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Nice to meet you Zuffle. Always great to meet new folks interested in potential collaborations on retro productions! Would love to hear some new music for the Beeb's lowly SN76489 chip. What Tracker do you use these days?

Quick update that the build process now creates an unencrypted / non-checksum'd version of the loader and game by default, so won't be binary identical. Added a new build target 'encrypt' and changed the verify batch file to make encrypted versions again to compare against the originals. I've starte...

Use COPYBLOCK start, end, destination to assemble code at the correct location and then copy it to a different location for loading. Gets around the lack of O%.

If I had mutable variables then I'd be able to implement the Elite checksum calculation code directly in the BeebAsm source (ala the BBC BASIC assembler) without having to resort to Python. I've just realised I can likely abuse the COPYBLOCK command to poke individual byte values back into the outpu...

Thanks Kevin. Yes, the code being 'terse' is an understatement. It helps a bit with the whitespace and one statement per line but it's still tough to follow without any meaningful labels. I will see about tracing through the code a little way to at least comment the functions in the main loop.

Today I hacked the Elite loader. Probably been done many times before but was easier with the source to hand..!

A small update: I've commented the loader source so I can remove the checksums / encryption / tamper protection. For those interested, this is what the Elite loader does - some sneaky stuff in here! \ ENTRY code at &20C9 \ Disable all interupts \ Set USERV, BRKV, IRQ2V and EVENTV to point to machine...

Quick update, I've improved the whitespace so assembler instructions are legible and all labels are on their own line. If anyone feels like identifying and renaming labels to something more meaningful then please feel free.

I thought it had been too long since I gave you any presents so here is an initial port of the BBC Elite source code from BBC BASIC to BeebAsm. It can be built on a modern PC development environment to produce binary identical exexcutables. Everything is in GitHub here: https://github.com/kieranhj/e...

Reverse emulating the NES: https://www.youtube.com/watch?v=ar9WRwCiSr0

Very reminiscent of Pi-CoPro but for the NES - a remarkable achievement!

Extra making of here: https://www.youtube.com/watch?v=hTlNVUmBA28

A real 'B' give the correct image as do the two Masters that I have tried using MMC, but the two Masters that I have tried with data centres give the image on the left, but I'm not sure how far off the timing is. Could it be the type of 6845 that's causing the issue? For reference, mine is a Hitach...

Minor comment, but could you fix the downloadable SSD to conform to DFS. It's missing the sector count at offset &106-&107. A Watford DFS reports 00 tracks, and MAME requires this to determine the format of the file whether 40/80 tracks. For 40 tracks replace bytes &106-&107 with &31, &90. For 80 t...

Hey Tricky & Steve, thanks for the kind words. I think I've got a few credits in hand on the "why can't they put that effort into a game" front, so I'm happy to spend some on a demo. ;) Thanks for providing your vsync code, I will definitely take a look. NOP slides are fun and I will probably revisi...

Thanks for the kind words everyone - will write a longer reply when I get chance. For now just pinging the subcribers that we're up to part #10!

Please do feel free to ask clarifying questions.

6502 newbie here so perhaps this is obvious to everyone else... But can I ask why there are 9 nops but the comments say they take 16 cycles? Wouldn't it be 18? It's 18; the comment is wrong. As to *why* it's 18: much of this code was written empirically. The way I got it working is to make a loop t...

I wrote this code! Original post is here: http://www.retrosoftware.co.uk/forum/viewtopic.php?f=73&t=1007 . (And this demo is just the kind of thing I was hoping people would use it, or the principles behind it, for. Keep up the good work!) Edit: wait, I am confused. You linked to this post further ...

Not sure if edits get flagged in thread subscriptions so just noting that I've added notes for the Copper Colours and Plasma effects! More soon.

I received some nice PM's from people enjoying this technical thread but not wanting to mess up the flow of the articles. At the risk of slightly making a rod for my own back, I've added placeholder posts for the remaining topics I wanted to cover (i.e. everything) so that discussion may continue be...

Part 15: Miscellaneous Debris Memory usage [/u] Here are some memory stats from the assembler output: ------ INFO (MAIN RAM) ------ MAIN size = &1C5 VGM PLAYER size = &B4 EXOMISER size = &134 DISKSYS size = &8E PUCRUNCH size = &18C SWR size = &6 PRINT size = &14 SCRIPT size = &146 ------ HELPERS si...

Part #14: Smiley Drop Towards the end of the project, I asked Dethmunk if he was inspired to draw any more artwork for the demo and he replied with the Smiley picture as he said this was a trippy acid demo! I've been wanting to mess around with the smooth (single scanline) vertical scrolling techni...

Part #13: Twister I've saved the Twister to (near) the end as it's probably the most technically complex effect using 40K of prerendered single scanline screen buffers. But, given everything we've learnt about the CRTC by now, should be relatively easy to explain. The Twister is an iconic demoscene...

Part #12: Bitshifters "MODE 7" logo You've probably guessed by now that the wibbling Bitshifters logo at the start of the demo isn't MODE 7 at all but MODE 1. :) I took a screen grab of Steve Horsley's original Acornsoft x Bitshifters Teletext logo that he made for Prince of Persia and passed it th...

Part #11: Checkerboard Zoom The zooming checkerboard turned out to require more iterations than originally anticipated (for reasons that I will get onto shortly) and actually does the most work in the update function (during vblank) of all the effects. As with the Kefrens bars, the CRTC configurati...

Part #10: Kefrens aka Alcatraz bars I have been on a quest to produce true single scanline Kefrens bars on the Beeb for quite a while. Here's a very early protoype of the effect from 2016 which is only achieving one bar every 8 scanlines for a massive total of 28x bars! kefrens bars circa 2016.png ...

Part #9: Vertical Blinds The "Vertical Blinds" effect was one of the earliest that I prototyped whilst experimenting with vertical rupture to repeat a single character row over the entire screen for "free". The original code used IRQV1 callbacks before the FX framework existed. I wasn't going to in...

Part #8: Parallax Bars The entirety of Twisted Brain was pretty much based on my desire to recreate the Parallax Bars and other effects from one of my all-time favourite demos of the Amiga era: Total Triple Trouble by Rebels . It follows the same 64 x 1 x 4 CRTC cycle configuration as both the Copp...

Part #7: Plasma Like the Copper Colours, the Plasma effect is also in MODE 0 and uses a prerendered screen buffer consisting of various 4x4 ordered dither patterns: plasma prerendered screen.png Although this looks a bit random, every two character rows consists of a gradient that goes from white -...

Part #6: Copper Colours Hopefully now we have enough knowledge of the CRTC registers and vertical rupture technique to be able to explain how the copper colour effect was achieved. But first we need a small diversion on dithering . We know the BBC colour palette is limited to 3-bit RGB so eight int...

Part 5: Vertical Rupture Vertical Rupture is the term coined by the CPC community for the technique of programming the CRTC so that it goes through more than one display cycle per PAL frame. This is a very powerful technique that allows us to effectively map the screen buffer to the screen display ...

Part #4: A brief introduction to CRTC registers Before explaining any more about the effects in the demo, it is worth briefly covering the CRTC registers. Reference this table in p190 of the NAUG: CRTC registers.PNG As noted before, there is no difference between MODES 0,1,2 as far as the CRTC is c...