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List:       linux-video
Subject:    [video4linux] API
From:       Alan Cox < alan () cymru ! net>
Date:       1998-05-16 15:04:20

I've added a draft API definition to the video4linux web page 
(http://roadrunner.swansea.uk.linux.org/v4l.shtml). It doesnt yet define
the innards of the mmap API. 

There are two things I need to add to the API that I can see

1.	VIDIOCGMMAPINFO

	Return a structure giving the number of buffered frames, the 
	mmap area size to use  and the offset of each frame.

2.	VIDIOCGDEVS

	So for any device you can say 'ok so which teletext/vbi/radio/mixer'
	are the same piece of equipment as the device Im talking to now.


Alan
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List:       linux-video
Subject:    Re: [video4linux] API
From:       Gerd Knorr <kraxel () goldbach ! isdn ! cs ! tu-berlin ! de>
Date:       1998-05-28 19:23:12

In lists.linux.video4linux you write:

>I've added a draft API definition to the video4linux web page 
>(http://roadrunner.swansea.uk.linux.org/v4l.shtml). It doesnt yet define
>the innards of the mmap API. 

>There are two things I need to add to the API that I can see

>1.	VIDIOCGMMAPINFO

>	Return a structure giving the number of buffered frames, the 
>	mmap area size to use  and the offset of each frame.

Is'nt just the size and number of frames enouth?  Or we return max.
number of frames and max. mmap area size and allow the application
to set the buffer size per frame.  That way one can have many small
or a few large buffers.


Another problem:

The current VIDEOCSYNC handling is IMHO not very good at the moment.
How about adding a argument to the ioctl?  The frame number (the same
as in video_mmap.frame)?  That way it is very easy for the driver to
decide whever this frame...

	... is already available => return
	... is'nt available yet (bt848 still busy) => block until
	    it is available
	... was'nt asked for (using capture ioctl) => -EINVAL

That would make the whole thing more robust.  Currently both the driver
and application have to count the (successful) capture and sync ioctls.
And if one does a mistake, you might get gibbish becauce they ar'nt in
sync any more.

Comments?

  Gerd

>(http://roadrunner.swansea.uk.linux.org/v4l.shtml). It doesnt yet define
>the innards of the mmap API. 

>There are two things I need to add to the API that I can see

>1.	VIDIOCGMMAPINFO

>	Return a structure giving the number of buffered frames, the 
>	mmap area size to use  and the offset of each frame.

>2.	VIDIOCGDEVS

>	So for any device you can say 'ok so which teletext/vbi/radio/mixer'
>	are the same piece of equipment as the device Im talking to now.


>Alan
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-- 
Gerd Knorr <kraxel@cs.tu-berlin.de>
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List:       linux-video
Subject:    Re: [video4linux] API
From:       Alan Cox <alan () cymru ! net>
Date:       1998-06-01 15:40:56

> Is'nt just the size and number of frames enouth?  Or we return max.
> number of frames and max. mmap area size and allow the application
> to set the buffer size per frame.  That way one can have many small
> or a few large buffers.

That isnt a bad idea. However some cards of constraints on alignment
to page or multipage boundaries, so we need some flexibility

> and application have to count the (successful) capture and sync ioctls.
> And if one does a mistake, you might get gibbish becauce they ar'nt in
> sync any more.

Sounds great to me - got a patch for this ?

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List:       linux-video
Subject:    Re: [video4linux] API
From:       Gerd Knorr < kraxel () goldbach ! isdn ! cs ! tu-berlin ! de>
Date:       1998-06-01 21:40:20
[Download message RAW]

On Mon, 1 Jun 1998, Alan Cox wrote:

> > Is'nt just the size and number of frames enouth?  Or we return max.
> > number of frames and max. mmap area size and allow the application
> > to set the buffer size per frame.  That way one can have many small
> > or a few large buffers.
> 
> That isnt a bad idea. However some cards of constraints on alignment
> to page or multipage boundaries, so we need some flexibility

I like the OSS way to handle this:  If some application change some
parameters, the driver returns the value really used.  That way the driver
can round up to page boundaries or whatever without problems. 

> > and application have to count the (successful) capture and sync ioctls.
> > And if one does a mistake, you might get gibbish becauce they ar'nt in
> > sync any more.
> 
> Sounds great to me - got a patch for this ?

Hacked up one today.  patch against 0.5.8.  Started to move the tv norm to
video_channel too.  The #ifdef'ed out code in ioctl VIDIOCSCHAN oopses for
some reason I hav'nt tracked down yet.

  Gerd


Patch
 
 

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