az_network Posted January 31, 2011 Share Posted January 31, 2011 Hi, here enclosed you find the commented source code of Demon Attack for Atari 2600. I enclose also a version of the same game with infinite lives. Regards, A. demonatk.zip demon_hacked.bin 1 Quote Link to comment Share on other sites More sharing options...
Nukey Shay Posted January 31, 2011 Share Posted January 31, 2011 Hi, here enclosed you find the commented source code of Demon Attackfor Atari 2600. Close...but there are still vectors you missed. Such as L12EF, which holds destination addresses that are pushed onto the stack and then RTS'ed to (because RTS is handling them, the addresses are all -1 from the actual address). ex: L12EF: .word LF1388-1 .word LF135C-1 .word LF134F-1 .word LF12F7-1 1 Quote Link to comment Share on other sites More sharing options...
az_network Posted January 31, 2011 Author Share Posted January 31, 2011 Hi, here enclosed you find the commented source code of Demon Attackfor Atari 2600. Close...but there are still vectors you missed. Such as L12EF, which holds destination addresses that are pushed onto the stack and then RTS'ed to (because RTS is handling them, the addresses are all -1 from the actual address). ex: L12EF: .word LF1388-1 .word LF135C-1 .word LF134F-1 .word LF12F7-1 Hi, thank you for your reply. Indeed, few lines before you see an explanation of the addresses in table L12EF, and the commented lines of subroutines (SUB1), (SUB2), etc. take in due account the actual +1 address (i.e. SUB 7 starting line is at $12F7, but stack address is $12F6). Do you suggest to use ".word LF12F7-1" in table to express more clearly the actual starting addresses of subroutins ? LDA SoundIndex ;3 if SoundIndex = 0 0 0 0 x x x x ---> save $1387 on stack (SUB4) AND #$F0 ;2 LSR ;2 if SoundIndex = 0 0 0 1 x x x x ---> save $135B on stack (SUB5) LSR ;2 LSR ;2 if SoundIndex = 0 0 1 0 x x x x ---> save $134E on stack (SUB6) TAY ;2 LDA L12F0,Y ;4 if SoundIndex = 0 1 0 0 x x x x ---> save $12F6 on stack (SUB7) Anyway, I learned a nice way to embed a "ON x GOSUB" instruction in assembler !!! regards, A. Quote Link to comment Share on other sites More sharing options...
az_network Posted January 31, 2011 Author Share Posted January 31, 2011 Somebody created a translation of the original Demon Attack in java (from the website Meatfighter). The enclosed file could be useful to better understand the dynamics of game. There is still a lot of work to do... A. demon_java.zip Quote Link to comment Share on other sites More sharing options...
Nukey Shay Posted January 31, 2011 Share Posted January 31, 2011 Do you suggest to use ".word LF12F7-1" in table to express more clearly the actual starting addresses of subroutins ? Yes, because that is the easiest way to keep the table values correct should a user add or delete code...just have the assembler do it for you. Otherwise, it's just a collection of values that may or may not be correct (and inadvertantly cause the program to glitch or crash). Describing what something is used for is the basic purpose of any source code...whether it's a value, labelled destination, subroutine, etc. As more of the code is reverse-engineered and understood...something like this: LDA L12F0,Y ;4 PHA ;3 LDA L12EF,Y ;4 PHA ;3 RTS ;6 L12EF: .byte $87 ; |X XXX| $12EF L12F0: .byte $13 ; | X XX| $12F0 .byte $5B ; | X XX XX| $12F1 .byte $13 ; | X XX| $12F2 .byte $4E ; | X XXX | $12F3 .byte $13 ; | X XX| $12F4 .byte $F6 ; |XXXX XX | $12F5 .byte $12 ; | X X | $12F6 ...becomes this: LDA L12EF+1,Y ;4 MSB PHA ;3 LDA L12EF,Y ;4 LSB PHA ;3 RTS ;6 Do sound effect for v1 L12EF: ; SoundIndex bits 5-4 / effect .word L1388-1 ; 0 0 / no sound .word L135C-1 ; 0 1 / regular background noise .word L134F-1 ; 1 0 / demon exploding .word L12F7-1 ; 1 1 / end-of-game The labels themselves can be search/replaced to describe what they are used for. In that case, the table would read something like this: ;jump table for voice1 sound effects... v1_sound_tbl: ; SoundIndex bits 5-4 .word v1_no_sound-1 ; 0 0 .word v1_reg_background-1 ; 0 1 .word v1_demon_explode-1 ; 1 0 .word v1_end_of_game-1 ; 1 1 Much more easy to read than just a collection of generic labels that Distella assigned Quote Link to comment Share on other sites More sharing options...
az_network Posted January 31, 2011 Author Share Posted January 31, 2011 Thank you for the very clear explanation !!! A. Quote Link to comment Share on other sites More sharing options...
ComputerSpaceFan Posted February 1, 2011 Share Posted February 1, 2011 Can I ask, on behalf of those of us who don't speak the assembler language you are parlaying, does the "commented source code" version mean this is the original ROM that ends at Level 256? (Sorry for my ignorance, I am trying desperately to get the original game-ends-at-256 version anywhere I can) Quote Link to comment Share on other sites More sharing options...
Nukey Shay Posted February 1, 2011 Share Posted February 1, 2011 (edited) The original ROM crashes after level 84...not 255. The code specifically checks for that level, and enters an infinite loop (it's not a bug). ; @ = $147C .SinglePlayer: INC LEVEL ;5 LEVEL = LEVEL +1 .ContinueOnTheSameLevel: LDA LEVEL ;3 CMP #$54 ;2 LEVEL = 84 ? .NeverEndingLoop: IF NTSC BEQ .NeverEndingLoop ; after 84 levels game crashes (if NTSC) ELSE NOP NOP ENDIF "IF NTSC" above should read "IF ORIGINAL", actually Both versions exist for PAL and NTSC. The game-crashing loop appears in the binaries that include "(Imagic w-Picture Label)" as part of the filenames in ROM's set. Originals.zip Edited February 1, 2011 by Nukey Shay Quote Link to comment Share on other sites More sharing options...
Nukey Shay Posted February 1, 2011 Share Posted February 1, 2011 I should mention that the description "w-picture label" used in the filenames is also misleading. Rob altered the game when the picture label cart variation was in production...so all of the text label carts (I think) should feature the infinite loop, but it's still present in some of the picture label carts. Look here: http://www.atariage.com/forums/topic/161476-how-long-to-test-if-demon-attack-is-the-one-that-crashes/ Quote Link to comment Share on other sites More sharing options...
az_network Posted February 1, 2011 Author Share Posted February 1, 2011 I started to do some experiments. The original Demon Attack is a 4K cartridge. It is possible to use the bank switch in order to double the number of demons waves in a 8k Demon Attack. At some point of the game I just switch to a different bank where different graphics is available. Just by chance this happens when the player wins an extra life, because the sound music access to the final addresses of the 4k, and eventually access to the switch registers. Furthermore, using the option of multiple players (NUSIZE0-1) it is possible to multiply the number of moving demons on screen. Here attached you see an example (Scorpion is my chosen brand for the games). Please, consider that is just an experiment to extend existing games, not a real game. A. demon8k.zip Quote Link to comment Share on other sites More sharing options...
ComputerSpaceFan Posted February 2, 2011 Share Posted February 2, 2011 I should mention that the description "w-picture label" used in the filenames is also misleading. Rob altered the game when the picture label cart variation was in production...so all of the text label carts (I think) should feature the infinite loop, but it's still present in some of the picture label carts. Look here: http://www.atariage.com/forums/topic/161476-how-long-to-test-if-demon-attack-is-the-one-that-crashes/ Ooops I forgot it was actually 84 levels, not 255 AND I forgot I asked this before in that other thread! Oh well, it's been nearly a year since I posted that one. Must be getting old. Thanks Nukey for the info! Quote Link to comment Share on other sites More sharing options...
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