Hi Nayden,
On Tuesday 05 April 2011 17:07:41 Nayden Kanchev wrote:
> On 04/05/2011 04:35 PM, Sakari Ailus wrote:
> > Laurent Pinchart wrote:
> >> On Tuesday 05 April 2011 13:21:03 Sakari Ailus wrote:
> >>> Laurent Pinchart wrote:
> >>>> On Tuesday 05 April 2011 12:23:51 Sakari Ailus wrote:
> >>>>> Sakari Ailus wrote:
> >>>>>> Laurent Pinchart wrote:
> >>>>>>> On Wednesday 30 March 2011 13:05:54 Sakari Ailus wrote:
> >>>>>>>> Laurent Pinchart wrote:
> >>>>>>>>> On Monday 28 March 2011 14:55:40 Sakari Ailus wrote:
> >>>>>>>>>
> >>>>>>>>> [snip]
> >>>>>>>>>
> >>>>>>>>>> V4L2_CID_FLASH_STROBE_MODE (menu; LED)
> >>>>>>>>>>
> >>>>>>>>>> Use hardware or software strobe. If hardware strobe is selected,
> >>>>>>>>>> the flash controller is a slave in the system where the sensor
> >>>>>>>>>> produces the strobe signal to the flash.
> >>>>>>>>>>
> >>>>>>>>>> In this case the flash controller setup is limited to
> >>>>>>>>>> programming strobe timeout and power (LED flash) and the sensor
> >>>>>>>>>> controls the timing and length of the strobe.
> >>>>>>>>>>
> >>>>>>>>>> enum v4l2_flash_strobe_mode {
> >>>>>>>>>>
> >>>>>>>>>> V4L2_FLASH_STROBE_MODE_SOFTWARE,
> >>>>>>>>>> V4L2_FLASH_STROBE_MODE_EXT_STROBE,
> >>>>>>>>>>
> >>>>>>>>>> };
> >>>>>>>>>
> >>>>>>>>> [snip]
> >>>>>>>>>
> >>>>>>>>>> V4L2_CID_FLASH_LED_MODE (menu; LED)
> >>>>>>>>>>
> >>>>>>>>>> enum v4l2_flash_led_mode {
> >>>>>>>>>>
> >>>>>>>>>> V4L2_FLASH_LED_MODE_FLASH = 1,
> >>>>>>>>>> V4L2_FLASH_LED_MODE_TORCH,
> >>>>>>>>>>
> >>>>>>>>>> };
> >>>>>>>>>
> >>>>>>>>> Thinking about this some more, shouldn't we combine the two
> >>>>>>>>> controls ? They are basically used to configure how the flash
> >>>>>>>>> LED is controlled: manually (torch mode), automatically by the
> >>>>>>>>> flash controller (software strobe mode) or automatically by an
> >>>>>>>>> external component (external strobe mode).
> >>>>>>>>
> >>>>>>>> That's a good question.
> >>>>>>>>
> >>>>>>>> The adp1653 supports also additional control (not implemented in
> >>>>>>>> the driver, though) that affect hardware strobe length. Based on
> >>>>>>>> register setting, the led will be on after strobe either until
> >>>>>>>> the timeout expires, or until the strobe signal is high.
> >>>>>>>>
> >>>>>>>> Should this be also part of the same control, or a different one?
> >>>>>>>
> >>>>>>> That can be controlled by a duration control. If the duration is 0,
> >>>>>>> the flash is lit for the duration of the external strobe, otherwise
> >>>>>>> it's lit for the programmed duration.
> >>>>>>
> >>>>>> Sounds good to me.
> >>>>>
> >>>>> Thinking about this again; there won't be a separate duration control
> >>>>
> >>>> Why not ? I think we need two timeouts, a watchdog timeout to prevent
> >>>> flash fire or meltdown, and a normal timeout to lit the flash for a
> >>>> user-selected duration.
> >>>
> >>> Let's assume that an application wants to expose a frame using flash
> >>> with software strobe.
> >>>
> >>> 1. strobe flash
> >>> 2. qbuf
> >>> 3. streamon
> >>> 4. dqbuf
> >>> 5. streamoff
> >>> 6. ...
> >>>
> >>> How does an application know how long is the time between 1 -- 4? I'd
> >>> guess that in 6 the application would like to switch off the flash
> >>> instead of specifying a timeout for it.
> >>
> >> That's a valid use case, and we need to support it. It requires a way to
> >> lit the flash with no timeout other than the watchdog timeout, and a
> >> way to turn it off.
> >>
> >> However, I'm not sure we should rule out the usefulness of a
> >> duration-based software flash strobe. Can't the two APIs coexist ? Or
> >> do you think a duration-based API is useless ?
> >
> > I don't want to rule it out, but I don't see use for it either for the
> > time being and thus don't see a reason to specify an API for it. The
> > adp1653 driver does not implement a software based shutdown timeout and
> > I'm not aware of others implementing it either. It was just an idea to
> > overcome the coarse hardware watchdog timeout.
> >
> > If there is use for it then I think we could bring up the question
> > again: use V4L2_CID_FLASH_TIMEOUT or create V4L2_CID_FLASH_DURATION for
> > it.
> >
> > What do you think?
>
> According to me it is a matter of choice whether flash will be started
> and stopped explicitly or timer will be used.
>
> My personal opinion is that both APIs could coexist although I wouldn't
> use timebased approach. The problem is that timeout should be always a
> little bit higher than actual required time (Sensor frame rate + sensor
> exposure time) because some delays are expected from starting the flash
> till starting the camera. Those delay could vary depending on the
> implementation and could be several ms. In that case flash will stop
> before sensor is ready. So as result half bright half dark images will
> be captured.
>
> On the other hand if timer is used for stopping it that would optimize
> the flash usage and lower flash duty cycle. That on the other hand will
> lead to smaller cooldown time required between two consecutive captures.
>
> So I would go with the explicit control over the flash, since timebased
> approach has several variable in the calculations.
OK, I surrender :-)
I'm then fine with an explicit on/off API for software strobe. If we need a
duration-based API later we will just introduce a new control.
--
Regards,
Laurent Pinchart
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