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Mark Moxon

@markmoxon.bsky.social

Writer, walker, software archaeologist. Back in the day: Editor of Acorn User, Editor of h2g2. I love analysing old code, and my aim is to create the best code disassemblies you have ever seen. Purveyor of Elite/Lander/Revs hacks. www.markmoxon.com

969 Followers  |  337 Following  |  594 Posts  |  Joined: 11.12.2023  |  2.0219

Latest posts by markmoxon.bsky.social on Bluesky

Good point. And it is easy to understand, that's for sure. The biggest confusion is when codebases mix sign-magnitude and signed numbers... but who would do that?

Well, apart from Bell and Braben, obviously. πŸ˜†

10.02.2026 14:19 β€” πŸ‘ 1    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

Oof, Elite's sign-magnitude numbers are a bit of an acquired taste - I'm not sure whether I'd perpetuate that particular design decision! Multi-byte signed numbers might be easier to handle if you're after a bigger model space, though both solutions do work, so I guess it's down to personal taste!

10.02.2026 14:07 β€” πŸ‘ 1    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

Well, that looks pretty great! Nice to see it all working live. πŸ‘

10.02.2026 13:37 β€” πŸ‘ 1    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

Yeah, it might take a while... but there's a lot to say. πŸ˜€

31.01.2026 16:17 β€” πŸ‘ 0    πŸ” 0    πŸ’¬ 0    πŸ“Œ 1
The list of deep dives that I am working on

The list of deep dives that I am working on

I've started writing a series of deep dives into Geoff Crammond's epic #BBCMicro game The Sentinel.

Here's the to-do list.

I will post a link here whenever I add a new one to thesentinel.bbcelite.com

It's going to take a while! But it should be worth it...

#retrocomputing #retrogaming #c64 #8bit

31.01.2026 15:56 β€” πŸ‘ 48    πŸ” 5    πŸ’¬ 4    πŸ“Œ 0
The Sentinel in embroidery

The Sentinel in embroidery

You didn't know you needed this in your life, but you do.

Marine Beaufils is a French artist who creates beautiful embroideries of... The Sentinel (amongst others).

It's inspired and quite beautiful. Enjoy!

www.marine.st/en/pages/sen...

#bbcmicro #zxspectrum #c64 #retrogaming #retrocomputing

13.01.2026 11:42 β€” πŸ‘ 29    πŸ” 4    πŸ’¬ 2    πŸ“Œ 0

Glad you like it - that full view is quite something!

12.01.2026 12:01 β€” πŸ‘ 1    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0

Oh yeah, I see what you mean. Interesting, I guess that must be a typo in the MAME comment, because the ARM5 definitely isn’t a thing.

It’s nothing to do with the subject of your blog post, though, so I’ll shut up and go back to reading the good stuff. 🫑

11.01.2026 21:25 β€” πŸ‘ 1    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0

Totally agree.

11.01.2026 21:02 β€” πŸ‘ 1    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0
List of ARM processors - Wikipedia

Great article! You’re one of the few bloggers whose stuff I always read, no regrets.

One thing: β€œthe DECO 156 was apparently a custom encrypted ARM5 CPU”.

I don’t think there’s such a thing as an ARM5? Could it be ARM3, ARM6 or possibly ARM7, given the timeline?

en.wikipedia.org/wiki/List_of...

11.01.2026 20:59 β€” πŸ‘ 2    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

Take away the slow panning and the tiny POV and it isn't really the same game. The faster versions are OK, as the strategy of the game is still great, but I do feel they miss out on the magic of the original.

Sometimes faster gameplay and bigger POVs aren’t better - they’re just different, I guess!

11.01.2026 20:42 β€” πŸ‘ 2    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

It would be a different game, I suspect! The genius of the original is in the claustophobia of the small POV and the feeling of being trapped.

You know those dreams where you're desperate to run away but your feet are stuck to the floor?

That's the original version of The Sentinel.

11.01.2026 20:42 β€” πŸ‘ 0    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0
Preview
Atomic Elite Hi guys, I want to share information about my latest conversion project for the Acorn Atom: ........ Atomic Elite. The source files are taking from the

And here’s the thread on Stardot about it. It’s been around for a while now!

stardot.org.uk/forums/viewt...

11.01.2026 19:22 β€” πŸ‘ 0    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0
Preview
GitHub - oss003/Elite: An Acorn Electron conversion of Elite for the Acorn Atom An Acorn Electron conversion of Elite for the Acorn Atom - oss003/Elite

It’s already been done! Atomic Elite is a real thing. πŸ˜€

I don’t know a lot about the Atom so I’m not sure if it needs an upgraded machine, but it definitely exists.

github.com/oss003/Elite

11.01.2026 19:20 β€” πŸ‘ 1    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

The modern remakes, though? I bet they could do it no problem!

11.01.2026 18:23 β€” πŸ‘ 0    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

Also, the game uses the equirectangular projection, and that won’t change, so all you’d get would be more of the existing view squished into each screen, rather than the perspective shift in Minecraft.

Not sure Quake Pro real is a concept within the equirectangular world, outside of zooming… πŸ€”

11.01.2026 18:21 β€” πŸ‘ 1    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

Ah, OK found it - in Minecraft, WTF!

Yes, I think it would be possible to squeeze more angles into a single screen view, but the Beeb just doesn’t have the resolution for this to look good, and it would require a fair amount of recoding.

So that’s probably a technical β€œyes”only!

11.01.2026 18:16 β€” πŸ‘ 0    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

What’s Quake Pro field of view?

11.01.2026 17:56 β€” πŸ‘ 0    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

I might do a proper one-to-one at some point, but this took ages - loads of individual screenshots, each one cropped from the b2 export and then stitched together (the starting screen image in this thread is an example of a b2 export).

I wrote an ImageMagick script, but still, it took forever!

11.01.2026 17:22 β€” πŸ‘ 2    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0

Also, they don’t match mode 5 pixels anyway, as they are rectangular, so that’s another mismatch!

They’re just a bit of fun, not exact matches - I probably should have been explicit in saying this, but things always get missed out in these tiny messages!

11.01.2026 17:11 β€” πŸ‘ 1    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

That’s because I exported these from the b2 emulator, which applies a horizontal correction that can’t be disabled (that’s the aliasing you’re seeing).

I didn’t say these were one-to-one pixel screenshots directly from the BBC screen, as they aren’t. They just show the full landscape in one go.

11.01.2026 17:11 β€” πŸ‘ 1    πŸ” 0    πŸ’¬ 2    πŸ“Œ 0

All three of which were born on the BBC Micro. πŸ˜€

You have good taste!

10.01.2026 17:59 β€” πŸ‘ 3    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

Well put! This game is a work of art and so atmospheric.

Scary too. And eerie at times. It’s so clever…

10.01.2026 17:42 β€” πŸ‘ 2    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0
The initial screen in The Sentinel

The initial screen in The Sentinel

And here's the game's opening screen, for reference.

10.01.2026 17:20 β€” πŸ‘ 7    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0

To see the landscape images in their full glory (i.e. without social media trying to be helpful), here are links to the full images:

Plain landscape: thesentinel.bbcelite.com/images/panor...

Landscape with grid points: thesentinel.bbcelite.com/images/panor...

Zoom in to see the detail...

10.01.2026 17:12 β€” πŸ‘ 4    πŸ” 0    πŸ’¬ 2    πŸ“Œ 0
Preview
Fully documented source code for The Sentinel on the BBC Micro Fully documented source code disassembly for The Sentinel on the BBC Micro, with lots of deep dive articles explaining how every aspect of the game works.

For those who don't know, The Sentinel is a classic game from 1986, written by Geoff Crammond and published by Firebird.

It was originally released on the BBC Micro, and was converted to lots of other home computers, including the Commodore 64, ZX Spectrum.

See thesentinel.bbcelite.com for more.

10.01.2026 17:10 β€” πŸ‘ 5    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

So the game screen shows shows 1/9.7 of the full height and 1/12.8 of the full width of the landscape.

The weird figures are because the screen is a different shape to the full view.

Also visible is the point carΓ©e equirectangular projection used in the game. This is taken straight from Revs.

10.01.2026 17:10 β€” πŸ‘ 3    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0
The first level in The Sentinel

The first level in The Sentinel

The first level in The Sentinel showing grid points for panning and the first screen in red

The first level in The Sentinel showing grid points for panning and the first screen in red

Have you ever wondered how big the full landscape is in The Sentinel?

It's 1856 pixels high and 2048 pixels wide.

Here's the first level. The initial 192x160 screen is in red. Panning jumps the view to different grid points.

It's a big old world!

#retrocomputing #retrogaming #bbcmicro #c64 #8bit

10.01.2026 17:10 β€” πŸ‘ 48    πŸ” 8    πŸ’¬ 3    πŸ“Œ 1

Yes, you can look up a surprisingly long way, though in the early levels things are relatively flat so all you see is screen after screen of sky. When you look down you can see your own tile, so that’s a bit easier to fathom.

I’ve been making panorama shots, so I might make a post on this topic!

10.01.2026 11:25 β€” πŸ‘ 1    πŸ” 0    πŸ’¬ 0    πŸ“Œ 0

In mode 5 pixels, the full landscape view is 1856 pixels high and 2048 pixels wide.

The game screen shows shows 192 by 160 pixels, so that's 1/9.7 of the full height and 1/12.8 of the full width.

The weird figures are because the screen is a different shape to the full view.

There you go!

(2/2)

09.01.2026 23:19 β€” πŸ‘ 4    πŸ” 0    πŸ’¬ 1    πŸ“Œ 0

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