A source code rewrite to the 1982 arcade game
Source code rewrite by SynaMax, started January 25th, 2024; complete ROM set rebuilt for the first time on January 29, 2024
Game Designer: John Newcomer
Main Programmer: Bill Pfutzenreuter
Other Programmers: Cary Kolker and Ken Lantz
Sound ROM (VSNDRM4) main programmers: John Kotlarik and Tim Murphy
The original source code for the game can be found at https://github.com/historicalsource/joust/
For the first time ever, the source code for the sound ROM is included with the game code. The original sound ROM source can be found here: https://github.com/historicalsource/williams-soundroms/blob/main/VSNDRM4.SRC
- 06/24/2024 - I recently discovered that back in February, Macro Assembler {AS} version 1.42 Build 262 changed the way it handles 6809 instructions that use an empty first argument on indexed address expressions (i.e. using LDA X instead of LDA ,X). This syntax is used extensively throughout the codebase and now results in errors when trying to build the game. A new instruction specific to AS has been inserted in the MAKE.ASM file to fix this issue.
- 02/08/2024 - The first mod for Joust has been added! Originally written in 2008 and found on Coinoplove.com, this is a pause mod that allows the player 1 button to act as a pause button during gameplay. Thanks to braedel for bringing this cool hack to my attention. To enable the mod, simply remove the semi-colon in front of the
PauseMod EQU 1define inmake.ASM. - 01/30/2024 - After MONTHS of trying to figure out how to get Tim Murphy's Walsh Function Sound Machine macros to work, I finally succeeded in producing the correct binary data that matches up with the sound ROM. This is huge as this also applies to Sinistar's sound ROM as well. In layman's terms, this means we can accurately rebuild the data for the "Pterodactyl Scream" and "Ostrich Skid" sound effects exactly as how it was done in 1982!
- 01/29/2024 (Cont'd) - ROM 12 and Video Sound ROM 4 are complete! The entire game is completely rebuildable now!
- 01/29/2024 - ROMs 1 through 11 ($0000-$EFFF) for Joust now match up perfectly! All that remains is the sound rom and Test ROM ($F000).
- 01/27/2024 - The rewritten code now assembles up to address $5ED0 and matches up perfectly with the first six ROMs for the game. This includes all the sprite images for every game object, the message display routines, font sprites, and all the strings. The game program itself is up next and exists entirely in one file that's over 8000 lines of code. This is going to take a while to rewrite. It's going to be a bit of a challenge without any pre-existing equates listing but I have a disassembly of the game to help out.
- 01/25/2024 - Starting rewriting Joust's code today. Already got all the sprites to assemble with Macroassembler {AS}...that's almost the first four ROMs!
This source code was rewritten to target Macro Assembler {AS}.
To build Joust, place the ASL and P2BIN executables in the same directory with all the source files from the repository.
Then, open a command prompt and type in:
asl make.asm -o joust.pOnce the joust.p file is generated, we can use the BURN.BAT file to create the 12 separate ROM files that make up Joust.
| Address | ROM # | MAME ROM set Filename |
|---|---|---|
| 0000-0FFF | ROM 1 | joust_rom_1b_3006-13.e4 |
| 1000-1FFF | ROM 2 | joust_rom_2b_3006-14.c4 |
| 2000-2FFF | ROM 3 | joust_rom_3b_3006-15.a4 |
| 3000-3FFF | ROM 4 | joust_rom_4b_3006-16.e5 |
| 4000-4FFF | ROM 5 | joust_rom_5b_3006-17.c5 |
| 5000-5FFF | ROM 6 | joust_rom_6b_3006-18.a5 |
| 6000-6FFF | ROM 7 | joust_rom_7b_3006-19.e6 |
| 7000-7FFF | ROM 8 | joust_rom_8b_3006-20.c6 |
| 8000-8FFF | ROM 9 | joust_rom_9b_3006-21.a6 |
| 9000-CFFF | (SPACE RESERVED FOR RAM) | |
| D000-DFFF | ROM 10 | joust_rom_10b_3006-22.a7 |
| E000-EFFF | ROM 11 | joust_rom_11b_3006-23.c7 |
| F000-FFFF | ROM 12 | joust_rom_12b_3006-24.e7 |
If it's not possible to use BURN.BAT, this can be typed into a command prompt instead:
p2bin joust.p joust_rom_1b_3006-13.e4 -l 00 -r $0000-$0FFF
p2bin joust.p joust_rom_2b_3006-14.c4 -l 00 -r $1000-$1FFF
p2bin joust.p joust_rom_3b_3006-15.a4 -l 00 -r $2000-$2FFF
p2bin joust.p joust_rom_4b_3006-16.e5 -l 00 -r $3000-$3FFF
p2bin joust.p joust_rom_5b_3006-17.c5 -l 00 -r $4000-$4FFF
p2bin joust.p joust_rom_6b_3006-18.a5 -l 00 -r $5000-$5FFF
p2bin joust.p joust_rom_7b_3006-19.e6 -l 00 -r $6000-$6FFF
p2bin joust.p joust_rom_8b_3006-20.c6 -l 00 -r $7000-$7FFF
p2bin joust.p joust_rom_9b_3006-21.a6 -l 00 -r $8000-$8FFF
p2bin joust.p joust_rom_10b_3006-22.a7 -l 00 -r $D000-$DFFF
p2bin joust.p joust_rom_11b_3006-23.c7 -l 00 -r $E000-$EFFF
p2bin joust.p joust_rom_12b_3006-24.e7 -l 00 -r $F000-$FFFFBuilding Video Sound Rom 4 (VSNDRM4) just requires two commands:
asl VSNDRM4.ASM -o vsndrm4.pThen use P2BIN to generate the binary ROM file:
p2bin vsndrm4.p video_sound_rom_4_std_780.ic12 -l 00 -r $F000-$FFFFThis is probably a little bit overkill but I also included code that builds the required decoder ROMs needed for the game to run. MAME will refuse to launch the game if these files are not included so I added a new source file, even though it's fairly easy to find these files online. Regardless, I added them for completeness sake.
Following Defender, Robotron, and Sinistar, Joust is the latest Williams Electronics arcade game to have its source code retargeted for a newer assembler. Because Sinistar and Joust's codebases contain a lot of similarities, I am reusing Macroassembler {AS} as the new assembler to build this game. It appears that the same Boston System Office (BSO) assembler used for Sinistar, was previously utilized for Joust as well.
Sinistar's codebase - while more complex and featuring way more source files - also came with EQU and SET files that were extremely helpful in mapping out all the symbols and their addresses. We don't have this luxury with Joust's code unfortunately. To get around this, a disassembly of the game was generated from MAME and used whenever I was stuck.
Fortunately, the code for the game is fairly straight-forward as it doesn't heavily rely on macros (unlike Sinistar) and required much less rewriting. For example, Sinistar took a little over 3 months to figure out, while rewriting Joust took just 4 days (though a lot of that time during the Sinistar rewrite was attributed to figuring out how to change the old syntax and expressions over to the newer assembler).
I also chose not to rewrite the original three previous versions of Joust, even though they are included in the original codebase. Maybe I'll get to them one day, but for now it's not as important as getting the final version of the game up and running.
Whenever possible, any changes to the code are marked by comments to the right that say ;;Fixme was: followed by the original instructions.
IF PNBR-* > 0 ;;Fixme was: IFGT PNBR-*
{AS} has some quirks with local labels so I had to redo them. For example, here's what local labels look like for the BSO assembler:
1$ lda lol
jmp 2$
2$ lda lmao
This is what this code would look like rewritten for {AS}:
.1S lda lol
jmp .2S
.2S lda lmao
Not all local label changes have been marked with ;;Fixme was: comments as it would be too many to add and can clutter up the code.
There are several symbols in both Sinistar and Joust that use dollar signs. $ are reserved for hex numbers only in {AS} so these labels/symbols have been renamed, by replacing the $ with an S.
Thankfully, I found some documentation for another missing BSO assembler that explains some of the syntax and expressions used in the original source code. Here are some important ones to point out:
UNARY: + Identity
- Negation
> High byte
< Low byte
!N Logical one's complement
BINARY: + Addition
- Subtraction
* Multiplication
/ Division. Any remainder is discarded.
!. Logical AND
!+ Logical OR
!X Logical Exclusive OR
Expressions will be evaluated according to the following operator
precedence, and from left to right when of equal precedence:
1) Unary +, unary -, !N, <, >
2) *, /, !., !+, !X
3) Binary +, binary -
Pseudo- Syntax Condition tested
op
.IF .IF logical expr true
.IF .IF expr expr <> 0
.IFE .IFE expr expr = 0
.IFN .IFN expr expr <> 0
.IFLT .IFLT expr expr < 0
.IFGT .IFGT expr expr > 0
.IFLE .IFLE expr expr <= 0
.IFGE .IFGE expr expr >= 0
.IFDEF .IFDEF sym sym is a defined symbol
.IFNDEF .IFNDEF sym sym is an undefined symbol
.IFB .IFB <string> string is blank
.IFNB .IFNB <string> string is not blank
.IFIDN .IFIDN <str1>,<str2> str1 and str2 are identical
character strings
.IFNIDN .IFNIDN <str1>,<str2> str1 and str2 are not
identical
These conditional pseudo-ops get used a lot so having this guide was extremely important for getting macros to work with Macroassembler {AS}.
Interestingly, there are a couple of new expressions that don't appear here that do show up in the codebase:
FCB WAIT,!HCALL,!WCALL,MINUS-*,ZERO-*,PLUS-*,FLYVEL
!H was used for separating the high byte of a word, while !W is used for the lower byte of a word. The first one does show up occasionally in Sinistar's codebase but !W is a new one that I haven't encountered before.
- Exclusive OR
!Xare now just!. - Bit shift operators
!<and!>are now<<and>>. #!N4is a value used a lot for fixing a DMA bug for the blitter graphic chip. This value has been replaced with#~$4.- Binary AND
!.are now just& - Binary OR
!+are now| *asterisks were used to denote comments at the start of a new line. These have now have semi-colons in front of them (;*) to tell the assembler this is a comment.*is now exclusively used as the current value of the program counter.
Sinistar's codebase contains a plethora of inconsistent label names thanks to the small symbol table size of the BSO assembler. Fortunately, there is only one occurrence of this issue, where TBRIDGE was truncated to TBRIDG. The original define in JOUSTRV4.ASM now reflects the full name.