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PostPosted: Sun Jul 09, 2017 12:37 pm 
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Location: Germany
hi folks
iam new to the c64 scene and have a question.

Would it be possible to use a SuperGameboy to play Gameboy cartridges on a C64? (no emulation)

I have some experience with old video game consoles like NES / SNES /GB

the following data i collected makes me think it should be possible.

https://pastebin.com/vEEqZSP4

in short

use memory expasion port on the C64 to

-read SuperGameboy v-ram and recolor it.
-send control commands to Supergameboy

Do I miss something or is that really possible?


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PostPosted: Sun Jul 09, 2017 1:15 pm 
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Is the pixel format from the SGB compatible with what the VIC-2 expects? It seems like you might not have enough time to copy and repack the video, if not...


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PostPosted: Sun Jul 09, 2017 1:56 pm 
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the Vram of the SGB contains 2BPP data but i dont know if the VIC-II can handel this ?

Image

The MCI mode of the C64 should be suitable for this application but that is just my guess.

2BPP= 4 colors/shades of grey

C64 MCI mode generates 320*200 pixel resolution with 4 colors per 8x8 cell.


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PostPosted: Sun Jul 09, 2017 2:14 pm 
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To the best of my memory, the SNES packs pixels as:
abcdefgh ABCDEFGH

while the VIC-2 (in 2bpp mode) packs pixels as:
AaBbCcDd EeFfGgHh

so ... you might have your work cut out for you.

It's possible (no promises) that clever rewiring of the data bus to the SGB would make it easier. (You don't have to connect D1 to D1, &c)


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PostPosted: Sun Jul 09, 2017 2:50 pm 
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Joined: Sun Sep 19, 2004 11:12 pm
Posts: 19332
Location: NE Indiana, USA (NTSC)
Rewire the bus
Code:
abcdefgh -> aebfcgdh

Read pixels
Code:
aebfcgdh
AEBFCGDH

mask off bits
Code:
a0b0c0d0
0e0f0g0h
A0B0C0D0
0E0F0G0H

shift bits
Code:
0a0b0c0d
0e0f0g0h
A0B0C0D0
E0F0G0H0

OR them together and write them to video memory
Code:
A0B0C0D0 | 0a0b0c0d = AaBbCcDd
E0F0G0H0 | 0e0f0g0h = EeFfGgHh

I have no idea how quickly that can be done for the 5760 bytes in the SGB frame buffer.

But it would stretch the picture from the SGB pixel aspect ratio 8:7 to the C64 multicolor pixel aspect ratio 3:2, making everything 31% wider.


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PostPosted: Sun Jul 09, 2017 3:02 pm 
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yes i think i have read something like that on

http://www.studiostyle.sk/dmagic/gallery/gfxmodes.htm

Quote:
This mode uses two MultiColor pictures (160*200/4 colors in 4*8 cell), each using its own attributes


the SGB uses 160 × 144 in 8*8 cell (see picture in 3. post)


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PostPosted: Sun Jul 09, 2017 3:13 pm 
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It's much easier to do that in a hardware fashion, really, since you then don't have any AND nor ORing, just a matter of what's being written or read.

I know of a relevant patent. Consider the "prior art" description.


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PostPosted: Sun Jul 09, 2017 3:30 pm 
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The 33% wider screen only applies to NTSC C64 ,for PAL C64 it's only 6,8% wider wich is acceptable i think

1:1 Ratio

Image

1:0.75 ratio (133%) NTSC C64

Image

1:0.936 ratio (106.8%) PAL C64

Image


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PostPosted: Sun Jul 09, 2017 3:52 pm 
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Location: Rio de Janeiro - Brazil
The NTSC simulation doesn't look any worse than 4:3 content stretched to 16:9, something I see a lot of people doing (makes me cringe a bit, but it doesn't seem like a big deal to many people). If that's the price to pay for doing something cool like playing games for one retro machine on another retro machine, I think it's fine.


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PostPosted: Thu Jul 27, 2017 2:44 am 
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Location: Chexbres, VD, Switzerland
tokumaru wrote:
The NTSC simulation doesn't look any worse than 4:3 content stretched to 16:9, something I see a lot of people doing (makes me cringe a bit, but it doesn't seem like a big deal to many people).

Agreed. How many youtube videos about retro games have them incorrectly converted to 16:9 format ?

Besides, does the C64 even have 2 shades of gray in the 1st place ? Or would any dark colour and any light colour do the job ?

I think a SGB on a C64 would be very cool to see !


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PostPosted: Thu Jul 27, 2017 7:32 am 
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The C64 has a (comparatively) whopping 3 shades of grey, plus black and white.

_________________
http://www.chrismcovell.com


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PostPosted: Thu Jul 27, 2017 11:29 am 
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Lack of grays isn't a problem, GB video looks good in all kinds of colored gradients.


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