Re: [Gumstix-users] Video capture application

[Pascal A. B. <pas...@wa...>]

Alexandre Pereira Nunes writes:
 > What about DMA? I guess it would be nice if the frame grabber writes
 > direct on memory (through a buffer), and when i.e. a scanline is
 > complete, it triggers an irq on the cpu. That would be close to optimal,
 > i guess. I read somewhere that there are missing line(s) on the 92 pin
 > connector in order to do dma, is that so?

I once mentioned that DREQ was apparently missing.

As far as I understand the PXA specs, if the sensor could signal
that data is available by asserting DREQ, then the DMAC would read
it immediately.  So you could have a much smaller FIFO.

I'm not sure what the bandwidth would be, though.  DREQ must remain
high for 4 MEMCLKs to start a transaction, and low for 4 MEMCLKs
afterward.  Hopefully up to 32 bytes could be transferred per burst.

But you can do DMA without DREQ, of course.

-- Pascal