Date: Mon, 14 Jul 2003 09:55:40 -0700 From: John-Mark Gurney <gurney_j@efn.org> To: Andrew Gordon <arg-bsd@arg1.demon.co.uk> Cc: multimedia@freebsd.org Subject: Re: AW: BSD video capture emulation question Message-ID: <20030714165540.GU35337@funkthat.com> In-Reply-To: <20030714152113.O81987-100000@server.arg.sj.co.uk> References: <20030714064137.GT35337@funkthat.com> <20030714152113.O81987-100000@server.arg.sj.co.uk>
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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 > possibilities: > > 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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