space();
                    unswapped_space_left = get_unswapped_space();

                    /* If unswapped_space_left is larger than
                       unplayed_space_left, it means that the swapwrite pointer
                       hasn't yet advanced up to the new location of the read
                       pointer. We just move it, there is no need to swap
                       data that won't be played anyway. */

                    if (unswapped_space_left > unplayed_space_left)
                    {
                        DEBUGF("Moved swapwrite\n");
                        audiobuf_swapwrite = audiobuf_read;
                        play_pending = true;
                    }

                    if (mpeg_file>=0 && unplayed_space_left < low_watermark)
                    {
                        /* We need to load more data before starting */
                        filling = true;
                        queue_post(&mpeg_queue, MPEG_NEED_DATA, GENERATE_UNBUFFER_EVENTS);
                        play_pending = true;
                    }
                    else
                    {
                        /* resume will start at new position */
                        last_dma_chunk_size =
                            MIN(0x2000, get_unplayed_space_current_song());
                        mp3_play_data(mpeg_audiobuf + audiobuf_read,
                            last_dma_chunk_size, transfer_end);
                        dma_underrun = false;
                    }
                }
                else
                {
                    /* Move to the new position in the file and start
                       loading data */
                    reset_mp3_buffer();

                    if (num_tracks_in_memory() > 1)
                    {
                        /* We have to reload the current track */
                        close(mpeg_file);
                        remove_all_non_current_tags();
                        generate_unbuffer_events();
                        mpeg_file = -1;
                    }

                    if (mpeg_file < 0)
                    {
                        mpeg_file = open(id3->path, O_RDONLY);
                        if (mpeg_file < 0)
                        {
                            id3->elapsed = oldtime;
                            break;
                        }
                    }

                    if(-1 == lseek(mpeg_file, newpos, SEEK_SET))
                    {
                        id3->elapsed = oldtime;
                        break;
                    }

                    filling = true;
                    queue_post(&mpeg_queue, MPEG_NEED_DATA, 0);

                    /* Tell the file loading code that we want to start playing
                       as soon as we have some data */
                    play_pending = true;
                }

                id3->offset = newpos;

                break;
            }

            case MPEG_FLUSH_RELOAD: {
                int  numtracks    = num_tracks_in_memory();
                bool reload_track = false;

                if (numtracks > 1)
                {
                    /* Reset the buffer */
                    audiobuf_write = get_trackdata(1)->mempos;

                    /* Reset swapwrite unless we're still swapping current
                       track */
                    if (get_unplayed_space() <= get_playable_space())
                        audiobuf_swapwrite = audiobuf_write;

                    close(mpeg_file);
                    remove_all_non_current_tags();
                    generate_unbuffer_events();
                    mpeg_file = -1;
                    reload_track = true;
                }
                else if (numtracks == 1 && mpeg_file < 0)
                {
                    reload_track = true;
                }

                if(reload_track && new_file(1) >= 0)
                {
                    /* Tell ourselves that we want more data */
                    filling = true;
                    queue_post(&mpeg_queue, MPEG_NEED_DATA, 0);
                }

                break;
            }

            case MPEG_NEED_DATA:
                free_space_left = audiobuf_read - audiobuf_write;

                /* We interpret 0 as "empty buffer" */
                if(free_space_left <= 0)
                    free_space_left += audiobuflen;

                unplayed_space_left = audiobuflen - free_space_left;

                /* Make sure that we don't fill the entire buffer */
                free_space_left -= MPEG_HIGH_WATER;

                if (ev.data == GENERATE_UNBUFFER_EVENTS)
                    generate_unbuffer_events();

                /* do we have any more buffer space to fill? */
                if(free_space_left <= 0)
                {
                    DEBUGF("0\n");
                    filling = false;
                    generate_postbuffer_events();
                    storage_sleep();
                    break;
                }

                /* Read small chunks while we are below the low water mark */
                if(unplayed_space_left < low_watermark)
                    amount_to_read = MIN(MPEG_LOW_WATER_CHUNKSIZE,
                                         free_space_left);
                else
                    amount_to_read = free_space_left;

                /* Don't read more than until the end of the buffer */
                amount_to_read = MIN(audiobuflen - audiobuf_write,
                                     amount_to_read);
#if (CONFIG_STORAGE & STORAGE_MMC)
    /* MMC is slow, so don't read too large chunks */
                amount_to_read = MIN(0x40000, amount_to_read);
#elif MEMORYSIZE == 8
                amount_to_read = MIN(0x100000, amount_to_read);
#endif

                /* Read as much mpeg data as we can fit in the buffer */
                if(mpeg_file >= 0)
                {
                    DEBUGF("R\n");
                    t1 = current_tick;
                    len = read(mpeg_file, mpeg_audiobuf + audiobuf_write,
                               amount_to_read);
                    if(len > 0)
                    {
                        t2 = current_tick;
                        DEBUGF("time: %d\n", t2 - t1);
                        DEBUGF("R: %x\n", len);

                        /* Now make sure that we don't feed the MAS with ID3V1
                           data */
                        if (len < amount_to_read)
                        {
                            int i;
                            static const unsigned char tag[] = "TAG";
                            int taglen = 128;
                            int tagptr = audiobuf_write + len - 128;

                            /* Really rare case: entire potential tag wasn't
                               read in this call AND audiobuf_write < 128 */
                            if (tagptr < 0)
                                tagptr += audiobuflen;