Conventional structure for 18k and bigger images?

Talk about programming CreatiVision (except games programming). Projects of homebrew hardware are also welcome.
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Fabrizio Caruso
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Conventional structure for 18k and bigger images?

Post by Fabrizio Caruso » Fri Jul 17, 2020 8:57 pm

Hi everyone,

what structure do emulators (such as Mame or Mess) conventionally expect for 18k and bigger rom images?
For 16k I know I need to invert the two 8k blocks.
What should I do for 18k images? and for bigger images? What is the maximum size I can have on an emulator and or real hardware equipped with special multi-card?
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Scouter3d
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Re: Conventional structure for 18k and bigger images?

Post by Scouter3d » Sat Jul 18, 2020 11:30 am

Hi Fabrizio,
here are my 2 cents...

The Creativision can use a maximum of 32kb cartridge (2*16Kb blocks) (i guess the emulators do so as well)

As i understand Mame uses cart images, that reflect the original physical cartridge, as many cartridges on the Creativison use 2 smaller ROM chips instead of 1 big chip, Mame wants the files also split into according pieces...
I guess it was cheaper in production to use 2x4k, 2x8k, 1x8+1x4 instead of one bigger chip...
If an original cart uses 2 chips these 2 banks are selected on the Creativision by the ChipselectSignal /ROM1 ($8000-$BFFF) and /ROM2 ($4000-$7FFF) (more or less Addresslines 14 and 15)
AFAIK this is the only "addressflipping the real CV hardware does as ROM2 is the lower memoryaddress than ROM1

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Fabrizio Caruso
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Joined: Mon Feb 05, 2018 9:23 am
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Re: Conventional structure for 18k and bigger images?

Post by Fabrizio Caruso » Wed Jul 29, 2020 6:13 pm

So, if I create a cartridge image, I need to swap the 2 16kb blocks, i.e., the higher block should come before the lower one. When I try to load such a cartridge I get an error in Mame/Mess about its size:
Fatal error: Device CreatiVision Cartridge Slot load failed: Image extends beyond the expected size for an APF cart

I get a similar error if I use a 24 images where I put the first 8k at the end.

If I create a 18k image where I put the first 8k block at the end, I get a white frozen screen.

So far, I have only managed to get 8k and 16k (swapped 8k blocks) to work.

My non-working experiments are in:
https://github.com/Fabrizio-Caruso/CROS ... uilds#L254

My working cases are in:
https://github.com/Fabrizio-Caruso/CROS ... rgets#L388
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Scouter3d
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Re: Conventional structure for 18k and bigger images?

Post by Scouter3d » Sat Aug 01, 2020 11:04 am

Hi,

i think part of the problem (the biggest part) is the MAME/MESS emulation itself, as there are no 32kb original carts...
maybe there is a need to define a 2*16kb cartridge scheme for MAME

the real hardware has no problem with the 32kb...

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