Author Topic: Another new loader and a request for artwork...  (Read 2220 times)

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Offline ralferoo

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Another new loader and a request for artwork...
« on: 19:44, 22 February 14 »
I'm in two minds as to whether to post this video or not, but I thought it might help me get some volunteers with my request if I do... :)

Turbo load v3 (emulator capture)

So, what's next... well I've been wanting to make a "tape based demo" for ages - and the fact this is the third version of my loader over about as many years probably indicates this... (in fact, it's funny that the source file is still called watch_tape.asm of which the original version was September 2011!) :)

This video shows loading 9x 16KB screens, so that's 144KB in 200 seconds... which makes this equivalent to 6272 baud. And it works fine using real tape too...  8)

Anyway, now that the tape loading is quick and reliable, I'm planning on making a tape demo hopefully in time for the Revision demoparty in April. I've got a few ideas of things I'd like to include, but it'd be really nice to showcase some CPC art as the audience at these parties are generally used to looking at C64 palettes. Some of the artwork that's possible on the CPC would really wow even the true C64 diehard fan!

One proviso is that these images must be previously unreleased work (required by demoparty rules) and whilst it'd be awesome to, for instance, use some of the recoloured loading screens on the thread here project news screens for old games , I'm a bit wary about doing that because I don't want to infringe on any copyrights on the original images. And again, as they're previously released work, it's not something I can really include anyway. (although I could maybe put them on at the end as a bonus feature!)

So, if you fancy contributing some images (and even better a slideshow sequence of image), that'd be fantastic! I've got some general advice about how to achieve the best results with this system, so if you're interested, contact me for more info!

I'd also like to add loading music too, but I can't use any of the standard players as everything needs to be very accurately cycle counted, but again if you've got some unreleased CPC music that might be perfect for this demo, let me know! Even if I can't use the player you use, I could maybe record the AY data using WinCPC and then make my own player from that... :)

If you're interested, let me know and I'll give you a rough idea of what I've got planned so far. But really, as I'm awful at art and music myself, I'd be happy to work the demo around most things!
« Last Edit: 19:52, 22 February 14 by ralferoo »

Offline Gryzor

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Re: Another new loader and a request for artwork...
« Reply #1 on: 19:51, 22 February 14 »
Fuck that's impressive... hope our artists do come forward :)

Offline mr_lou

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Re: Another new loader and a request for artwork...
« Reply #2 on: 20:00, 22 February 14 »
Very impressive indeed! I hope a graphics artist signs up!  :)

Offline robcfg

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Re: Another new loader and a request for artwork...
« Reply #3 on: 20:16, 22 February 14 »
Awesome!


And very nice selection of pictures! There should be more mode 1 games, hehe...  ;D

Offline ralferoo

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Re: Another new loader and a request for artwork...
« Reply #4 on: 20:24, 22 February 14 »
And very nice selection of pictures! There should be more mode 1 games, hehe...  ;D
The new pictures all came from http://genesis8.free.fr/archives/index.php?news_category=news_misc (06/27/2010) which eventually led me to http://genesis8.free.fr/frontend/graphic/pictgall.zip - there they're credited to Jill Lawson. EDIT: There's a CPCwiki page about her here: Jill Lawson - CPCWiki

But yeah, some version awesome mode 1 pixel art in there! :)

The first two images are the loading screen for Laser Squad and an in-game snapshot of Chimera, which I've been using as my default test images for years... but I finally got sick of them and wanted something nicer to look at! :)
 
« Last Edit: 20:33, 22 February 14 by ralferoo »

Offline TCMSLP

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Re: Another new loader and a request for artwork...
« Reply #5 on: 18:15, 07 March 14 »

That's some awesome work.  I have a soft spot for tape!
I haven't created tunes on the AY for a very long time but in the absence of any other offers, I'd certainly give it a go.

Steve / TCM

Offline McKlain

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Re: Another new loader and a request for artwork...
« Reply #6 on: 19:17, 07 March 14 »
if you need a tune, count me in  ;D

Offline pacomix

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Re: Another new loader and a request for artwork...
« Reply #7 on: 02:10, 09 March 14 »
This is amazing. You use also run length encoding in your loading routine plus some kind of error detection, right? How reliable is the loader routine regarding speed variations on a cassette?

Offline ralferoo

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Re: Another new loader and a request for artwork...
« Reply #8 on: 17:59, 09 March 14 »
This is amazing. You use also run length encoding in your loading routine plus some kind of error detection, right? How reliable is the loader routine regarding speed variations on a cassette?
It's better than RLE - it's closer to LZW encoding, but yeah it's realtime decompression direct into the load buffer... :)

The loader should be pretty reliable. My calculations suggest that ±20% of speed variation should be acceptable assuming perfect volume levels, although I'd say that in reality it's more likely to be closer to ±10%. When running in an emulator with perfect conditions, I was able to load from tape images running between 129% (super fast) and 76% (super slow) although these extremes can't be achieved with real tape. In my opinion, I think it should be more tolerant loading uncompressed data at around 2650 baud than standard loaders at 2000 baud, although I'll hold off with the details on that until after the demo when I'll release the source... :)

It's also a bleep loader, so the tape can be rewound to the bleep that occurs every second (that's actually just personal choice, each block specifies an address, length and 2-byte block number, so the bleep blocks can be as long as desired - initially I had 16KB blocks, but I'd see the occasional error (but actually, these seem to be always in the same place each time and I think it's a drop-out on the tape!) Each block has a CRC that's stronger than the Speccy style loaders, possibly less good than the CPC's system loader, but good enough in practice. Again this CRC is one that's in common use on modern computers, but again I'll say more when I release the source.
« Last Edit: 18:12, 09 March 14 by ralferoo »

Offline pacomix

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Re: Another new loader and a request for artwork...
« Reply #9 on: 13:47, 10 March 14 »
I'll say more when I release the source.


Great! So then would we be able to use freely this loader system? What is exactly the baud rate? 2650?

Offline ralferoo

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Re: Another new loader and a request for artwork...
« Reply #10 on: 15:02, 10 March 14 »
Great! So then would we be able to use freely this loader system? What is exactly the baud rate? 2650?
Yeah, that'd be totally fine! :)

The average baud rate is 2688 symbols per second. Unlike some other loaders, it's hard to increase that rate further though, but it was designed this way so I could make it multitask by having a fixed timing loop, and the primary motivation for that is so I can do background decompression to further increase throughput. Obviously, the gain from that depends a lot on the data, but it's essentially free and the compressor will never drop below the base bitrate.

Unlike most loaders, the actual data rate is a fixed speed - 336 characters per second. If you compare that to a 2000 baud turbo loader, that can reach 375 characters per second on all 0 bytes, but drops to 187 characters per second on all #ff bytes. Assuming random data, it's 250 characters per second from a normal turbo loader.