Re: VIC and Matrox Meteor

Stephen Williams (steve@icarus.icarus.com)
Fri, 19 Sep 1997 23:15:40 +0800


kraxel@goldbach.isdn.cs.tu-berlin.de said:
> As far I can see, the main problem are the mm tricks. The card needs
> some memory where it can transfer the image to (using DMA). As far I
> know, there are two ways to do this:

Some of the devices I write linux drivers for deliver images to the host
at pretty high speed. I have allocated kernel memory with get_free_page
to serve this purpose. It is generally better if the board in question
can support DMA chaining so that you can allocate lots of pages.

I have found that allocating a bunch of pages and allowing the user
mode process to mmap that memory works well enough. Think of it as a
virtual frame buffer for a frame grabber. The problem with this is of course
that you need the physical memory available. (Then again, the hardware
really requires that to be the case anyhow.

-- 
Steve Williams
steve@icarus.com
steve@picturel.com

"The woods are lovely, dark and deep. But I have promises to keep, And lines to code before I sleep, And lines to code before I sleep."