BBC Micro cassette Elite | BBC Micro disc Elite | Acorn Electron Elite | 6502 Second Processor Elite | Commodore 64 Elite | Apple II Elite | BBC Master Elite | NES Elite | Elite-A | Teletext Elite | Elite Universe Editor | Elite Compendium (BBC Master) | Elite Compendium (BBC Micro) | Elite over Econet | Flicker-free Commodore 64 Elite | BBC Micro Aviator | BBC Micro Revs | Archimedes Lander
This repository contains the original source code for Elite on the Apple II, with every single line documented and (for the most part) explained. It is literally the original source code, just heavily commented.
It is a companion to the elite.bbcelite.com website.
See the introduction for more information, or jump straight into the documented source code.
This repository contains the original source code for Elite on the Apple II, with every single line documented and (for the most part) explained.
You can build the fully functioning game from this source. Five variants are currently supported: the 4am crack disk, the game disk from Ian Bell's personal website, the variant built by the source disk build process, the variant built from the CODE* binary files already on the source disk, and the variant built from the ELT* binary files already on the source disk.
This repository is a companion to the elite.bbcelite.com website, which contains all the code from this repository, but laid out in a much more human-friendly fashion. The links at the top of this page will take you to repositories for the other versions of Elite that are covered by this project.
-
If you want to browse the source and read about how Elite works under the hood, you will probably find the website a better place to start than this repository.
-
If you would rather explore the source code in your favourite IDE, then the annotated source is what you're looking for. It contains the exact same content as the website, so you won't be missing out (the website is generated from the source files, so they are guaranteed to be identical). You might also like to read the section on browsing the source in an IDE for some tips.
-
If you want to build Apple II Elite from the source on a modern computer, to produce a working game disk that can be loaded into an Apple II or an emulator, then you want the section on building Apple II Elite from the source.
My hope is that this repository and the accompanying website will be useful for those who want to learn more about Elite and what makes it tick. It is provided on an educational and non-profit basis, with the aim of helping people appreciate one of the most iconic games of the 8-bit era.
Apple II Elite was written by Ian Bell and David Braben and is copyright © D. Braben and I. Bell 1986.
The code on this site is identical to the source disks released on Ian Bell's personal website (it's just been reformatted to be more readable).
The commentary is copyright © Mark Moxon. Any misunderstandings or mistakes in the documentation are entirely my fault.
Huge thanks are due to the original authors for not only creating such an important piece of my childhood, but also for releasing the source code for us to play with. Also, a big thumbs up to Andy McFadden for his excellent disassembly of Elite for the Apple II, which is a really useful reference for anyone exploring the Apple II binaries.
The following archives from Ian Bell's personal website form the basis for this project:
This repository is not provided with a licence, and there is intentionally no LICENSE file provided.
According to GitHub's licensing documentation, this means that "the default copyright laws apply, meaning that you retain all rights to your source code and no one may reproduce, distribute, or create derivative works from your work".
The reason for this is that my commentary is intertwined with the original Elite source code, and the original source code is copyright. The whole site is therefore covered by default copyright law, to ensure that this copyright is respected.
Under GitHub's rules, you have the right to read and fork this repository... but that's it. No other use is permitted, I'm afraid.
My hope is that the educational and non-profit intentions of this repository will enable it to stay hosted and available, but the original copyright holders do have the right to ask for it to be taken down, in which case I will comply without hesitation. I do hope, though, that along with the various other disassemblies and commentaries of this source, it will remain viable.
If you want to browse the source in an IDE, you might find the following useful.
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The most interesting files are in the main-sources folder:
- The main game's source code is in the elite-source.asm and elite-data.asm files (containing the game code and game data respectively) - this is the motherlode and probably contains all the stuff you're interested in.
-
It's probably worth skimming through the notes on terminology and notations on the accompanying website, as this explains a number of terms used in the commentary, without which it might be a bit tricky to follow at times (in particular, you should understand the terminology I use for multi-byte numbers).
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The accompanying website contains a number of "deep dive" articles, each of which goes into an aspect of the game in detail. Routines that are explained further in these articles are tagged with the label
Deep dive:and the relevant article name. -
There are loads of routines and variables in Elite - literally hundreds. You can find them in the source files by searching for the following:
Type: Subroutine,Type: Variable,Type: WorkspaceandType: Macro. -
If you know the name of a routine, you can find it by searching for
Name: <name>, as inName: SCAN(for the 3D scanner routine) orName: LL9(for the ship-drawing routine). -
The entry point for the main game code is routine
BEGIN, which you can find by searching forName: BEGIN. If you want to follow the program flow all the way from the title screen around the main game loop, then you can find a number of deep dives on program flow on the accompanying website. -
The source code is designed to be read at an 80-column width and with a monospaced font, just like in the good old days.
I hope you enjoy exploring the inner workings of Commmodore 64 Elite as much as I have.
There are five main folders in this repository, which reflect the order of the build process.
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1-source-files contains all the different source files, such as the main assembler source files, image binaries, fonts, boot files and so on.
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2-build-files contains build-related scripts, such as the checksum, encryption and crc32 verification scripts.
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3-assembled-output contains the output from the assembly process, when the source files are assembled and the results processed by the build files.
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4-reference-binaries contains the correct binaries for each variant, so we can verify that our assembled output matches the reference.
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5-compiled-game-disks contains the final output of the build process: a DSK disk image that contains the compiled game and which can be run on real hardware or in an emulator.
Builds are supported for both Windows and Mac/Linux systems. In all cases the build process is defined in the Makefile provided.
You will need the following to build Apple II Elite from the source:
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BeebAsm, which can be downloaded from the BeebAsm repository. Mac and Linux users will have to build their own executable with
make code, while Windows users can just download thebeebasm.exefile. -
Python. The build process has only been tested on 3.x, but 2.7 might work.
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diskm8, which can be downloaded from the diskm8 repository.
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Mac and Linux users may need to install
makeif it isn't already present (for Windows users,make.exeis included in this repository).
You may be wondering why we're using BeebAsm - a BBC Micro assembler - to build the Apple II version of Elite. This is because Apple II Elite is a conversion of 6502 Second Processor Elite, which itself is a direct descendant of the original 1984 release for the BBC Micro and Acorn Electron (and the same is true of the Commodore 64 and NES versions of Elite - they are all cut from the same cloth). The NES version aside, all of the 6502 versions of Elite were built and assembled on a BBC Micro, including the Commodore and Apple versions, so BeebAsm is a good modern assembler to use for the Apple II version as well.
For details of how the build process works, see the build documentation on bbcelite.com.
Let's look at how to build Apple II Elite from the source.
For Windows users, there is a batch file called make.bat which you can use to build the game. Before this will work, you should edit the batch file and change the values of the BEEBASM, PYTHON and DISKM8 variables to point to the locations of your beebasm.exe, python.exe and diskm8.exe executables. You also need to change directory to the repository folder (i.e. the same folder as make.bat).
All being well, entering the following into a command window:
make.bat
will produce a file called elite-apple-4am-crack.dsk in the 5-compiled-game-disks folder that contains the 4am crack variant, which you can then load into an emulator, or into a real Apple II.
The build process uses a standard GNU Makefile, so you just need to install make if your system doesn't already have it. If BeebAsm, Python or diskm8 are not on your path, then you can either fix this, or you can edit the Makefile and change the BEEBASM, PYTHON and DISKM8 variables in the first three lines to point to their locations. You also need to change directory to the repository folder (i.e. the same folder as Makefile).
All being well, entering the following into a terminal window:
make
will produce a file called elite-apple-4am-crack.dsk in the 5-compiled-game-disks folder that contains the 4am crack variant, which you can then load into an emulator, or into a real Apple II.
By default the build process will create a typical Elite game disk with a standard commander and verified binaries. There are various arguments you can pass to the build to change how it works. They are:
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variant=<name>- Build the specified variant:variant=4am-crack(default)variant=ib-diskvariant=source-disk-buildvariant=source-disk-code-filesvariant=source-disk-elt-files
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commander=max- Start with a maxed-out commander (specifically, this is the test commander file from the original source, which is almost but not quite maxed-out) -
encrypt=no- Disable encryption and checksum routines -
match=no- Do not attempt to match the original game binaries (i.e. omit workspace noise) -
verify=no- Disable crc32 verification of the game binaries
So, for example:
make variant=source-disk-build commander=max encrypt=no match=no verify=no
will build an unencrypted source disk variant with a maxed-out commander, no workspace noise and no crc32 verification.
The unencrypted version should be more useful for anyone who wants to make modifications to the game code. As this argument produces unencrypted files, the binaries produced will be quite different to the binaries on the original source disk, which are encrypted.
See below for more on the verification process.
If you change the source code in any way, you may break the game; if so, it will typically hang at the loading screen, though in some versions it may hang when launching from the space station.
To fix this, you may need to update some of the hard-coded addresses in the checksum script so that they match the new addresses in your changed version of the code. See the comments in the elite-checksum.py script for details.
The default build process prints out checksums of all the generated files, along with the checksums of the files from the original sources. You can disable verification by passing verify=no to the build.
The Python script crc32.py in the 2-build-files folder does the actual verification, and shows the checksums and file sizes of both sets of files, alongside each other, and with a Match column that flags any discrepancies. If you are building an unencrypted set of files then there will be lots of differences, while the encrypted files should mostly match (see the Differences section below for more on this).
The binaries in the 4-reference-binaries folder are those extracted from the released version of the game, while those in the 3-assembled-output folder are produced by the build process. For example, if you don't make any changes to the code and build the project with make, then this is the output of the verification process:
Results for variant: 4am-crack
[--originals--] [---output----]
Checksum Size Checksum Size Match Filename
-----------------------------------------------------------
796a263b 32768 796a263b 32768 Yes CODE.unprot.bin
62271826 20480 62271826 20480 Yes CODE1.bin
a6f4ed53 20480 a6f4ed53 20480 Yes CODE1.unprot.bin
f7b5430f 12288 f7b5430f 12288 Yes CODE2.bin
35bc6507 12288 35bc6507 12288 Yes CODE2.unprot.bin
a831e7e2 5280 a831e7e2 5280 Yes DATA.bin
e66e6208 5280 e66e6208 5280 Yes DATA.unprot.bin
4520e38d 26400 4520e38d 26400 Yes ELA.bin
62271826 20480 62271826 20480 Yes ELB.bin
6adb264a 3710 6adb264a 3710 Yes ELTA.bin
711df275 2363 711df275 2363 Yes ELTB.bin
c4da2495 3082 c4da2495 3082 Yes ELTC.bin
dc6bf353 3308 dc6bf353 3308 Yes ELTD.bin
88396ce4 2243 88396ce4 2243 Yes ELTE.bin
5ebd3212 3477 5ebd3212 3477 Yes ELTF.bin
fef23147 2391 fef23147 2391 Yes ELTG.bin
cb094bf3 1203 cb094bf3 1203 Yes ELTH.bin
0196f101 306 0196f101 306 Yes ELTI.bin
978e5515 1437 978e5515 1437 Yes ELTJ.bin
3d92a08d 1824 3d92a08d 1824 Yes ELTK.bin
d61caafe 3513 d61caafe 3513 Yes IANTOK.bin
de4a0b89 1274 de4a0b89 1274 Yes SEC3.bin
6a113fb1 7314 6a113fb1 7314 Yes SHIPS.bin
f77b2a55 992 f77b2a55 992 Yes WORDS.bin
- - c22cea95 41 - MOVER.bin
All the compiled binaries match the originals, so we know we are producing the same final game as the 4am crack variant.
During compilation, details of every step are output in a file called compile.txt in the 3-assembled-output folder. If you have problems, it might come in handy, and it's a great reference if you need to know the addresses of labels and variables for debugging (or just snooping around).
This repository contains the source code for four different variants of Apple II Elite:
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The 4am crack, which is the most authentic version of the original Firebird game (only the disk protection has been removed, and I have also removed the CTRL-E characters from the filenames on the original disk to make the the modern build process simpler)
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The game disk from Ian Bell's personal website, which contains a cracked version of the original Firebird game by The Student
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The variant produced by running the build process on the source disk from Ian Bell's personal website
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The variant produced using the CODE* binaries from the source disk on Ian Bell's personal website, which differ slightly from the binaries that are produced by running the build process
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The variant produced using the ELT* binaries from the source disk on Ian Bell's personal website, which differ slightly from the binaries that are produced by running the build process
By default the build process builds the FirebIan Bell game disk variant, but you can build a specified variant using the variant= build parameter.
You can add variant=4am-crack to produce the elite-apple-4am-crack.dsk file that contains the 4am crack variant, though that's the default value so it isn't necessary. In other words, you can build it like this:
make.bat variant=4am-crack
or this on a Mac or Linux:
make variant=4am-crack
This will produce a file called elite-apple-4am-crack.dsk in the 5-compiled-game-disks folder that contains the 4am crack variant.
The verification checksums for this version are as follows:
Results for variant: 4am-crack
[--originals--] [---output----]
Checksum Size Checksum Size Match Filename
-----------------------------------------------------------
796a263b 32768 796a263b 32768 Yes CODE.unprot.bin
62271826 20480 62271826 20480 Yes CODE1.bin
a6f4ed53 20480 a6f4ed53 20480 Yes CODE1.unprot.bin
f7b5430f 12288 f7b5430f 12288 Yes CODE2.bin
35bc6507 12288 35bc6507 12288 Yes CODE2.unprot.bin
a831e7e2 5280 a831e7e2 5280 Yes DATA.bin
e66e6208 5280 e66e6208 5280 Yes DATA.unprot.bin
4520e38d 26400 4520e38d 26400 Yes ELA.bin
62271826 20480 62271826 20480 Yes ELB.bin
6adb264a 3710 6adb264a 3710 Yes ELTA.bin
711df275 2363 711df275 2363 Yes ELTB.bin
c4da2495 3082 c4da2495 3082 Yes ELTC.bin
dc6bf353 3308 dc6bf353 3308 Yes ELTD.bin
88396ce4 2243 88396ce4 2243 Yes ELTE.bin
5ebd3212 3477 5ebd3212 3477 Yes ELTF.bin
fef23147 2391 fef23147 2391 Yes ELTG.bin
cb094bf3 1203 cb094bf3 1203 Yes ELTH.bin
0196f101 306 0196f101 306 Yes ELTI.bin
978e5515 1437 978e5515 1437 Yes ELTJ.bin
3d92a08d 1824 3d92a08d 1824 Yes ELTK.bin
d61caafe 3513 d61caafe 3513 Yes IANTOK.bin
c22cea95 41 c22cea95 41 Yes MOVER.bin
de4a0b89 1274 de4a0b89 1274 Yes SEC3.bin
6a113fb1 7314 6a113fb1 7314 Yes SHIPS.bin
f77b2a55 992 f77b2a55 992 Yes WORDS.bin
You can build the Ian Bell game disk variant by appending variant=ib-disk to the make command, like this on Windows:
make.bat variant=ib-disk
or this on a Mac or Linux:
make variant=ib-disk
This will produce a file called elite-apple-ib-disk.dsk in the 5-compiled-game-disks folder that contains the Ian Bell game disk variant.
The verification checksums for this version are as follows:
Results for variant: ib-disk
[--originals--] [---output----]
Checksum Size Checksum Size Match Filename
-----------------------------------------------------------
dcd37bb9 32768 dcd37bb9 32768 Yes CODE.unprot.bin
310a5ea5 20480 310a5ea5 20480 Yes CODE1.bin
310a5ea5 20480 310a5ea5 20480 Yes CODE1.unprot.bin
35bc6507 12288 35bc6507 12288 Yes CODE2.bin
35bc6507 12288 35bc6507 12288 Yes CODE2.unprot.bin
18be5848 5376 18be5848 5376 Yes DATA.bin
18be5848 5376 18be5848 5376 Yes DATA.unprot.bin
c41f1c49 26112 c41f1c49 26112 Yes ELA.bin
310a5ea5 20480 310a5ea5 20480 Yes ELB.bin
1bbcc440 3710 1bbcc440 3710 Yes ELTA.bin
5125fc56 2363 5125fc56 2363 Yes ELTB.bin
c4da2495 3082 c4da2495 3082 Yes ELTC.bin
dc6bf353 3308 dc6bf353 3308 Yes ELTD.bin
88396ce4 2243 88396ce4 2243 Yes ELTE.bin
4c6071c1 3477 4c6071c1 3477 Yes ELTF.bin
fef23147 2391 fef23147 2391 Yes ELTG.bin
cb094bf3 1203 cb094bf3 1203 Yes ELTH.bin
0196f101 306 0196f101 306 Yes ELTI.bin
978e5515 1437 978e5515 1437 Yes ELTJ.bin
3d92a08d 1824 3d92a08d 1824 Yes ELTK.bin
d61caafe 3513 d61caafe 3513 Yes IANTOK.bin
c22cea95 41 c22cea95 41 Yes MOVER.bin
6a113fb1 7314 6a113fb1 7314 Yes SHIPS.bin
f77b2a55 992 f77b2a55 992 Yes WORDS.bin
- - de4a0b89 1274 - SEC3.bin
You can build the source disk build variant by appending variant=source-disk-build to the make command, like this on Windows:
make.bat variant=source-disk-build
or this on a Mac or Linux:
make variant=source-disk-build
This does not currently produce a game disk, but instead produces the same binaries as the original build process. In the original development system, these files would then be transmitted from the BBC Micro to the Apple II via a serial link, but that setup isn't emulated here.
The verification checksums for this version are as follows:
Results for variant: source-disk-build
[--originals--] [---output----]
Checksum Size Checksum Size Match Filename
-----------------------------------------------------------
b997aacf 32768 b997aacf 32768 Yes CODE.unprot.bin
3b881cde 20480 3b881cde 20480 Yes CODE1.bin
fa257f9a 20480 fa257f9a 20480 Yes CODE1.unprot.bin
5cc4867f 12288 5cc4867f 12288 Yes CODE2.bin
05dbc169 12288 05dbc169 12288 Yes CODE2.unprot.bin
2aa536de 5280 2aa536de 5280 Yes DATA.bin
fca02798 5280 fca02798 5280 Yes DATA.unprot.bin
b4a81200 26112 b4a81200 26112 Yes ELA.bin
3b881cde 20480 3b881cde 20480 Yes ELB.bin
9d14b02b 3705 9d14b02b 3705 Yes ELTA.bin
2a02c544 2364 2a02c544 2364 Yes ELTB.bin
99d1fd8c 3083 99d1fd8c 3083 Yes ELTC.bin
81b3f0d7 3318 81b3f0d7 3318 Yes ELTD.bin
0354ad31 2222 0354ad31 2222 Yes ELTE.bin
a23ed383 3474 a23ed383 3474 Yes ELTF.bin
d024488b 2391 d024488b 2391 Yes ELTG.bin
d251e768 1203 d251e768 1203 Yes ELTH.bin
e9b436ce 306 e9b436ce 306 Yes ELTI.bin
1375d27d 1437 1375d27d 1437 Yes ELTJ.bin
e878870b 1805 e878870b 1805 Yes ELTK.bin
d61caafe 3513 d61caafe 3513 Yes IANTOK.bin
6a113fb1 7314 6a113fb1 7314 Yes SHIPS.bin
998bb35a 992 998bb35a 992 Yes WORDS.bin
- - da873557 41 - MOVER.bin
- - de4a0b89 1274 - SEC3.bin
You can build the source disk code files variant by appending variant=source-disk-code-files to the make command, like this on Windows:
make.bat variant=source-disk-code-files
or this on a Mac or Linux:
make variant=source-disk-code-files
This does not currently produce a game disk, but instead produces the CODE* binary files that can be found on the source disk. In the original development system, these files would then be transmitted from the BBC Micro to the Apple II via a serial link, but that setup isn't emulated here.
The verification checksums for this version are as follows:
Results for variant: source-disk-code-files
[--originals--] [---output----]
Checksum Size Checksum Size Match Filename
-----------------------------------------------------------
a127520f 32768 a127520f 32768 Yes CODE.unprot.bin
1f041708 20480 1f041708 20480 Yes CODE1.bin
6ad3ef26 20480 6ad3ef26 20480 Yes CODE1.unprot.bin
f64fb5c3 12288 f64fb5c3 12288 Yes CODE2.bin
582607aa 12288 582607aa 12288 Yes CODE2.unprot.bin
a831e7e2 5280 a831e7e2 5280 Yes DATA.bin
e66e6208 5280 e66e6208 5280 Yes DATA.unprot.bin
6f2ca4e7 26112 6f2ca4e7 26112 Yes ELA.bin
1f041708 20480 1f041708 20480 Yes ELB.bin
3f274135 3709 3f274135 3709 Yes ELTA.bin
31d0c63b 2364 31d0c63b 2364 Yes ELTB.bin
93630390 3083 93630390 3083 Yes ELTC.bin
7d92f313 3318 7d92f313 3318 Yes ELTD.bin
daa83532 2252 daa83532 2252 Yes ELTE.bin
e867f67f 3471 e867f67f 3471 Yes ELTF.bin
a0d360a1 2391 a0d360a1 2391 Yes ELTG.bin
edf8f5cf 1203 edf8f5cf 1203 Yes ELTH.bin
b48b8c0a 306 b48b8c0a 306 Yes ELTI.bin
ba7ba5ea 1437 ba7ba5ea 1437 Yes ELTJ.bin
f7446a16 1809 f7446a16 1809 Yes ELTK.bin
d61caafe 3513 d61caafe 3513 Yes IANTOK.bin
6a113fb1 7314 6a113fb1 7314 Yes SHIPS.bin
f77b2a55 992 f77b2a55 992 Yes WORDS.bin
- - da873557 41 - MOVER.bin
- - de4a0b89 1274 - SEC3.bin
You can build the source disk code files variant by appending variant=source-disk-elt-files to the make command, like this on Windows:
make.bat variant=source-disk-elt-files
or this on a Mac or Linux:
make variant=source-disk-elt-files
This does not currently produce a game disk, but instead produces the ELT* binary files that can be found on the source disk. In the original development system, these files would then be transmitted from the BBC Micro to the Apple II via a serial link, but that setup isn't emulated here.
The verification checksums for this version are as follows:
Results for variant: source-disk-elt-files
[--originals--] [---output----]
Checksum Size Checksum Size Match Filename
-----------------------------------------------------------
b8b7a1cc 32768 b8b7a1cc 32768 Yes CODE.unprot.bin
3b881cde 20480 3b881cde 20480 Yes CODE1.bin
fa257f9a 20480 fa257f9a 20480 Yes CODE1.unprot.bin
2524d466 12288 2524d466 12288 Yes CODE2.bin
04fbca6a 12288 04fbca6a 12288 Yes CODE2.unprot.bin
a831e7e2 5280 a831e7e2 5280 Yes DATA.bin
e66e6208 5280 e66e6208 5280 Yes DATA.unprot.bin
bc47c542 26112 bc47c542 26112 Yes ELA.bin
3b881cde 20480 3b881cde 20480 Yes ELB.bin
9d14b02b 3705 9d14b02b 3705 Yes ELTA.bin
2a02c544 2364 2a02c544 2364 Yes ELTB.bin
99d1fd8c 3083 99d1fd8c 3083 Yes ELTC.bin
81b3f0d7 3318 81b3f0d7 3318 Yes ELTD.bin
0354ad31 2222 0354ad31 2222 Yes ELTE.bin
a23ed383 3474 a23ed383 3474 Yes ELTF.bin
d024488b 2391 d024488b 2391 Yes ELTG.bin
d251e768 1203 d251e768 1203 Yes ELTH.bin
e9b436ce 306 e9b436ce 306 Yes ELTI.bin
1375d27d 1437 1375d27d 1437 Yes ELTJ.bin
e878870b 1805 e878870b 1805 Yes ELTK.bin
d61caafe 3513 d61caafe 3513 Yes IANTOK.bin
6a113fb1 7314 6a113fb1 7314 Yes SHIPS.bin
f77b2a55 992 f77b2a55 992 Yes WORDS.bin
- - da873557 41 - MOVER.bin
- - de4a0b89 1274 - SEC3.bin
You can see the differences between the variants by searching the source code for _IB_DISK (for features in the Ian Bell game disk variant), _SOURCE_DISK_BUILD (for features in the source disk build variant), _SOURCE_DISK_CODE_FILES (for features in the source disk CODE files variant) or _SOURCE_DISK_ELT_FILES (for features in the source disk ELT files variant). You can also search for _SOURCE_DISK for features in all the source disk variants.
The main differences in the Ian Bell game disk variant compared to the 4am crack variant are:
-
The loading screen is different, showing "Cracked by The Student" instead of the Firebird logo.
-
The values of some of the variables have been changed from the placeholder values in the source code, as the game was cracked by extracting it from memory while the game was running.
The main differences in the three source disk variants compared to the 4am crack variant are:
-
The values of the STORE and CODE2 configuration variables are different, so the game copies CODE2 out of bank-switched RAM when it starts.
-
There is an extra CLD instruction on starting the game.
-
The game uses JSR DOXC to move the text cursor to a specified column, while the released game uses STA XC.
-
The game uses JSR DOYC to move the text cursor to a specified row, while the released game uses STA YC.
-
The game uses JSR INCYC to move the text cursor to the next row, while the released game uses INC YC.
-
The "J", "K", "M" and "I" key presses for moving the chart crosshairs are not supported.
-
The game waits for the vertical sync to implement pauses, while the released game just performs loop iterations.
-
The default setting is to display both upper and lower case letters, while the default for the released game is upper case only.
-
The joystick modification is missing from the end of S%, so the game will still scan the joystick fire button, even if joysticks are not configured.
-
"M" and "J" can still be pressed when the charts are showing.
-
The joystick fire button can be used to configure joysticks from the title screen.
-
If the energy bomb is already going off and we press "B", the effect restarts.
Further differences in the source disk build variant compared to the 4am crack variant are:
- The dashboard has a blue rim and different coloured labels to the released version, and the loading screen has the date "23 SEPT 1985" printed in the space view.
Further differences in the source disk CODE files variant compared to the 4am crack variant are:
-
The dashboard has a blue rim and different coloured labels to the released version, and the loading screen has the date "7 SEPT 1985" printed in the space view.
-
It contains the code to cope with phantom key presses from the Commodore 64 version.
-
The Thargoid spawning logic is different.
-
There's some unused code that would speed up chart crosshair movement when fire is pressed.
-
The joystick is not disabled while the docking computer is activated.
Further differences in the source disk ELT files variant compared to the 4am crack variant are:
- The dashboard has a blue rim and different coloured labels to the released version, and the loading screen has the date "7 SEPT 1985" printed in the space view.
See the accompanying website for a comprehensive list of differences between the variants.
Instead of initialising workspaces with null values like BeebAsm, the original BBC Micro source code creates its workspaces by simply incrementing the P% and O% program counters, which means that the workspaces end up containing whatever contents the allocated memory had at the time. As the source files are broken into multiple BBC BASIC programs that run each other sequentially, this means the workspaces in the source code tend to contain either fragments of these BBC BASIC source programs, or assembled code from an earlier stage. This doesn't make any difference to the game code, which either initialises the workspaces at runtime or just ignores their initial contents, but if we want to be able to produce byte-accurate binaries from the modern BeebAsm assembly process, we need to include this "workspace noise" when building the project. Workspace noise is only loaded by the encrypt target; for the build target, workspaces are initialised with zeroes.
You can disable the production of byte-accurate binaries by passing match=no to the build. This will omit most workspace noise, leaving workspaces initialised with zeroes instead.
Here's an example of how workspace noise is included, from the big code file in elite-bcfs.asm:
IF _MATCH_ORIGINAL_BINARIES
IF _IB_DISK OR _4AM_CRACK
EQUB &00, &5C, &A0, &6C, &73, &73, &31, &00
EQUB &90, &20, &B8, &00, &00, &A9, &9F, &52
EQUB &35, &00, &90, &20, &C0, &00, &00, &BE
EQUB &9F, &52, &37, &00, &90, &20, &CB, &00
EQUB &00, &28, &A1, &48, &50, &52, &00, &90
EQUB &20, &E6, &00, &00, &CC, &9F, &52, &61
EQUB &66, &74, &65, &72, &00, &90, &20, &F4
EQUB &00, &00, &D7, &9F, &52, &58, &32, &00
EQUB &90, &21, &00, &00, &00, &E2, &9F, &52
EQUB &58, &31, &00, &90, &21, &04, &00, &00
EQUB &EC, &9F, &52, &31, &00, &90, &21, &0C
EQUB &00, &00, &F6, &9F, &52, &61, &00, &90
EQUB &21, &17, &00, &00, &00, &A0, &52, &36
EQUB &00, &90, &21, &30, &00, &00
ELIF _SOURCE_DISK_BUILD
EQUB &52, &00, &90, &20, &CB, &00, &00, &A7
EQUB &9F, &52, &61, &66, &74, &65, &72, &00
EQUB &90, &20, &D9, &00, &00, &B2, &9F, &52
EQUB &58, &32, &00, &90, &20, &E5, &00, &00
EQUB &BD, &9F, &52, &58, &31, &00, &90, &20
EQUB &E9, &00, &00, &C7, &9F, &52, &31, &00
EQUB &90, &20, &F1, &00, &00, &D1, &9F, &52
EQUB &61, &00, &90, &20, &FC, &00, &00, &DB
EQUB &9F, &52, &36, &00, &90, &21, &15, &00
EQUB &00, &F2, &9F, &52, &34, &00, &90, &21
EQUB &17, &00, &00, &FC, &9F, &65, &74, &74
EQUB &65, &72, &00, &90, &21, &21, &00, &00
EQUB &0A, &A0, &52, &39, &00, &90, &21, &2D
EQUB &00, &00, &89, &A1, &65, &74
ELIF _SOURCE_DISK_CODE_FILES OR _SOURCE_DISK_ELT_FILES
EQUB &52, &00, &90, &20, &EA, &00, &00, &A7
EQUB &9F, &52, &61, &66, &74, &65, &72, &00
EQUB &90, &20, &F8, &00, &00, &B2, &9F, &52
EQUB &58, &32, &00, &90, &21, &04, &00, &00
EQUB &BD, &9F, &52, &58, &31, &00, &90, &21
EQUB &08, &00, &00, &C7, &9F, &52, &31, &00
EQUB &90, &21, &10, &00, &00, &D1, &9F, &52
EQUB &61, &00, &90, &21, &1B, &00, &00, &DB
EQUB &9F, &52, &36, &00, &90, &21, &34, &00
EQUB &00, &F2, &9F, &52, &34, &00, &90, &21
EQUB &36, &00, &00, &FC, &9F, &65, &74, &74
EQUB &65, &72, &00, &90, &21, &40, &00, &00
EQUB &0A, &A0, &52, &39, &00, &90, &21, &4C
EQUB &00, &00, &A1, &A1, &65, &74
ENDIF
ELSE
SKIPTO &C000
ENDIF
Right on, Commanders!
Mark Moxon