AW: BSD video capture emulation question
gurney_j at efn.org
Mon Jul 14 09:56:40 PDT 2003
Andrew Gordon wrote this message on Mon, Jul 14, 2003 at 16:29 +0100:
> On Sun, 13 Jul 2003, John-Mark Gurney wrote:
> > If the mbuf code seperated it out, this MIGHT be a possibility, I'm
> > pretty sure we don't want to run into some of the problem with resource
> > contention on mbufs.. Also, the buffer space may need more fine
> > management... The idea of a sink sending a packet that a source fills
> > also is kinda wierd (necessary for some dma operations)..
> There seems to be some lack of clarity in these discussions about what
> level of API you are trying to create. There's at least two
> a) The low-level API for shifting bulk data and timing information
> between hardware devices and/or processing modules. Here the
> device drivers and encoders/decoders are the providers and consumers
> of the API, and we're inevitably talking about a kernel interface.
> b) A higher level API to control the 'plumbing'. Here, user-interface
> programs are the consumer of the API, with the details of the
> bulk transfer mechanisms being hidden below the API.
> Then there's your stated aim that things like USB videocams shouldn't have
> to be implemented with all the logic in the kernel (an aim I agree with
> BTW). So, you end up with several different APIs for the core data
> transfer, with scope for a unifying higher-layer API on top. But it's a
> lot of work....
Thank you for clarifing this for everyone. Yes, I plan to try to address
both a and b of above. Right now my priority is a since that will get
most hardware available, but b is necessary in order to properly and fully
support userland devices. B is also necessary because I plan to implement
a in such a way that programmers will kill me if b doesn't come around.
The reason I say this is that the hardware interface will probably have
five different fd's for a card like an MJPEG card. Remebering what
ioctl's for what fd is to be simplifed by b. I have recently changed
the verbage of: http://people.freebsd.org/~jmg/videobsd.html
to make this more clear.
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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