Re: [RFC] How to get current position/status of iris/focus/pan/tilt/zoom?

[Hans Verkuil <hverkuil@xs4all.nl>]

On 07/22/15 10:21, Sakari Ailus wrote:
> Hi Hans,
> 
> On Thu, Jul 02, 2015 at 02:00:23PM +0200, Hans Verkuil wrote:
>> When using V4L2_CID_IRIS/FOCUS/PAN/TILT/ZOOM_ABSOLUTE/RELATIVE, how do you know
>> when the new position has been reached? If this is controlled through a motor,
>> then it may take some time and ideally you would like to be able to get the
>> current absolute position (if the hardware knows) and whether the final position
>> has been reached or not.
> 
> On voice coil lenses it's also not possible to know when the position has
> been reached, however you can estimate when it has happened based on the
> intended movement and algorithm used to move the lens. This is far from
> trivial though.
> 
> For low-level lends drivers knowing where the lens is is not feasible IMO at
> the moment.
> 
>>
>> In addition, it should be possible to raise fault conditions.
> 
> Do you know of hardware that can do this? The only non-buffer related
> devices that can do this I'm aware of are flash controllers.

If a motor is involved to move things around, then that motor can cause
failures that you want to signal. For example if something is blocking the
motor from moving any further, overheating, whatever. I hate moving parts :-)

> I'd only define them if there's actual hardware that can actually raise
> these conditions.
> 
>>
>> The way the ABSOLUTE controls are defined is ambiguous since it doesn't say
>> anything about what it returns when you read it: is that the current absolute
>> position, or the last set absolute position? I suspect it is the second one.
> 
> I wonder if this has been really well thought out when the controls were
> defined. I share your assumption.
> 
>> If it is the second one, then I propose a V4L2_CID_IRIS_CURRENT control (and
>> ditto for the other variants) that is a read-only control returning the current
>> position with the same range and unit as the ABSOLUTE control.
> 
> This makes perfect sense if you have hardware that can tell the current
> position.
> 
> Only one of the RELATIVE and ABSOLUTE controls should be implemented. I
> guess no driver in mainline would implement both,

That makes sense.

> I've seen such outside
> mainline though. :-)
> 
>>
>> For the status/fault information I think the V4L2_CID_AUTO_FOCUS_STATUS comes
>> close, but it is too specific for auto focus. For manually positioning things
>> this might be more suitable:
>>
>> V4L2_CID_IRIS_STATUS	bitmask
>>
>> 	V4L2_IRIS_STATUS_MOVING (or perhaps _BUSY?)
>> 	V4L2_IRIS_STATUS_FAILED
>>
>> And ditto for the other variants.
> 
> If you have hardware that can give you the information, sure.
> 
>> Interaction between V4L2_CID_FOCUS_STATUS and AUTO_FOCUS_STATUS:
>>
>> If auto focus is enabled, then FOCUS_STATUS is always 0, if auto focus is
>> disabled, then AUTO_FOCUS_STATUS is always IDLE.
> 
> Looks good to me.
> 

Thanks!

	Hans