Laurent Pinchart wrote: > Hi Sakari, Heippa, > On Wednesday 13 April 2011 14:16:38 Sakari Ailus wrote: >> Sung Hee Park wrote: >>> Here are two more use-cases for flash that might help inform the API >>> design. Sakari encouraged me to post these. The person writing this is >>> Andrew Adams, but I'm sending this from Sung Hee's account, because I >>> only just subscribed to linux-media and can't immediately figure out how >>> to reply to messages from before I subscribed. Sung Hee and I are both >>> grad students at Stanford who work on FCam >>> (http://fcam.garage.maemo.org/) >> >> Hi Andrew, >> >> Many thanks for the comments. >> >>> Second-curtain-sync: >>> >>> Sometimes you want to fire the flash at the end of a long exposure time. >>> It's usually a way to depict motion. Here's an example: >>> http://www.flickr.com/photos/latitudes/133206615/. >>> >>> This only really applies to xenon flashes because you can't get a crisp >>> image out of a longer duration LED flash. Even then it's somewhat >>> problematic on rolling-shutter sensors but still possible provided you >>> don't mind a slight shear to the crisp part of the image. From an API >>> perspective, it requires you to be able to specify a trigger time at >>> some number of microseconds into the exposure. On the N900 we did this >>> with a real-time thread. >>> >>> Triggering external hardware: >>> >>> This use-case is a little weirder, but it has the same API requirement. >>> Some photographic setups require you to synchronize some piece of >>> hardware with the exposure (e.g. an oscilloscope, or an external slave >>> flash). On embedded devices this is generally difficult. If you can at >>> least fire the flash at a precise delay into the exposure, you can >>> attach a photodiode to it, and use the flash+photodiode as an >>> opto-isolator to trigger your external hardware. >>> >>> So we're in favor of having user-settable flash duration, and also >>> user-settable trigger times (with reference to the start of the exposure >>> time). I'm guessing that in a SMIA++ driver the trigger time would >>> actually be a control on the sensor device, but it seemed relevant to >>> bring up while you guys were talking about the flash API. >> >> From this I reckon that in a general case the handling of the flash >> timing cannot be left for the drivers only. There must be a way to >> control it. >> >> So I'd think that also the level/edge trigger for the flash should be >> visible. On edge trigger, the only limiting factor for the flash >> duration on hardware would be the relatively coarse watchdog timer, and >> I'd think the user should be able to know that. > > I agree that the user should be able to query the limit. The limit value > should come from platform data. Agreed. >> The flash timing controls should be exposed by the sensor driver since >> the sensor is what actually performs the timing. >> >> Laurent; what do you think? > > As already discussed with you offline, I think we will need flash timing > controls on the sensor when the flash controller is configured with external > strobe in level triggered mode. I'm still not sure if the edge/level-triggered > names are the best option. They confused me in the beginning, so I find them > confusing :-) If we keep them, they will need to be very precisely documented. I'm fine with other naming --- edge/level is from the AS3645 documentation. ADP1653 does not call it with a name as far as I remember. Other similar chips can be found here: <URL:http://www.austriamicrosystems.com/eng/Products/Lighting-Management/> I tried to download the datasheets but couldn't. The AS3645 datasheet, however, is also available here: <URL:http://www.cdiweb.com/datasheets/austriamicro/AS3645_Datasheet_v1-6.pdf> Regards, -- Sakari Ailus sakari.ailus@xxxxxxxxxxxxxxxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
