SD Gecko and DMA

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piratesephiroth
Posts: 52
Joined: Sun Mar 24, 2013 4:59 pm

SD Gecko and DMA

Post by piratesephiroth » Fri Oct 18, 2013 5:14 pm

Recently someone made another thread about some game not running properly through SD Gecko, and grumpy hacktivist/homebrew developer and celebrity tueidj made another sarcastic post:
tueidj wrote:Build your own combination USB/SD gecko that doesn't suck, you know you want to.
Soon, good guy emu_kidid replied
emu_kidid wrote:I know I want to and it shouldn't be too hard to do but I'd need to learn hardware pretty much from scratch at this point.
So now I ask:
Is there any existing homebrew that doesn't use PIO for SD Gecko? I don't remember any.
Is there even any proof-of-concept code for that?
tueidj
Posts: 564
Joined: Fri May 03, 2013 6:57 am

Re: SD Gecko and DMA

Post by tueidj » Fri Oct 18, 2013 10:22 pm

The code is easy, having hardware that uses the EXI interrupt line is what's missing. Somebody made some prototypes a few years ago but it never went further.
piratesephiroth
Posts: 52
Joined: Sun Mar 24, 2013 4:59 pm

Re: SD Gecko and DMA

Post by piratesephiroth » Fri Oct 18, 2013 11:35 pm

Ah, so it is impossible with a simple 'straight through' memory card to SD adapter...
We're gonna need an SD Gecko v2.
tueidj
Posts: 564
Joined: Fri May 03, 2013 6:57 am

Re: SD Gecko and DMA

Post by tueidj » Sat Oct 19, 2013 12:19 am

Just to be clear the interrupt line isn't necessary for DMA transfers, but without it you need to poll to check if the transfer has finished so it's still basically PIO.
For USB gecko, even if it supported interrupts DMA would be practically unusable since the send/receive/flash write/flash read commands only support one byte at a time.
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