Re: DMA to user space for framegrabber HOW?

Alan Cox (alan@lxorguk.ukuu.org.uk)
Fri, 4 Jun 1999 15:41:30 +0100 (BST)


> maximum number of frames/s out of it. If I remember correctly, the solution
> was to mmap the user space buffer to kernel space and then DMA to that.

You map kernel space into user memory and then DMA into kernel space.

> Is there example code? What if I wish to use th MIT SHM extension for X to
> transfer the data to the X framebuffer? Is it possible this way to

If the card can do clever stuff (eg like the TV capture cards) you want to
DMA direct to frame buffer when possible.

> card (which is also PCI of course)? The data doesn't need to be processed,
> the framegrabber hardware arranges things to that the data is already in the
> right format needed for X.

Take a look at the video4linux api and the bttv and zoran chip drivers

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