SEGA Master System format

From Princed Wiki
Revision as of 14:58, 20 October 2019 by Norbert (talk | contribs) (Objects' data: typo)
Jump to: navigation, search

This document describes the format of data in Prince of Persia 1 for the Sega Master System.

(A similar but slightly different version was released for the Sega Game Gear.)

General

Byte order

Little-endian (Intel) byte order is used, unless noted otherwise. This is the native endianness of the Z80 CPU in the Sega Master System.

Addresses

There are two kinds of addresses (pointers) in the ROM. Both are stored on 2 bytes.

1. Linear addresses. These are simply an address into the ROM. Linear pointers can address only the first 64 kiB of the ROM, but they can point to any byte within that area.

2. Banked addresses. These can be converted to linear addresses with the following code:

int BankedToLinear(int address) {
	int bank = address & 0x000F;
	int offset = address & 0xFFF0;
	// assert(0x8000 <= offset && offset <= 0xBFFF);
	return (bank << 14) + (offset - 0x8000);
}

Banked pointers can address the whole 256 kiB of the ROM, but only in increments of 16 bytes.

Levels

The level table

The level table starts at offset 0x6A7C. (TODO: In the Game Gear version it starts at 0x719C.)

There are 14 levels. The table stores 20 bytes about each level:

Size Contents
2 bytes Always 0x60C9.
2 bytes Banked address of graphics tiles: 0x8003 (0x0C000) for dungeon levels, 0x94C3 (0x0D4C0) for palace levels.
2 bytes Linear address of level tiles (2x2 blocks of graphics tiles): 0xA5B2 for dungeon levels, 0xA8D2 for palace levels.
2 bytes Banked address of level's #Graphics map.
1 byte Level type: 0x05=dungeon, 0x85=palace.
1 byte Starting direction: 0x00=left, 0x20=right.
1 byte Starting X coordinate.
1 byte Starting Y coordinate.
1 byte Starting room. (0..23)
1 byte Starting animation.
4 bytes Unknown. Their values are frequently similar to the previous 4 bytes.
2 bytes Linear address of the level's #Room links and objects table.

Graphics map

The first 64 bytes contain the list of level tiles used in the map. Unused entries are filled with 0xFF.

After that comes the map itself. Each level is 128 tiles wide and 36 tiles tall. (Levels 13 and 14 are shorter, they are only 24 and 12 tiles tall, respectively.)

Each tile index is stored on 6 bits, so the level is 128*6/8 = 96 bytes wide.

The bits are read starting from the least significant bit of each byte.

The map consists of 24 rooms arranged in 3 rows and 8 columns. (Level 13 and 14 contain only 2 and 1 rows of rooms, respectively.) Each room is 36/3=12 tiles tall and 128/8=16 tiles wide.

(TODO: Which tiles are walls or floors?)

Room links and objects table

This table is preceded by a 2-byte number which tells the length of the following chunk of data. All offsets stored within this table are interpreted as offsets within this chunk.

The data within the chunk is arranged as follows:

Size Contents
24*2 bytes The offset of the #Objects' data for each room. Zero if the room doesn't exist.
24*4 bytes Room links for each room.

Unlike in most other versions of PoP, their order is above,right,below,left.
The rooms are numbered from 0 to 23 (0x00 to 0x17). 0xFF means no room. 0x80 means a special exit (used on level 6 and 12).

the rest #Objects' data.

Level 14 is special: Only the first 8 rooms exist. The rest of the rooms have zero offsets. The room links are included only for the first 5 rooms.

You can detect the number of rooms from the first offset: (offset-0x30)/4 gives how many rooms have room links.

Objects' data

Each object is stored as a byte telling what kind of object it is, followed by argument bytes whose number and meaning depends on the type of the object.

(TODO: figure out the unknown argument bytes)

value object argument bytes notes
0x27 level door xx yy tt 07 00 uu 00 x*=8,y*=8; If fourth byte is not 07 then the door opens by itself.

tt is 01 or 02, uu is 00 or FA

0x29 mirror (level 4) xx yy tt rx ry tt: DE, rx/ry are the reflection
0x2B spike xx yy
0x2C sword xx yy
0x2D red (hurt) potion xx yy
0x2E blue (heal) potion xx yy
0x2F green (life) potion xx yy
0x30 pink (slow fall) potion xx yy
0x31 chomper xx yy
0x32 gate xx yy cl tt op uu 00 cl: 02 or FF, tt: 01 or 07, op: 0-5 (05 or 1F), uu: 8C,FA,FE
0x3E skeleton wake up (level 3) 07 01 40 xx yy x*=32,y*=64;
0x3F skeleton continue (level 3) 08 01 40 xx yy x*=32,y*=64;
0x40 skeleton (level 3) xx yy Used after the other two skeleton objects, but why?
0x41 loose floor xx yy x*=8,y*=8;
0x42 falling loose floor (level 13) xx yy x*=8,y*=8;
0x61 close button xx yy ww ln ln x*=8,y*=8; ln: address of triggered object within the level data chunk.

For some reason, exit doors are always triggered by close buttons.
ww: 00 (without wall), 02 (with wall)

0x62 open button xx yy ww ln ln x*=8,y*=8; ln: address of triggered object within the level data chunk.

ww: 00 (without wall), 02 (with wall)

0x64 enemy cd tp an xx yy cd: color and direction (00-25), tp: type (00=guard,01=skel,02=Jaffar), an:animation (B5)
0x66 shadow steps (level 6) xx yy
0x69 shadow steals (level 5) xx yy
0x6F princess (level 14) xx yy object is added later?
0x70 mouse (level 8) xx yy
0x74 shadow fights (level 12) xx yy
0xFF end - Marks the end of object data for this room.

TODO

  • Tiles
  • Sprites
  • Texts
  • (Music???)