Re: [livid-gatos] [RFC] alternative kernel multimedia API

[Nate Dannenberg]

On Thu, 25 Oct 2001 [e-mail] wrote:

>
>  After looking at and working with Xv, v4l and v4l2 I became somewhat
> dissatisfied with the current state of affairs. I have attached a
> description of the API that would make (at least) me much happier.
>
>  I would very much appreciate comments from interested people..

I'm not a coder for Linux or X, but I figured this would be a good read
anyway, as it might provide some ideas for a similar (albeit less complex)
issue on another platform I use >:-)

Anyways since this is an RFC, here's the only a couple of comments I can
think of (the RFC otherwise looks clear to me):

Commands/queries should also include some kind of (arbitrary, decided by the
calling program) command serial number, so that an out-of-sequence reply
(those prepended with a colon as you describe) can be matched to a previous
command/query.  This could allow several commands to be sent and handled by
multiple processes/threads/whatever.

 05,HUE=7\n
 07,some unrelated command
+05\n				# The HUE command was successful
:07,reply to unrelated command
:05,HUE=6\n			# Driver reported the HUE parameter as
				# different from that most recently set.

The program wanted to set HUE to 7, command successful, value later returned
was 6 (maybe the device only allows even values), while at the same time some
other command was sent and processed.

Also, it might be a nice idea to return the range of one or more parameters if
a command given is out of range.  Suppose HUE is only valid for values 0-255:

 06,HUE=300\n
-06,HUE=INVALID,0,255\n

..Would tell the calling program that a value given for HUE is only valid for
a range of 0 to 255.  This would be useful for a program that wants to attempt
to guess the range a device accepts for a given parameter.

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