Some Atomiswave info

 
 Some notes about Atomiswave carts data reading

 Even if Atomisvawe itself is mostly the same as Naomi, cartridge subsystem is
 different from Naomi/Naomi2 rom-board system.

 First of all, there is no (or rather totally unused) PIO data reading. All
 data comes throught DMA only.

 Another one, there is two independent data areas, for main programm code and
 for all other game data. First area contains in EPR-ROM chip (8Mb), second
 one contains in MPR-ROM chips (up to 128Mb). Each one area uses it's own
 offset registers and all offsets are relative from start of this area.

 Last one, game data area itself consists from two sub-areas: linear file system
 (array of 64-byte records with file names, file offsets and other information)
 and file data sub-area. Even there is one physical MPR-ROM data area, there
 is two different offset registers to access each sub-areaseparately. Each register
 is specific to it's own sub-area.
 
 All these offsets registers manage only one main internal offset register to
 work with one generic DMA. Each register access changes internal DMA offset
 according to it's behavior.

 All offsets used in these registers (except special indexes), are indexes of first
 word of requested data. Actual offset in bytes just shifted right to one bit.
 
 AW_EPR_OFFSETL                                          Register addres: 0x5f7000
 +-------------------------------------------------------------------------------+
 |                                  bit15-0                                      |
 +-------------------------------------------------------------------------------+
 |                         EPR data offset low word                              |
 +-------------------------------------------------------------------------------+

 AW_EPR_OFFSETH                                          Register addres: 0x5f7004
 +-------------------------------------------------------------------------------+
 |                                  bit15-0                                      |
 +-------------------------------------------------------------------------------+
 |                          EPR data offset hi word                              |
 +-------------------------------------------------------------------------------+

  Both low and high words of 32-bit offset from start of EPR-ROM area. Used for
  reading header and programm code data, cannot be used for reading MPR-ROMs data.
  
 AW_MPR_RECORD_INDEX                                     Register addres: 0x5f700c
 +-------------------------------------------------------------------------------+
 |                                  bit15-0                                      |
 +-------------------------------------------------------------------------------+
 |                          File system record index                             |
 +-------------------------------------------------------------------------------+
  
  This register contains index of MPR-ROM file system record (64-bytes in size) to
  read throught DMA. Internal DMA offset register is assigned as AW_MPR_RECORD_INDEX<<6
  from start of MPR-ROM area. Size of DMA transaction not limited, it is possible
  to read any number of records or just part of it.
  
 AW_MPR_FIRST_FILE_INDEX                                 Register addres: 0x5f7010
 +-------------------------------------------------------------------------------+
 |                                  bit15-0                                      |
 +-------------------------------------------------------------------------------+
 |                           First file record index                             |
 +-------------------------------------------------------------------------------+
  
  This register assign for internal cart circuit index of record in MPR-ROM file
  system sub-area that contain information about first file of MPR-ROM files
  sub-area. Internal circuit using this record to read absolute first file offset
  from start of MPR-ROM area and calculate normal offset for each other file
  requested, since MPR-ROM file data sub-area can be assighed only with relative
  offsets from start of such sub-area.
  
 AW_MPR_FILE_OFFSETL                                     Register addres: 0x5f7014
 +-------------------------------------------------------------------------------+
 |                                  bit15-0                                      |
 +-------------------------------------------------------------------------------+
 |                         MPR file offset low word                              |
 +-------------------------------------------------------------------------------+

 AW_MPR_FILE_OFFSETH                                     Register addres: 0x5f7018
 +-------------------------------------------------------------------------------+
 |                                  bit15-0                                      |
 +-------------------------------------------------------------------------------+
 |                          MPR file offset hi word                              |
 +-------------------------------------------------------------------------------+
  
  Both low and high words of 32-bit relative offset from start of MPR-ROM files
  sub-area. Used by internal circuit to calculate absolute offset using data
  from AW_MPR_FIRST_FILE_INDEX register. Cannot be used for reading EPR-ROM
  data nor even MPR-ROM file system sub-area data.

 
 In short:
 

     EPR-ROM 
 +--------------+ 0x00000000
 |              |
 |    HEADER    +- AW_EPR_OFFSET << 1
 |              |
 +--------------+
 |              |
 |     CODE     +- AW_EPR_OFFSET << 1
 |              |
 |              |
 +--------------+ 0x007fffff
 
     MPR-ROMS
 +--------------+ 0x00000000
 | FS_HEADER    |
 | FS_RECORD[1] +- (AW_MPR_RECORD_INDEX << 6)
 | FS_RECORD[2] |
 | FS_RECORD[3] +- (AW_MPR_FIRST_FILE_INDEX << 6)
 |     ...      |
 | FS_RECORD[N] |
 +--------------+- FS_RECORD[AW_MPR_FIRST_FILE_INDEX].FILE_ABS_OFFSET
 | FILE_0       | 
 | FILE_1       +- (AW_MPR_FILE_OFFSET << 1) + FS_RECORD[AW_MPR_FIRST_FILE_INDEX].FILE_ABS_OFFSET
 |     ...      |
 | FILE_N       |
 +--------------+ 0x07ffffff
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