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Heavy Stylus
Registered: Apr 2007
Posts: 61 |
Recent Diskmag with C65 FPGA Article?
Hey there! Not an ancient prod at all, but I read an article about someone creating an FPGA version of a C65 on a recent diskmag and cannot remember which one it was!
Any help would be mucho appreciated!
J/HS |
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Heavy Stylus
Registered: Apr 2007
Posts: 61 |
Many thanks Lemming! That's exactly what I was looking for. Was chatting with Lemmings creator Mike Dailly on twitter about the C65 and I mentioned this project. He wanted more info, so now I can share :) |
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hld_flt
Account closed
Registered: Nov 2014
Posts: 6 |
Feel free to tell Mike that he is welcome to prod me directly if he has any questions or would like to know more about it. Also, Lemmings is one of the test games I have been running on the C65GS to debug the VIC-IV :) |
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SIDWAVE
Account closed
Registered: Apr 2002
Posts: 2238 |
Is there any sofware collection for C65 ?
I seen 2 demos.. |
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hld_flt
Account closed
Registered: Nov 2014
Posts: 6 |
There isn't any coordinated software collection for the C65 as far as I am aware. I wrote a small demo back in 1994 which of course was never widely released, and there is quite a recent demo as well. We are going to try to get the C65GS prototype board to Revision for Easter. Maybe we will release my 1994 demo there, and aim for some sort of "longest delay between writing and releasing demo" prize ;) |
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Oswald
Registered: Apr 2002
Posts: 5017 |
I'd buy a c65 fpga. any readable HW specs somewhere? btw fuck commodore for not doing a proper c64 follow up. the c65 alone could have crushed the amiga. if only it was done in time... |
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Rayne
Account closed
Registered: Jan 2002
Posts: 30 |
Take a look here for the original system specification and some other stuff: http://www.zimmers.net/anonftp/pub/cbm/c65/ |
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Oswald
Registered: Apr 2002
Posts: 5017 |
really nice hw. I wonder if DAT only helps in adress calcs of 1 bitplane, or does it do c2p too ? :) or how far fine scrolling can go ? attributed bitplane is not explained fully either, does it work like a vICII bitplane ? what if other bitplanes are turned on too ? |
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hld_flt
Account closed
Registered: Nov 2014
Posts: 6 |
Bit planes in the C65's VIC-III were horrible. The fine scrolling was only got for displays only somewhat larger than the screen. The DAT was an abomination necessitated by the use of bitplanes, and was horribly slow. It was generally faster to use the CPU instead. This is why the C65GS doesn't do bit-planes, instead opting for 256-colour character mode. It's also more memory efficient, because you can reuse empty blocks, instead of wasting 10s of KB in a game display with blank space. |
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Oswald
Registered: Apr 2002
Posts: 5017 |
how does 256 charmode work? btw its not like games used heavily bitplanes on the c64 either. I just wondered if the fine scroll is wide enough, there would be time to 2buffer nicely for scrolling. also what does DAT exactly do? and why is it slow? its slower to set up coords, than just sta sta ? |
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hld_flt
Account closed
Registered: Nov 2014
Posts: 6 |
Sorry for extreme delay in response.
On a real C65 there is neither memory nor CPU time to effectively double-buffer in a game.
The DAT lets you specify an 8-bit X and Y coordinate in two registers, and then access the (upto 8) bitplane bytes for those coordinates directly.
Of course, you still have to do the bit fiddling, so changing a single pixel is still horribly slow.
Even assuming you could use DMA to write to the 8 bytes in 8 cycles, modifying a 256-colour pixel requires 8 cycles, and more like 100 or more cycles in reality. Since you have only 3.5MHz/50Hz = 70K cycles per frame, you are limited to updating never more than 10K pixels per frame using unrealistically optimistic appraisal. More realistically you could update not more than a few hundred pixels per cycle.
There was also as I recall some funny number of cycles you had to wait after setting the DAT address before you could use it for the new address.
I understand why they created it, but it was a partial mitigation of the bigger problems that bitplanes presented on the machine.
Of course, with the technology of the time, they might not have had too many other options, but I do :) |
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