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Reserved disk space features.
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This new release implements reserved disk space feature.
Reserved disk space allows to download/update data (like font, setup, ...)
inside on-board memory.

Reserved disk space can be read/write :
	- by low-level function from on-board application, at any time
	- by operating system (Windows) only when player is set in 
	  a specific mode (update mode). In this mode, all disk space
          can be scan.

If player is not in update mode, operating system will not be able to read/write
this reserved disk space (and so modify or erase it), even during a format command.

To download/update data in reserved disk space, player have to be set in update mode.
In this mode :
  - From mass storage, all memory can be accessed.
  - FAT have a specific initialization. (all clusters are used except reserved disk space cluster)

Then, you just have to download a file that contain data. (by using USB / drag & drop)

Use :
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1) Defines the reserved space size in config.h file :

    Example :
    if requested reserved space is 512Kbytes, place in config.h

    #define MEM_RESERVED_SIZE     1024           /* Reserved disk space in sector */
    Size sector is 512bytes.

2) Switch player in update mode. For this, set reserved_disk_space bit variable to TRUE, 
   and call format memory on-board function.
   This operation will make a specific initialization for FAT, that will allows to download
   data in the reserved disk space.
   reserved_disk_space bit is declared in variables.c file.

3) Then, plug the board to PC (using USB) and download file(s) that contain datas.

4) Set reserved_disk_space bit to FALSE, and launch format on-board memory.
   Format is mandatory and will not erase data.


Notes:
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CHS definition.
  format (fat_format(void)) needs to know the value of number of cylinder, head and sector.
  Number of cylinder is different in normal mode / update mode.

  Example :
  If total memory CHS parameters are :
    Cylinder number : 500
    Head            :  16
    Sector          :  32
  and if reserved disk size is 1024 sectors (512Kbytes), in normal mode, the CHS parameters will be
    Cylinder number : 500 - (1024 / (16 * 32)) = 498
    Head            :  16
    Sector          :  32

MEM_RESERVED_SIZE must be a multiple by 2 of (Nb_head x Nb_sector) 
(refer to CHS definition)

Starting address of specific data can be calculated as follow :

xxx_reserved_space_start = xxx_mem_size + 1;

with 

xxx_mem_size = total number of sector of memory minus the reserved disk space.


Reserved area is not erased after a call to format function (on-board), in both mode 
(normal or update).