In the spotlight: The Tat/Avena Blog
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When looking at the Avena listings on Pouet or Demozoo one could be forgiven for thinking the crew is more or less inactive...
Register Allocation and the Cost Model
The m68k has 15 usable registers: d0-d7 and a0-a6 (a7 is the stack pointer, and sometimes a6 is also reserved as a frame pointer). For a CPU from 1979, this is actually quite generous; the 6502 has three, the Z80 and 8086 have seven or eight. So 15 should be plenty, right?
Not so fast. We have two register files with different capabilities. A pointer must be in an address register to dereference it. Most arithmetic must happen in data registers. For many use cases, we effectively have 7 or 8 registers to choose from, not 15. And if our function calls others, the ABI reserves the caller-clobbered registers, effectively leaving only ten registers: d3-d7/a2-a6 for free use with fastcall. When we run out, the allocator spills to the stack: on 68000, each 16-bit spill costs at least 16 cycles (8 to read, 8 to write back), and 32-bit values adds another 8. In a tight loop, it adds up fast.
When you write assembly, register allocation is intuition. You look at a routine and think: I need this value for the next three instructions, then I can reuse the register for something else. You juggle lifetimes in your head, naturally overlapping short-lived values. Teaching a computer this intuition is the fundamental challenge. The answer is to build a graph of which pseudo-registers are live simultaneously; two pseudos that overlap in lifetime interfere and cannot share a register. Then color the graph with K colors, one per available register, starting with the cheap caller-clobbered regs. When 19 pseudos from put_pixel compete for 15 registers, some will not fit — especially once you account for the data/address split — and those get spilled.
So how does GCC make the best of a difficult situation?
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- Written by: PeyloW
Read more: GCC for asm Experts (and C/C++ Intermediates) - Part 4
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Here are a few snapshots from Revision, provided by Lotek Style and Samurai. Thanks for sending those in!
Atarisceners spotted (from top left to down right): Havoc, Samurai, Havoc again (there can never be enough Havoc), NebulaH, Gunstick, Sgt Slayer (Atrocity!), JAC!, Lotek Style - not on the photo: Spiny and Havoc's friend with the sun glasses from last year ;p
A group photo may follow.
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- Written by: Lotek Style, Samurai & 505
The Outline Party 2026 will take place from May 14th to 17th! The freshly baked website is now available, so better get out your remote controls!
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- Written by: 505
Why is Atariscne.org reporting on a release of a new Amiga diskmag eh, CiH?
Well, yours truly offered to help out a friend, a little side-project, as it were.
‘Adventures in Retro’ is a long term project, created by a very good friend known as ‘Woodycool’ or Duncan, in civilian life. He’s a UK based retro-fan, primarily Amiga, but he also takes in a wide range of 8-bit interests, such as Commodore C16/Plus 4 and Amstrad CPC. He also owns and enjoys an Atari ST or two, so he’s living up to the ‘cool’ part of his nom-de-scene.
Anyway, I’ve been tempted to add a few articles, the sort of thing that wouldn’t fit easily in to atariscene.org. There is the future possibility that this mag could be released in other formats, including Atari.
If you have one of the other 16 bit machines, here’s a link to the home page, with a download of the first issue. - https://www.adv-in-retro.uk/ - It’s pretty compatible with most Amiga’s.
I do have an Amiga 600 waiting to be resurrected and slightly upgraded. I’ve been using the OSZX Online Amiga emulator in the meantime - OSZX Online Emulator
Anyway, enjoy!
CiH - Atariscne.org - April 2026.
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It's Easter time - and of course Revision party is taking place. A few Atari sceners will be present. Maybe we can share some impressions from the party later.
Here is an Atarian's management summary of the timetable:
Saturday
- 6 pm - compo block including oldschool music compo and ASCII compo
- 10 pm - compo block including Amiga intro, 256 byte and oldschool demo
Sunday
- 4 pm - compo block including oldschool graphics
- 6 pm - compo block with oldschool 4k intro and game compo
- 9:30 pm - compo marathon for the fittest, including Amiga demo compo
🔗 Official Revision time table
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- Written by: 505
The one and only Exocet has published an interesting résumé about his demoscene activities during the past 30 years on his blog 16 coleurs in French language.
In this summary you will find some interesting statistics, views, production examples and demo party photos.
"Vroum Paf" - a hidden gem, first place at Outline 2007, 16 colors
According to the visualized statistics Exocet had two major phases of activity, which might be typical for many sceners. One longer and rather normally distributed episode around the year 2000, when many graphics for demos like Odd stuff, many contributions to other groups like Alive team, YM-Rockerz, DHS, JFF, MJJ etc. were created. This period also originated many of the (bitter-)sweet character pictures in unique Exocet style.
Exocet's "Lapinots" - a classic and editor's all time favorite, among many!
And after a longer multi-year break around the year 2010 we witnessed a less excessive, but highly appreciated constant comeback on many different platforms until today.
"Enemy At The Gate Array" - winning picture at Shadow party 2025 oldschool graphics compo (Thomson T08 16 colors) - as Exocet puts it in the related text file, this one was "rushed with Grafx2 in a single day at the party place"
"Rate my ride" - That cat knows how to chose number plates.
🔗 30 years of demoscene on Exocet's blog "16 coleurs"
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Peter Kaczorowski published a tool for accessing and modifying Atari 8-Bit floppy disk images (ATR). This can be very handy for extracting, adding, updating or removing files from ATR images, directly via command line. The tool supports different kinds of Atari file systems and can be integrated in Midnight commander as well.
The functionality of atrfs reminds a bit to Krystone's extremely practical online disk image extractor for the bigger brother, the Atari ST with its ST/MSA-images. A similar browser based tool for visually investigate ATR images can be found here.
While the preference of a graphical or command line interface may be a matter of taste, the command line approach could turn out more sustainable regarding availability on the long term?
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- Written by: 505
The latest issue #69 of the long lasting Czech FLOP diskmag for Atari 8 Bit has been published.
Last year a pretaste of the mag art has been made available at Sillyventure and Last party. The mag itself was supposed to be released last year as well, but as life plays, the issue got delayed. As one feature, a Fujiama party report is said to be included. The diskmag comes as two ATR disk images.
🔗 Visit the FLOP website for download
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- Written by: 505
Richard Karsmakers aka Cronos of STNICCC party organisation fame has written a nostalgic reminiscence of the first steps of the Atari ST demoscene on his blog. The articled summarizes a brief initial time span about 40 years ago and is arguably a bit boldly, entitled "The Rise of the Atari ST Demo Scene".
A closer look at the blog generally indicates that Cronos, who was also one of the former ST News diskmag editors, still has an occasional inclination to write longer articles.
Speaking of STNICCC, the next party edition is about 6 years away. So get started with your entries! ;-)
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How GCC Actually Compiles
GCC originally stood for GNU C Compiler. Today it is the GNU Compiler Collection, with frontends for C, C++, Fortran, Ada, Go and more, a shared middle-end, and many backends. VAX and m68k were the first in 1987; today the list spans everything from modern x86-64 and ARM to legacy PDP-11 and MSP430. Each frontend parses its language and lowers it to a common intermediate representation. From there, the shared transformation passes take over, most of them entirely generic regardless of whether the target is a modern 64-core server or our humble 68000.
What happens between "C text goes in" and "assembly comes out" is roughly 360 of these passes, each rewriting the intermediate representation. Some optimize. Some check for errors. Some transform for consistency. Most do a little of everything. We will focus on the ones where our beloved 68000 needs the most help. I have put together a summary of all GCC passes for reference.
Debugging this pipeline is where the fun and the pain live. When the output is wrong, which of the 360 passes is at fault? Often it is not the obvious one; a bad decision in pass 47 might not surface as wrong, or inefficient, code until pass 180. Understanding the stages, even roughly, is the key to knowing where to look.
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- Written by: PeyloW
Read more: GCC for asm Experts (and C/C++ Intermediates) - Part 3
Here comes a little weekend starter kit. A production by a scener you may not haven't heard of, a release that is possibly widely overseen, for a platform many may not have heard of yet:
Kuvo of Caroline Software Incorporated released a new music disc for the Russian Elektronika BK-0010 computer (see wikipedia entry). And indeed, there is a scene for this one. And for a brief moment, the tiny Atariscene feels overdog! ;-)
Anyway, this music disk is quite a surprise, once you found it. It comes with one and a half hours of music for the twin brother of the YM2149F chip, the AY-3-8912. So Atari chipmusic stricken ears feel home immediately.
Very notably, KUVO did all of it, code, music and graphics. If you check his demozoo page you will stumble across an impressive backlog of fantastic ZX Spectrum graphics, too.
Among the tracks there are very enjoyable compositions in various styles, a good flow, sometimes laid back, sometimes uplifting and foremost nicely dynamic and catchy.
But there is more, actually, sound-wise this is way more advanced then the typical AY/YM bleepery. And a reason is found quickly, looking closely at the included VU-meters. The music disks supports 6 channels, so it is tailored for machines with two soundchips. And this offers some quality upgrade for the traditional AY soundscape, nice echoic detuned square leads, interesting slides plus reverb and delay for the masses!
Highly recommended!
🔗 Sight 4 draw by KUVO on Demozoo
🔗 Sight 4 draw by KUVO on Pouet
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- Written by: 505
The Atari ST Dev extension for Visual Studio Code is making progress.
Regis Cosnier (Dgis), the author summarizes the extension as follows:
"Atari ST Dev is a Visual Studio Code extension for building, running and debugging C, C++ and 68k assembly projects targeting Atari ST/TT/Falcon systems. It integrates a cross-toolchain using GCC/GDB, provides debug-time views for CPU registers, memory and hardware information, and hooks into Hatari's debugger via the cppdbg debug adapter."
🔗 Atari ST VS Code extension at Visual Studio Marketplace
🔗 Atari ST Visual Studio Code extension on Github
Thanks to flav_de for the hint!
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The Re-Falcon project has been put on display at last weekend's Indianapolis Retro Computer Expo 2026.
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The 10th edition of the Dutch Atari Meeting took place past weekend and judging by the photos available this was a great event for all Atari platforms.
According to wildly circulating rumours also some Atari sceners were present, some of them meeting as ripe men, decades after their previous encounter when they were fresh and young.
🔗 Photos on the respective Flickr homepage
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- Written by: 505
What a Compiler Must Get Right (That You Don't)
When you write assembly, you know the context. You know which registers hold what, whether a pointer is aligned, whether the loop count fits in a word. You know because you put it there.
Consider a demo screen where you reserve a6 for the background rasters. You update the pointer in the VBL interrupt and just advance with a minimal (a6)+ in the HBL. All your other code simply does not touch a6, because you wrote all of it. Need to update a screen pointer? Just write the global. No function call, no overhead, no uncertainty.
A compiler has no such luxury. It must be correct for every possible input the language allows. It cannot "just know" that a pointer is word-aligned, or that two buffers never overlap, or that a register is free. It must prove it, or assume the worst. And not all code it calls may even have been compiled by it. Maybe it was built with an older compiler, a different language, or maybe you wrote it in assembly yourself.
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- Written by: PeyloW
Read more: GCC for asm Experts (and C/C++ Intermediates) - Part 2
Some more old ‘new game’ news is heading our way.
This unexpected gift comes courtesy of Neil Rackett of Mesmotronic, who created the 3D model of an ST running in a browser window.
This time, he’s ported an ancient MS-DOS game ‘Sopwith’ to the ST.
It features intense biplane action through charmingly retro vector style graphics and arcade style gameplay, with characteristic MS-DOS beepy early PC sound. Interestingly, this game was going to get a dedicated ST version back in the day, but this did not happen, until now.
It can be downloaded from his Github repository. Good luck figuring out the controls!
CiH - 22.3.26.
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- Written by: CiH
This is a brain dump of what I have learned working with the GCC m68k backend, and maybe an attempt to convince someone else to try. This is the first of an unknown number of posts. No promises for how many there will be; I will continue as long as I have something to say and I find it fun.
I got my start with STOS Basic on an Atari 520STfm around 1990. Me and my classmate Tam formed T.O.Y.S. (Terror on Your ST) and I dubbed myself PeyloW. But in the scene, elite sceners wrote assembly; only lamers used STOS or GFA, every scroll text was clear about this. So we bought DevPac 2 and taught ourselves 68000 assembly, starting with snippets embedded in STOS and eventually graduating to full demo screens. The pattern that would follow me for decades was established early: high-level languages for tooling, assembly for anything that had to be fast. STOS gave way to PurePascal in the late '90s, but assembly remained the language that mattered — right through to the Falcon030 demo "Wait", released at EIL 2001.
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Read more: GCC for asm Experts (and C/C++ Intermediates) - Part 1
The live stream of this weekend's FOReVER party in Suchá nad Parnou, Slovakia can be found here. As it might be of relevance to understand what you see, this year's topic is "8bit winter games".
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Apparently, the Polish developer kTz from Retro Blitter Team known from his latest game Rogul is working on a STE enhanced version of Cannon Fodder, to finally catch up with the Am***.
The friends of the Polish Atariarea portal prepared this nice preview video
Atarimania also lists a WIP version already.
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- Written by: Lotek Style & 505
gwEm writes:
In order to encourage people to enter the Buxton Bytes sample demo showcase I am releasing the full source code to my entry way in advance of the event.
https://github.com/gwEm303/sample_demo
The demo will run on a 1MB STe from a 11 sector 82 track DSDD disk. It incorporates the Kalms ADPCM route, a sample sequencer and three alternative memory management schemes.
As an example, a version of Daft Punk's "One More Time" in mono with a hybrid 25/12kHz sample rate.
I attach an MSA file those who are not keen to assemble the source code may try.
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- Written by: gwEm
