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Atari Beaglebone Expansion

Xuel

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Ilmenit's RastaConverter is an image conversion tool for Atari 8-bit computers. I wrote RastaMovie to stitch RastaConverter images together to make movies. The movie frames have to be switched very quickly to achieve a frame rate of 25-30 frames per second. This rules out SIO or IDE interfaces as you need around 500 KB/s throughput. You have to have the frames in memory. But the largest memory expansion commonly available is only 1088K. That's only enough for around 64 frames and they have to be cut down to 16K a piece from their normal size of around 22K so they don't fill the screen.

 

Thus, the genesis of the Atari Beaglebone Expansion or ABX. Integrating the Atari with a Beaglebone as a PBI device, I was able to effectively expand available memory to 140MB on a stock Atari 600XL. This is enough to play around 3.5 minutes of video at 30 FPS.

 

But, what's a movie without sound? So, I modified RastaConverter to reserve room on each scan line of the raster program to write a digital sample to POKEY and then to restore the register that had to be modified in order to do that. Then I positioned additional writes to POKEY in the intra-frame kernel so that the audio plays uninterrupted.

 

You can see the result in this YouTube video:

 

http://www.youtube.com/watch?v=1irR4TQ5aMA

 

RastaMovie can also output versions of the movies that can be played on Atari800 and Altirra. It takes advantage of the fact that segment loads are instantaneous to simulate large amounts of RAM. These executables won't work on real hardware however. Check out birds.zip, epic.zip and im.zip in the downloads area of RastaMovie's github home page.

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I wonder if this movie player and movies can be converted to AVG use... or if the beaglebone expansion would be updated/moved to more solutions encompassing all of these other upgrades these days

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1 hour ago, _The Doctor__ said:

I wonder if this movie player and movies can be converted to AVG use... or if the beaglebone expansion would be updated/moved to more solutions encompassing all of these other upgrades these days

The existing AVG firmware couldn't support these types of movies. It would need to implement a bank switching scheme similar to ABX. Currently it only supports a streaming mode similar to SIDE or MyIDE.

 

The fundamental requirements for RastaConverter-esque movies is a memory bank where Sally and Antic can intermix reads in a somewhat random access fashion. Ideally it would be large enough to hold both the bitmap data and the 6502 code for a full screen. Otherwise you'll have to dedicate some 6502 instructions mid-screen to bank switching and even then the underlying hardware might not be able to bank switch fast enough. ABX actually streams in the next bank during the vertical blank period.

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