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Hardware > GBA Video Capture Device

#33454 - Brian Provinciano - Mon Jan 03, 2005 7:18 pm

Hi everyone!

As some of you mgiht remember, I whipped up a little video capture device which worked on the original GB and the Game King handhelds a while back. Well, I've created a new version, which now also supports the GBA! It can display the GBA's video on the PC bit for bit perfectly (as the video signal is digital to begin with).

[Images not permitted - Click here to view it]

http://bripro.com/low/hardware/vidcap/index.php

I also posted details on the LCD and it's pinout for you other hardware hackers! (http://bripro.com/low/hardware/vidcap/index.php?page=gba)

#33468 - Lupin - Mon Jan 03, 2005 10:09 pm

wow very nice, but i wonder why do you use SRAM and not normal RAM for that device? This might be usefull for game magiznes...
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#33469 - tepples - Mon Jan 03, 2005 10:16 pm

SRAM typically needs less complex glue logic than DRAM.
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#33472 - Brian Provinciano - Mon Jan 03, 2005 11:20 pm

Thanks!

If I needed a lot of RAM (ie. megabytes), DRAM would be the best, since SRAM over 128-256KB gets really expensive. However, since I don't need that much, SRAM is much better. DRAM is multiplexed, so I'd have to do all that junk with demultiplexing, waitstates, extra latches, etc. I like to keep my devices as simple as possible.

#33482 - FluBBa - Tue Jan 04, 2005 10:31 am

Wow, nice! You have a lot of stuff going on at the same time =)
So I suppose your going to use MMC5 for Grand ThefTendo, right?
Better fix a better implemetation in PocketNES then ;)
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#33510 - Brian Provinciano - Tue Jan 04, 2005 7:49 pm

FluBBa wrote:
Wow, nice! You have a lot of stuff going on at the same time =)
So I suppose your going to use MMC5 for Grand ThefTendo, right?
Better fix a better implemetation in PocketNES then ;)


Thanks! That'd be fantastic if your added MMC5 support! I've been hoping for it for a while now :)

#33512 - tepples - Tue Jan 04, 2005 8:22 pm

PocketNES will probably never support the ExGrafix mode of MMC5 in any meaningful way, as the GBA just doesn't have enough VRAM to hold all 16384 tiles that the ExGrafix mode can address. This, along with the limited worldwide supply of MMC5 chips for replication of the NES cart, may require scaling the design down to MMC3 in the end.

Can the high-level assembler be changed to output Thumb instructions instead of 6502 instructions?
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#33518 - Lord Graga - Tue Jan 04, 2005 9:26 pm

Would you be willing to make one of these on demand?

And if yes, what price? The current "commercial" GBA video output-hardware thingies aren't very good, or so I have heard.

#33527 - Brian Provinciano - Tue Jan 04, 2005 10:36 pm

tepples: With some DMA and hblank trickery, the amount of tiles could be limited only by the GBA's system RAM. Of course, the rest of the emulator would have to be pretty optimized to take this hit.

Lord Graga: It's possible I might be able to make some to sell in the future. I plan on creating an even better one later on that will be able to display the video at the full FPS with the use of some dual port RAM, or more likely, latch trickery (this version can only run at max half the FPS, as it can't read while the video is written to the RAM, thus it must wait for a frame, then read, wait, the read, etc.)

#33528 - ampz - Tue Jan 04, 2005 10:57 pm

How do you transfer the data stream to the PC?
The parallell port can be fairly fast in EPP or ECP mode, but it is not sufficient for full framerate video.

#33530 - Brian Provinciano - Wed Jan 05, 2005 12:01 am

ampz wrote:
How do you transfer the data stream to the PC?
The parallell port can be fairly fast in EPP or ECP mode, but it is not sufficient for full framerate video.


I use EPP mode. The GB video runs at a great framerate, barely noticable that it's not the full rate. The GBA though, since it requires 240x160x16bits of transfer (76,800 bytes per frame) is a little choppier. I have a number of ideas on how to make it transfer at the full FPS. They'll be implemented in the next version.