id3.c

这项工程将让您把自己的MP3播放器平台

//++
//id3.c - MP3 Player Compact Flash Card functions
//
// Copyright (C) 2005 by Spare Time Gizmos.  All rights reserved.
//
// This file is part of the Spare Time Gizmos' MP3 Player firmware.
//
// This firmware 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.
//
//DESCRIPTION:
//
//REFERENCES:
//	http://en.wikipedia.org/wiki/ID3
//
//REVISION HISTORY:
// dd-mmm-yy    who     description
// 19-Oct-05	RLA	Split off from fat.c
// 			Add STACKSLOCS hack to ReadID3Tag() for SDCC.
//--

// Include files...
#include <stdio.h>		// needed so DBGOUT(()) can find printf!
#include <string.h>		// strcpy(), etc...
#include "standard.h"		// standard types - BYTE, WORD, BOOL, etc
#include "buffer.h"		// Buffer management functions
#include "fat.h"		// declarations for this module
#include "id3.h"		// ID3 v1.1 definitions


// Public members...
PUBLIC XDATA char g_szArtistName[ID3_MAX_ARTIST_NAME];
PUBLIC XDATA char g_szTrackName[ID3_MAX_TRACK_NAME];


//++
//   This routine will read the last 128 bytes of the specified file and then
// does some rudimentary checking of the ID3 tag signature to ensure that it's
// valid.  If the file does contain a valid ID3 tag, then the artist and track
// names are stored in the XDATA globals g_szArtistName/g_szTrackName and TRUE
// is returned.
//
//   Ideally we'd just like to return the entire ID3_TAG structure as a global,
// but that contains a lot of fields that we never use and takes up 128 bytes
// of XDATA RAM.  The artist and track names alone, however, only take 60 bytes.
// It's not a problem on the P89C668, but with the '664 MCU XDATA is tight! 
//
//   Note that this requires a temporary buffer in which store the ID3 tag while
// we extract the artist and track names.  One is easily allocated from the disk
// buffer pool, however we must be sure to release it before we return!
//--
PUBLIC BOOL ReadID3Tag (PXDIRENT pxDirEnt) STACKSLOCS
{
  PIBCB pBCB;  PXID3TAG pxTag; 
  memset(&g_szArtistName, 0, ID3_MAX_ARTIST_NAME);
  memset(&g_szTrackName, 0, ID3_MAX_TRACK_NAME);

  // Allocate a buffer and open the file...
  ALLOCATE_BUFFER(pBCB);
  if (pBCB == NULL) return FALSE;
  pxTag = (ID3_TAG XDATA *) pBCB->pbBuffer;
  OpenFile(pxDirEnt);

  //   Attempt to read the tag.  If we fail (which can only happen in the case
  // of a hardware error!) then just give up...
  if (!ReadFileEnd((PXBYTE) pxTag, ID3_TAG_SIZE)) goto NOTAG;

  //   Ok, we've got _something_.  Now do a few simple checks to see if it's
  // really an ID3 tag or not.
  if (   (pxTag->abID3[0] != 'T')
      || (pxTag->abID3[1] != 'A')
      || (pxTag->abID3[2] != 'G')) goto NOTAG;
  if ((strlen(pxTag->szArtistName) == 0) && (strlen(pxTag->szTrackName) == 0)) goto NOTAG;
  DBGOUT(("ReadID3Tag: artist=\"%.30s\", title=\"%.30s\"\n", pxTag->szArtistName, pxTag->szTrackName));

  // Looks like a good tag - extract the artist and track names, and return TRUE.
  strcpy(g_szArtistName, pxTag->szArtistName);
  strcpy(g_szTrackName, pxTag->szTrackName);
  CloseFile();  RELEASE_BUFFER(pBCB);  return TRUE;

  // Here if there is no tag.  Close the file, release the buffer, and return FALSE.
NOTAG:
  CloseFile();  RELEASE_BUFFER(pBCB);  return FALSE;
}