Home » Archimedes archive » Archimedes World » AW-1996-02-Disc2.adf » !Z80Dem_Z80Demo » Docs/FileFormat/XZXformat
Docs/FileFormat/XZXformat
This website contains an archive of files for the Acorn Electron, BBC Micro, Acorn Archimedes, Commodore 16 and Commodore 64 computers, which Dominic Ford has rescued from his private collection of floppy disks and cassettes.
Some of these files were originally commercial releases in the 1980s and 1990s, but they are now widely available online. I assume that copyright over them is no longer being asserted. If you own the copyright and would like files to be removed, please contact me.
| Tape/disk: | Home » Archimedes archive » Archimedes World » AW-1996-02-Disc2.adf » !Z80Dem_Z80Demo |
| Filename: | Docs/FileFormat/XZXformat |
| Read OK: | ✔ |
| File size: | 08B2 bytes |
| Load address: | 0000 |
| Exec address: | 0000 |
File contents
Details of the level loading mechanism -------------------------------------- [for emulator authors, and any Speccy hackers interested in 'porting' multi-load games] The idea is that initially, a 48k snapshot - usually in .sna format - is loaded containing the game. Then, whenever the game would ordinarily load an extra section from tape, something like this happens; ... LD HL,address_to_load_data_at LD A,level_number DEFB 0EDh DEFB 0FBh ... This section will of course take the place of the original load-from-tape routine. The emulator then traps the opcode ED/FB, and loads a file at the specified address. Under xzx, the filenames are generated as follows (described as an sprintf() for clarity): sprintf(filename,"%s%d.dat",prefix,level_number); ...with the level_number being the value the A register had when the emulator trapped the opcode. In xzx, the prefix is taken from the 'basename' of the last snapshot loaded, e.g. "wibble.sna" -> "wibble". There is also provision for the re-loading of game-in-progress snapshots, such that you can directly supply the prefix used while specifying a snapshot to load, e.g. "game_name,my_game.sna". This will then read in game_name1.dat, game_name2.dat etc. as appropriate. If you're looking to 'port' a multi-load game, I find the best way to start is to load the main (first) part of the game, get a snapshot of that, and look for LD IX,nnnn. Many loaders use this, not just the ROM one used by the Basic. The next task is to find out where the level number is stored. If it isn't, or you can't find it, you'll need at least to find some way of finding out when a new game has started, so you can keep your own counter somewhere and zero it (or assign 1 to it, whatever) when a new game is started. Then you can put in the LD HL,nnnn, LD A,level etc. as mentioned above. If you've managed that much, in theory all that remains is to get the level data across. The ideal way to do that is to rip out the tape loader routine from your snapshot, and run that several times, saving to disk or whatever as you go along, then transferring kit + kaboodle later. This is only a very simplistic guide, but I hope it helps a little. - Russell Marks (rm1ajy2@gre.ac.uk)
00000000 44 65 74 61 69 6c 73 20 6f 66 20 74 68 65 20 6c |Details of the l| 00000010 65 76 65 6c 20 6c 6f 61 64 69 6e 67 20 6d 65 63 |evel loading mec| 00000020 68 61 6e 69 73 6d 0a 2d 2d 2d 2d 2d 2d 2d 2d 2d |hanism.---------| 00000030 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d |----------------| 00000040 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 2d 0a 5b 66 |-------------.[f| 00000050 6f 72 20 65 6d 75 6c 61 74 6f 72 20 61 75 74 68 |or emulator auth| 00000060 6f 72 73 2c 20 61 6e 64 20 61 6e 79 20 53 70 65 |ors, and any Spe| 00000070 63 63 79 20 68 61 63 6b 65 72 73 20 69 6e 74 65 |ccy hackers inte| 00000080 72 65 73 74 65 64 20 69 6e 20 27 70 6f 72 74 69 |rested in 'porti| 00000090 6e 67 27 0a 6d 75 6c 74 69 2d 6c 6f 61 64 20 67 |ng'.multi-load g| 000000a0 61 6d 65 73 5d 0a 0a 54 68 65 20 69 64 65 61 20 |ames]..The idea | 000000b0 69 73 20 74 68 61 74 20 69 6e 69 74 69 61 6c 6c |is that initiall| 000000c0 79 2c 20 61 20 34 38 6b 20 73 6e 61 70 73 68 6f |y, a 48k snapsho| 000000d0 74 20 2d 20 75 73 75 61 6c 6c 79 20 69 6e 20 2e |t - usually in .| 000000e0 73 6e 61 20 66 6f 72 6d 61 74 20 2d 20 69 73 0a |sna format - is.| 000000f0 6c 6f 61 64 65 64 20 63 6f 6e 74 61 69 6e 69 6e |loaded containin| 00000100 67 20 74 68 65 20 67 61 6d 65 2e 20 54 68 65 6e |g the game. Then| 00000110 2c 20 77 68 65 6e 65 76 65 72 20 74 68 65 20 67 |, whenever the g| 00000120 61 6d 65 20 77 6f 75 6c 64 20 6f 72 64 69 6e 61 |ame would ordina| 00000130 72 69 6c 79 20 6c 6f 61 64 20 61 6e 0a 65 78 74 |rily load an.ext| 00000140 72 61 20 73 65 63 74 69 6f 6e 20 66 72 6f 6d 20 |ra section from | 00000150 74 61 70 65 2c 20 73 6f 6d 65 74 68 69 6e 67 20 |tape, something | 00000160 6c 69 6b 65 20 74 68 69 73 20 68 61 70 70 65 6e |like this happen| 00000170 73 3b 0a 0a 2e 2e 2e 0a 4c 44 20 48 4c 2c 61 64 |s;......LD HL,ad| 00000180 64 72 65 73 73 5f 74 6f 5f 6c 6f 61 64 5f 64 61 |dress_to_load_da| 00000190 74 61 5f 61 74 0a 4c 44 20 41 2c 6c 65 76 65 6c |ta_at.LD A,level| 000001a0 5f 6e 75 6d 62 65 72 0a 44 45 46 42 20 30 45 44 |_number.DEFB 0ED| 000001b0 68 0a 44 45 46 42 20 30 46 42 68 0a 2e 2e 2e 0a |h.DEFB 0FBh.....| 000001c0 0a 54 68 69 73 20 73 65 63 74 69 6f 6e 20 77 69 |.This section wi| 000001d0 6c 6c 20 6f 66 20 63 6f 75 72 73 65 20 74 61 6b |ll of course tak| 000001e0 65 20 74 68 65 20 70 6c 61 63 65 20 6f 66 20 74 |e the place of t| 000001f0 68 65 20 6f 72 69 67 69 6e 61 6c 20 6c 6f 61 64 |he original load| 00000200 2d 66 72 6f 6d 2d 74 61 70 65 0a 72 6f 75 74 69 |-from-tape.routi| 00000210 6e 65 2e 20 54 68 65 20 65 6d 75 6c 61 74 6f 72 |ne. The emulator| 00000220 20 74 68 65 6e 20 74 72 61 70 73 20 74 68 65 20 | then traps the | 00000230 6f 70 63 6f 64 65 20 45 44 2f 46 42 2c 20 61 6e |opcode ED/FB, an| 00000240 64 20 6c 6f 61 64 73 20 61 20 66 69 6c 65 20 61 |d loads a file a| 00000250 74 20 74 68 65 0a 73 70 65 63 69 66 69 65 64 20 |t the.specified | 00000260 61 64 64 72 65 73 73 2e 20 55 6e 64 65 72 20 78 |address. Under x| 00000270 7a 78 2c 20 74 68 65 20 66 69 6c 65 6e 61 6d 65 |zx, the filename| 00000280 73 20 61 72 65 20 67 65 6e 65 72 61 74 65 64 20 |s are generated | 00000290 61 73 20 66 6f 6c 6c 6f 77 73 0a 28 64 65 73 63 |as follows.(desc| 000002a0 72 69 62 65 64 20 61 73 20 61 6e 20 73 70 72 69 |ribed as an spri| 000002b0 6e 74 66 28 29 20 66 6f 72 20 63 6c 61 72 69 74 |ntf() for clarit| 000002c0 79 29 3a 0a 0a 09 73 70 72 69 6e 74 66 28 66 69 |y):...sprintf(fi| 000002d0 6c 65 6e 61 6d 65 2c 22 25 73 25 64 2e 64 61 74 |lename,"%s%d.dat| 000002e0 22 2c 70 72 65 66 69 78 2c 6c 65 76 65 6c 5f 6e |",prefix,level_n| 000002f0 75 6d 62 65 72 29 3b 0a 0a 2e 2e 2e 77 69 74 68 |umber);.....with| 00000300 20 74 68 65 20 6c 65 76 65 6c 5f 6e 75 6d 62 65 | the level_numbe| 00000310 72 20 62 65 69 6e 67 20 74 68 65 20 76 61 6c 75 |r being the valu| 00000320 65 20 74 68 65 20 41 20 72 65 67 69 73 74 65 72 |e the A register| 00000330 20 68 61 64 20 77 68 65 6e 20 74 68 65 0a 65 6d | had when the.em| 00000340 75 6c 61 74 6f 72 20 74 72 61 70 70 65 64 20 74 |ulator trapped t| 00000350 68 65 20 6f 70 63 6f 64 65 2e 0a 0a 49 6e 20 78 |he opcode...In x| 00000360 7a 78 2c 20 74 68 65 20 70 72 65 66 69 78 20 69 |zx, the prefix i| 00000370 73 20 74 61 6b 65 6e 20 66 72 6f 6d 20 74 68 65 |s taken from the| 00000380 20 27 62 61 73 65 6e 61 6d 65 27 20 6f 66 20 74 | 'basename' of t| 00000390 68 65 20 6c 61 73 74 20 73 6e 61 70 73 68 6f 74 |he last snapshot| 000003a0 20 6c 6f 61 64 65 64 2c 0a 65 2e 67 2e 20 22 77 | loaded,.e.g. "w| 000003b0 69 62 62 6c 65 2e 73 6e 61 22 20 2d 3e 20 22 77 |ibble.sna" -> "w| 000003c0 69 62 62 6c 65 22 2e 20 54 68 65 72 65 20 69 73 |ibble". There is| 000003d0 20 61 6c 73 6f 20 70 72 6f 76 69 73 69 6f 6e 20 | also provision | 000003e0 66 6f 72 20 74 68 65 20 72 65 2d 6c 6f 61 64 69 |for the re-loadi| 000003f0 6e 67 20 6f 66 0a 67 61 6d 65 2d 69 6e 2d 70 72 |ng of.game-in-pr| 00000400 6f 67 72 65 73 73 20 73 6e 61 70 73 68 6f 74 73 |ogress snapshots| 00000410 2c 20 73 75 63 68 20 74 68 61 74 20 79 6f 75 20 |, such that you | 00000420 63 61 6e 20 64 69 72 65 63 74 6c 79 20 73 75 70 |can directly sup| 00000430 70 6c 79 20 74 68 65 20 70 72 65 66 69 78 0a 75 |ply the prefix.u| 00000440 73 65 64 20 77 68 69 6c 65 20 73 70 65 63 69 66 |sed while specif| 00000450 79 69 6e 67 20 61 20 73 6e 61 70 73 68 6f 74 20 |ying a snapshot | 00000460 74 6f 20 6c 6f 61 64 2c 20 65 2e 67 2e 20 22 67 |to load, e.g. "g| 00000470 61 6d 65 5f 6e 61 6d 65 2c 6d 79 5f 67 61 6d 65 |ame_name,my_game| 00000480 2e 73 6e 61 22 2e 20 54 68 69 73 0a 77 69 6c 6c |.sna". This.will| 00000490 20 74 68 65 6e 20 72 65 61 64 20 69 6e 20 67 61 | then read in ga| 000004a0 6d 65 5f 6e 61 6d 65 31 2e 64 61 74 2c 20 67 61 |me_name1.dat, ga| 000004b0 6d 65 5f 6e 61 6d 65 32 2e 64 61 74 20 65 74 63 |me_name2.dat etc| 000004c0 2e 20 61 73 20 61 70 70 72 6f 70 72 69 61 74 65 |. as appropriate| 000004d0 2e 0a 0a 49 66 20 79 6f 75 27 72 65 20 6c 6f 6f |...If you're loo| 000004e0 6b 69 6e 67 20 74 6f 20 27 70 6f 72 74 27 20 61 |king to 'port' a| 000004f0 20 6d 75 6c 74 69 2d 6c 6f 61 64 20 67 61 6d 65 | multi-load game| 00000500 2c 20 49 20 66 69 6e 64 20 74 68 65 20 62 65 73 |, I find the bes| 00000510 74 20 77 61 79 20 74 6f 20 73 74 61 72 74 0a 69 |t way to start.i| 00000520 73 20 74 6f 20 6c 6f 61 64 20 74 68 65 20 6d 61 |s to load the ma| 00000530 69 6e 20 28 66 69 72 73 74 29 20 70 61 72 74 20 |in (first) part | 00000540 6f 66 20 74 68 65 20 67 61 6d 65 2c 20 67 65 74 |of the game, get| 00000550 20 61 20 73 6e 61 70 73 68 6f 74 20 6f 66 20 74 | a snapshot of t| 00000560 68 61 74 2c 20 61 6e 64 0a 6c 6f 6f 6b 20 66 6f |hat, and.look fo| 00000570 72 20 4c 44 20 49 58 2c 6e 6e 6e 6e 2e 20 4d 61 |r LD IX,nnnn. Ma| 00000580 6e 79 20 6c 6f 61 64 65 72 73 20 75 73 65 20 74 |ny loaders use t| 00000590 68 69 73 2c 20 6e 6f 74 20 6a 75 73 74 20 74 68 |his, not just th| 000005a0 65 20 52 4f 4d 20 6f 6e 65 20 75 73 65 64 20 62 |e ROM one used b| 000005b0 79 20 74 68 65 0a 42 61 73 69 63 2e 0a 0a 54 68 |y the.Basic...Th| 000005c0 65 20 6e 65 78 74 20 74 61 73 6b 20 69 73 20 74 |e next task is t| 000005d0 6f 20 66 69 6e 64 20 6f 75 74 20 77 68 65 72 65 |o find out where| 000005e0 20 74 68 65 20 6c 65 76 65 6c 20 6e 75 6d 62 65 | the level numbe| 000005f0 72 20 69 73 20 73 74 6f 72 65 64 2e 20 49 66 20 |r is stored. If | 00000600 69 74 20 69 73 6e 27 74 2c 0a 6f 72 20 79 6f 75 |it isn't,.or you| 00000610 20 63 61 6e 27 74 20 66 69 6e 64 20 69 74 2c 20 | can't find it, | 00000620 79 6f 75 27 6c 6c 20 6e 65 65 64 20 61 74 20 6c |you'll need at l| 00000630 65 61 73 74 20 74 6f 20 66 69 6e 64 20 73 6f 6d |east to find som| 00000640 65 20 77 61 79 20 6f 66 20 66 69 6e 64 69 6e 67 |e way of finding| 00000650 20 6f 75 74 0a 77 68 65 6e 20 61 20 6e 65 77 20 | out.when a new | 00000660 67 61 6d 65 20 68 61 73 20 73 74 61 72 74 65 64 |game has started| 00000670 2c 20 73 6f 20 79 6f 75 20 63 61 6e 20 6b 65 65 |, so you can kee| 00000680 70 20 79 6f 75 72 20 6f 77 6e 20 63 6f 75 6e 74 |p your own count| 00000690 65 72 20 73 6f 6d 65 77 68 65 72 65 20 61 6e 64 |er somewhere and| 000006a0 0a 7a 65 72 6f 20 69 74 20 28 6f 72 20 61 73 73 |.zero it (or ass| 000006b0 69 67 6e 20 31 20 74 6f 20 69 74 2c 20 77 68 61 |ign 1 to it, wha| 000006c0 74 65 76 65 72 29 20 77 68 65 6e 20 61 20 6e 65 |tever) when a ne| 000006d0 77 20 67 61 6d 65 20 69 73 20 73 74 61 72 74 65 |w game is starte| 000006e0 64 2e 20 54 68 65 6e 20 79 6f 75 0a 63 61 6e 20 |d. Then you.can | 000006f0 70 75 74 20 69 6e 20 74 68 65 20 4c 44 20 48 4c |put in the LD HL| 00000700 2c 6e 6e 6e 6e 2c 20 4c 44 20 41 2c 6c 65 76 65 |,nnnn, LD A,leve| 00000710 6c 20 65 74 63 2e 20 61 73 20 6d 65 6e 74 69 6f |l etc. as mentio| 00000720 6e 65 64 20 61 62 6f 76 65 2e 0a 0a 49 66 20 79 |ned above...If y| 00000730 6f 75 27 76 65 20 6d 61 6e 61 67 65 64 20 74 68 |ou've managed th| 00000740 61 74 20 6d 75 63 68 2c 20 69 6e 20 74 68 65 6f |at much, in theo| 00000750 72 79 20 61 6c 6c 20 74 68 61 74 20 72 65 6d 61 |ry all that rema| 00000760 69 6e 73 20 69 73 20 74 6f 20 67 65 74 20 74 68 |ins is to get th| 00000770 65 20 6c 65 76 65 6c 0a 64 61 74 61 20 61 63 72 |e level.data acr| 00000780 6f 73 73 2e 20 54 68 65 20 69 64 65 61 6c 20 77 |oss. The ideal w| 00000790 61 79 20 74 6f 20 64 6f 20 74 68 61 74 20 69 73 |ay to do that is| 000007a0 20 74 6f 20 72 69 70 20 6f 75 74 20 74 68 65 20 | to rip out the | 000007b0 74 61 70 65 20 6c 6f 61 64 65 72 20 72 6f 75 74 |tape loader rout| 000007c0 69 6e 65 0a 66 72 6f 6d 20 79 6f 75 72 20 73 6e |ine.from your sn| 000007d0 61 70 73 68 6f 74 2c 20 61 6e 64 20 72 75 6e 20 |apshot, and run | 000007e0 74 68 61 74 20 73 65 76 65 72 61 6c 20 74 69 6d |that several tim| 000007f0 65 73 2c 20 73 61 76 69 6e 67 20 74 6f 20 64 69 |es, saving to di| 00000800 73 6b 20 6f 72 20 77 68 61 74 65 76 65 72 0a 61 |sk or whatever.a| 00000810 73 20 79 6f 75 20 67 6f 20 61 6c 6f 6e 67 2c 20 |s you go along, | 00000820 74 68 65 6e 20 74 72 61 6e 73 66 65 72 72 69 6e |then transferrin| 00000830 67 20 6b 69 74 20 2b 20 6b 61 62 6f 6f 64 6c 65 |g kit + kaboodle| 00000840 20 6c 61 74 65 72 2e 0a 0a 54 68 69 73 20 69 73 | later...This is| 00000850 20 6f 6e 6c 79 20 61 20 76 65 72 79 20 73 69 6d | only a very sim| 00000860 70 6c 69 73 74 69 63 20 67 75 69 64 65 2c 20 62 |plistic guide, b| 00000870 75 74 20 49 20 68 6f 70 65 20 69 74 20 68 65 6c |ut I hope it hel| 00000880 70 73 20 61 20 6c 69 74 74 6c 65 2e 0a 0a 2d 20 |ps a little...- | 00000890 52 75 73 73 65 6c 6c 20 4d 61 72 6b 73 20 28 72 |Russell Marks (r| 000008a0 6d 31 61 6a 79 32 40 67 72 65 2e 61 63 2e 75 6b |m1ajy2@gre.ac.uk| 000008b0 29 0a |).| 000008b2
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