BBC Micro (cassette) | BBC Micro (disc) | 6502 Second Processor | BBC Master | Acorn Electron | Elite-A | NES
This repository contains source code for the disc version of Elite on the BBC Micro, with every single line documented and (for the most part) explained.
It is a companion to the bbcelite.com website.
See the introduction for more information.
This repository contains source code for the disc version of Elite on the BBC Micro, with every single line documented and (for the most part) explained.
You can build the fully functioning game from this source. Two variants are currently supported: the version from Ian Bell's personal website, and the version from the Stairway to Hell archive.
It is a companion to the 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.
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If you want to browse the source and read about how Elite works under the hood, you will probably find the website is a better place to start than this repository.
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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.
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If you want to build Elite from the source on a modern computer, to produce a working game disc that can be loaded into a BBC Micro or an emulator, then you want the section on Building 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.
Elite was written by Ian Bell and David Braben and is copyright © Acornsoft 1984.
The code on this site has been reconstructed from a disassembly of the version released on Ian Bell's personal website.
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; to Paul Brink for his annotated disassembly; and to Kieran Connell for his BeebAsm version, which I forked as the original basis for this project. You can find more information about this project in the accompanying website's project page.
Thanks to the Bitshifters for their help in building the musical version of BBC Micro Elite, and in particular Kieran Connell, Simon Morris and Negative Charge for the music player and ported music files. Thanks also to Tricky and J.G.Harston for their sideways RAM utilities.
The following archive from Ian Bell's personal website forms 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:
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The main game's source code is in the elite-source-flight.asm and elite-source-docked.asm files (for when we're in-flight or docked) - this is the motherlode and probably contains all the stuff you're interested in.
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The game's loader is in the elite-loader1.asm, elite-loader2.asm and elite-loader3.asm files - these are mainly concerned with setup and copy protection.
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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
TT170, which you can find by searching forName: TT170. 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 BBC 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-discs contains the final output of the build process: an SSD disc image that contains the compiled game and which can be run on real hardware or in an emulator.
This repository also includes a flicker-free version, which incorporates the backported flicker-free ship-drawing routines from the BBC Master, as well as a fix for planets so they no longer flicker. The flicker-free code is in a separate branch called flicker-free, and apart from the code differences for reducing flicker, this branch is identical to the main branch and the same build process applies.
The annotated source files in the flicker-free branch contain both the original Acornsoft code and all of the modifications for flicker-free Elite, so you can look through the source to see exactly what's changed. Any code that I've removed from the original version is commented out in the source files, so when they are assembled they produce the flicker-free binaries, while still containing details of all the modifications. You can find all the diffs by searching the sources for Mod:.
The repository also includes a variant that incorporates both the flicker-free ship-drawing routines and a fix for planets so they no longer flicker, though this version only works when running on a BBC Master. The flicker-free code is in a separate branch called bbc-master-flicker-free.
For more information on flicker-free Elite, see the hacks section of the accompanying website.
This repository also includes a version of BBC Micro Elite that includes the music from the Commodore 64 version. The music-specific code is in a separate branch called music, and apart from the code differences for adding the music, this branch is identical to the main branch and the same build process applies.
The annotated source files in the music branch contain both the original Acornsoft code and all of the modifications for the musical version of Elite, so you can look through the source to see exactly what's changed. Any code that I've removed from the original version is commented out in the source files, so when they are assembled they produce the music-enabled binaries, while still containing details of all the modifications. You can find all the diffs by searching the sources for Mod:.
The music itself is built as a sideways ROM using the code in the elite-music repository.
For more information on the music, see the hacks section of the accompanying website.
This repository also includes a version of BBC Micro disc Elite that will run on a BBC Master (unlike the original, which crashes when loaded into a Master). The BBC Master version is in a separate branch called bbc-master, and apart from the code differences for supporting the Master, this branch is identical to the main branch and the same build process applies.
The annotated source files in the bbc-master branch contain both the original Acornsoft code and all of the modifications required to make BBC Micro Elite run on the Master, so you can look through the source to see exactly what's changed. Any code that I've removed from the original version is commented out in the source files, so when they are assembled they produce the Master-compatible binaries, while still containing details of all the modifications. You can find all the diffs by searching the sources for Mod:.
The repository also includes a variant of the BBC Master version that incorporates both the flicker-free ship-drawing routines and a fix for planets so they no longer flicker. The flicker-free code is in a separate branch called bbc-master-flicker-free.
For more information on the port to the BBC Master, see the hacks section of the accompanying website.
You will need the following to build 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. Both versions 2.7 and 3.x should work.
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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).
For details of how the build process works, see the build documentation on bbcelite.com.
Let's look at how to build Elite from the source.
There are two main build targets available. They are:
build- An unencrypted versionencrypt- An encrypted version that includes the same obfuscation as the released version of the game
The unencrypted version should be more useful for anyone who wants to make modifications to the game code. It includes a default commander with lots of cash and equipment, which makes it easier to test the game. As this target produces unencrypted files, the binaries produced will be quite different to the binaries on the original source disc, which are encrypted.
The encrypted version contains an obfuscated version of the game binary, along with the standard default commander.
Builds are supported for both Windows and Mac/Linux systems. In all cases the build process is defined in the Makefile provided.
For Windows users, there is a batch file called make.bat to which you can pass one of the build targets above. Before this will work, you should edit the batch file and change the values of the BEEBASM and PYTHON variables to point to the locations of your beebasm.exe and python.exe executables. You also need to change directory to the repository folder (i.e. the same folder as make.bat).
All being well, doing one of the following:
make.bat build
make.bat encrypt
will produce a file called elite-disc-sth.ssd in the 5-compiled-game-discs folder that contains the Stairway to Hell variant, which you can then load into an emulator, or into a real BBC Micro using a device like a Gotek.
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 or Python are not on your path, then you can either fix this, or you can edit the Makefile and change the BEEBASM and PYTHON variables in the first two 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, doing one of the following:
make build
make encrypt
will produce a file called elite-disc-sth.ssd in the 5-compiled-game-discs folder that contains the Stairway to Hell variant, which you can then load into an emulator, or into a real BBC Micro using a device like a Gotek.
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 build process also supports a verification target that prints out checksums of all the generated files, along with the checksums of the files from the original sources.
You can run this verification step on its own, or you can run it once a build has finished. To run it on its own, use the following command on Windows:
make.bat verify
or on Mac/Linux:
make verify
To run a build and then verify the results, you can add two targets, like this on Windows:
make.bat encrypt verify
or this on Mac/Linux:
make encrypt verify
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 encrypt verify, then this is the output of the verification process:
Results for variant: sth
[--originals--] [---output----]
Checksum Size Checksum Size Match Filename
-----------------------------------------------------------
a9ee9d74 17437 a9ee9d74 17437 Yes D.CODE.bin
dad7d3a3 17437 dad7d3a3 17437 Yes D.CODE.unprot.bin
9f4a04fd 2560 9f4a04fd 2560 Yes D.MOA.bin
d9eb34f9 2560 d9eb34f9 2560 Yes D.MOB.bin
93fe2e13 2560 93fe2e13 2560 Yes D.MOC.bin
64e8ebb4 2560 64e8ebb4 2560 Yes D.MOD.bin
80afbff9 2560 80afbff9 2560 Yes D.MOE.bin
b86fe100 2560 b86fe100 2560 Yes D.MOF.bin
72f99614 2560 72f99614 2560 Yes D.MOG.bin
29b6ce81 2560 29b6ce81 2560 Yes D.MOH.bin
0eeab415 2560 0eeab415 2560 Yes D.MOI.bin
7911181d 2560 7911181d 2560 Yes D.MOJ.bin
851d789f 2560 851d789f 2560 Yes D.MOK.bin
3025e5d8 2560 3025e5d8 2560 Yes D.MOL.bin
d6c01098 2560 d6c01098 2560 Yes D.MOM.bin
6930e1c7 2560 6930e1c7 2560 Yes D.MON.bin
43caddc7 2560 43caddc7 2560 Yes D.MOO.bin
ac1d57b2 2560 ac1d57b2 2560 Yes D.MOP.bin
c73d535a 256 c73d535a 256 Yes ELITE2.bin
17eefeec 2816 17eefeec 2816 Yes ELITE3.bin
ec04b4d2 5376 ec04b4d2 5376 Yes ELITE4.bin
10417c14 5376 10417c14 5376 Yes ELITE4.unprot.bin
0f9e270b 256 0f9e270b 256 Yes MISSILE.bin
42f42f63 19997 42f42f63 19997 Yes T.CODE.bin
8819c78b 19997 8819c78b 19997 Yes T.CODE.unprot.bin
52bac547 1024 52bac547 1024 Yes WORDS.bin
All the compiled binaries match the originals, so we know we are producing the same final game as the Stairway to Hell 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).
For users of the excellent b2 emulator, you can include the build parameter b2 to automatically load and boot the assembled disc image in b2. The b2 emulator must be running for this to work.
For example, to build, verify and load into b2, you can do this on Windows:
make.bat encrypt verify b2
or this on Mac/Linux:
make encrypt verify b2
Note that you should manually choose the correct platform in b2 (I intentionally haven't automated this part to make it easier to test across multiple platforms).
This repository contains the source code for two different variants of the disc version of Elite:
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The variant from the Stairway to Hell archive
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The variant from the game disc on Ian Bell's website
By default the build process builds the Stairway to Hell variant, but you can build a specified variant using the variant= build parameter.
You can add variant=sth to produce the elite-disc-sth.ssd file containing the Stairway to Hell variant, though that's the default value so it isn't necessary.
The verification checksums for this version are as follows:
Results for variant: sth
[--originals--] [---output----]
Checksum Size Checksum Size Match Filename
-----------------------------------------------------------
a9ee9d74 17437 a9ee9d74 17437 Yes D.CODE.bin
dad7d3a3 17437 dad7d3a3 17437 Yes D.CODE.unprot.bin
9f4a04fd 2560 9f4a04fd 2560 Yes D.MOA.bin
d9eb34f9 2560 d9eb34f9 2560 Yes D.MOB.bin
93fe2e13 2560 93fe2e13 2560 Yes D.MOC.bin
64e8ebb4 2560 64e8ebb4 2560 Yes D.MOD.bin
80afbff9 2560 80afbff9 2560 Yes D.MOE.bin
b86fe100 2560 b86fe100 2560 Yes D.MOF.bin
72f99614 2560 72f99614 2560 Yes D.MOG.bin
29b6ce81 2560 29b6ce81 2560 Yes D.MOH.bin
0eeab415 2560 0eeab415 2560 Yes D.MOI.bin
7911181d 2560 7911181d 2560 Yes D.MOJ.bin
851d789f 2560 851d789f 2560 Yes D.MOK.bin
3025e5d8 2560 3025e5d8 2560 Yes D.MOL.bin
d6c01098 2560 d6c01098 2560 Yes D.MOM.bin
6930e1c7 2560 6930e1c7 2560 Yes D.MON.bin
43caddc7 2560 43caddc7 2560 Yes D.MOO.bin
ac1d57b2 2560 ac1d57b2 2560 Yes D.MOP.bin
c73d535a 256 c73d535a 256 Yes ELITE2.bin
17eefeec 2816 17eefeec 2816 Yes ELITE3.bin
ec04b4d2 5376 ec04b4d2 5376 Yes ELITE4.bin
10417c14 5376 10417c14 5376 Yes ELITE4.unprot.bin
0f9e270b 256 0f9e270b 256 Yes MISSILE.bin
42f42f63 19997 42f42f63 19997 Yes T.CODE.bin
8819c78b 19997 8819c78b 19997 Yes T.CODE.unprot.bin
52bac547 1024 52bac547 1024 Yes WORDS.bin
You can build the Ian Bell disc variant by appending variant=ib-disc to the make command, like this on Windows:
make.bat encrypt verify variant=ib-disc
or this on a Mac or Linux:
make encrypt verify variant=ib-disc
This will produce a file called elite-disc-ib-disc.ssd in the 5-compiled-game-discs folder that contains the Ian Bell disc variant.
The verification checksums for this version are as follows:
Results for variant: ib-disc
[--originals--] [---output----]
Checksum Size Checksum Size Match Filename
-----------------------------------------------------------
7b8eceb7 1418 - - - !BOOT.bin
25be225d 17437 25be225d 17437 Yes D.CODE.bin
56876c8a 17437 56876c8a 17437 Yes D.CODE.unprot.bin
9f4a04fd 2560 9f4a04fd 2560 Yes D.MOA.bin
d9eb34f9 2560 d9eb34f9 2560 Yes D.MOB.bin
93fe2e13 2560 93fe2e13 2560 Yes D.MOC.bin
64e8ebb4 2560 64e8ebb4 2560 Yes D.MOD.bin
80afbff9 2560 80afbff9 2560 Yes D.MOE.bin
b86fe100 2560 b86fe100 2560 Yes D.MOF.bin
72f99614 2560 72f99614 2560 Yes D.MOG.bin
29b6ce81 2560 29b6ce81 2560 Yes D.MOH.bin
0eeab415 2560 0eeab415 2560 Yes D.MOI.bin
7911181d 2560 7911181d 2560 Yes D.MOJ.bin
851d789f 2560 851d789f 2560 Yes D.MOK.bin
3025e5d8 2560 3025e5d8 2560 Yes D.MOL.bin
d6c01098 2560 d6c01098 2560 Yes D.MOM.bin
6930e1c7 2560 6930e1c7 2560 Yes D.MON.bin
43caddc7 2560 43caddc7 2560 Yes D.MOO.bin
ac1d57b2 2560 ac1d57b2 2560 Yes D.MOP.bin
86e4a1ef 256 c73d535a 256 No ELITE2.bin
fd788d2a 2304 17eefeec 2816 No ELITE3.bin
7abce0df 5376 74278df9 5376 No ELITE4.bin
10417c14 5376 8862453f 5376 No ELITE4.unprot.bin
e51c9eae 256 - - - ELITE5.bin
e99072dc 256 - - - ELITE6.bin
0f9e270b 256 0f9e270b 256 Yes MISSILE.bin
6b22a971 19997 6b22a971 19997 Yes T.CODE.bin
a1cf4199 19997 a1cf4199 19997 Yes T.CODE.unprot.bin
52bac547 1024 52bac547 1024 Yes WORDS.bin
The failed matches are because I haven't yet converted the loader into BeebAsm source files (see the next section for details).
You can see the differences between the variants by searching the source code for _STH_DISC (for features in the Stairway to Hell variant) or _IB_DISC (for features in the Ian Bell game disc variant). There are only a few differences:
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The Ian Bell variant contains the refund bug, which has been fixed in the Stairway to Hell variant
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The Ian Bell variant never spawns asteroids, which has been fixed in the Stairway to Hell variant
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The Ian Bell variant sets bit 2 of the competition flag in the commander file, while the Stairway to Hell variant sets bit 5
In other words, the Ian Bell variant appears to be the very first release of the disc version of Elite, while the Stairway to Hell variant has both bugs fixed and a bumped-up number in the competition flag.
See the accompanying website for a comprehensive list of differences between the variants.
Note that I have only included differences that appear in the main game code, rather than those that appear in the loaders, as these files can differ extensively between variants without affecting the game itself. The variant on Ian Bell's personal website contains a whole load of copy protection differences when compared to the same code in the Stairway to Hell variant, and it also contains two more binary files (ELITE5 and ELITE6), plus a !BOOT file that contains even more copy protection code. I haven't disassembled the loader files from this variant as that's a whole different rabbit hole, so if you build the Ian Bell variant with make encrypt verify, the compiled loader binaries will not match those extracted from the original disc. The main binaries will match, however, which is the interesting part from a digital archaeology perspective, as that's where the bug fixes live.
Right on, Commanders!
Mark Moxon