189 lines
6.2 KiB
ReStructuredText
189 lines
6.2 KiB
ReStructuredText
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.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
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.. _flash-controls:
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***********************
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Flash Control Reference
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***********************
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The V4L2 flash controls are intended to provide generic access to flash
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controller devices. Flash controller devices are typically used in
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digital cameras.
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The interface can support both LED and xenon flash devices. As of
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writing this, there is no xenon flash driver using this interface.
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.. _flash-controls-use-cases:
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Supported use cases
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===================
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Unsynchronised LED flash (software strobe)
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------------------------------------------
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Unsynchronised LED flash is controlled directly by the host as the
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sensor. The flash must be enabled by the host before the exposure of the
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image starts and disabled once it ends. The host is fully responsible
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for the timing of the flash.
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Example of such device: Nokia N900.
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Synchronised LED flash (hardware strobe)
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----------------------------------------
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The synchronised LED flash is pre-programmed by the host (power and
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timeout) but controlled by the sensor through a strobe signal from the
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sensor to the flash.
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The sensor controls the flash duration and timing. This information
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typically must be made available to the sensor.
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LED flash as torch
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------------------
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LED flash may be used as torch in conjunction with another use case
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involving camera or individually.
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.. _flash-control-id:
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Flash Control IDs
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-----------------
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``V4L2_CID_FLASH_CLASS (class)``
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The FLASH class descriptor.
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``V4L2_CID_FLASH_LED_MODE (menu)``
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Defines the mode of the flash LED, the high-power white LED attached
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to the flash controller. Setting this control may not be possible in
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presence of some faults. See V4L2_CID_FLASH_FAULT.
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.. tabularcolumns:: |p{5.7cm}|p{11.8cm}|
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.. flat-table::
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:header-rows: 0
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:stub-columns: 0
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* - ``V4L2_FLASH_LED_MODE_NONE``
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- Off.
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* - ``V4L2_FLASH_LED_MODE_FLASH``
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- Flash mode.
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* - ``V4L2_FLASH_LED_MODE_TORCH``
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- Torch mode.
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See V4L2_CID_FLASH_TORCH_INTENSITY.
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``V4L2_CID_FLASH_STROBE_SOURCE (menu)``
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Defines the source of the flash LED strobe.
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.. tabularcolumns:: |p{7.5cm}|p{7.5cm}|
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.. flat-table::
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:header-rows: 0
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:stub-columns: 0
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* - ``V4L2_FLASH_STROBE_SOURCE_SOFTWARE``
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- The flash strobe is triggered by using the
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V4L2_CID_FLASH_STROBE control.
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* - ``V4L2_FLASH_STROBE_SOURCE_EXTERNAL``
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- The flash strobe is triggered by an external source. Typically
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this is a sensor, which makes it possible to synchronise the
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flash strobe start to exposure start.
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``V4L2_CID_FLASH_STROBE (button)``
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Strobe flash. Valid when V4L2_CID_FLASH_LED_MODE is set to
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V4L2_FLASH_LED_MODE_FLASH and V4L2_CID_FLASH_STROBE_SOURCE
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is set to V4L2_FLASH_STROBE_SOURCE_SOFTWARE. Setting this
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control may not be possible in presence of some faults. See
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V4L2_CID_FLASH_FAULT.
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``V4L2_CID_FLASH_STROBE_STOP (button)``
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Stop flash strobe immediately.
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``V4L2_CID_FLASH_STROBE_STATUS (boolean)``
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Strobe status: whether the flash is strobing at the moment or not.
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This is a read-only control.
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``V4L2_CID_FLASH_TIMEOUT (integer)``
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Hardware timeout for flash. The flash strobe is stopped after this
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period of time has passed from the start of the strobe.
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``V4L2_CID_FLASH_INTENSITY (integer)``
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Intensity of the flash strobe when the flash LED is in flash mode
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(V4L2_FLASH_LED_MODE_FLASH). The unit should be milliamps (mA)
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if possible.
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``V4L2_CID_FLASH_TORCH_INTENSITY (integer)``
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Intensity of the flash LED in torch mode
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(V4L2_FLASH_LED_MODE_TORCH). The unit should be milliamps (mA)
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if possible. Setting this control may not be possible in presence of
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some faults. See V4L2_CID_FLASH_FAULT.
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``V4L2_CID_FLASH_INDICATOR_INTENSITY (integer)``
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Intensity of the indicator LED. The indicator LED may be fully
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independent of the flash LED. The unit should be microamps (uA) if
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possible.
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``V4L2_CID_FLASH_FAULT (bitmask)``
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Faults related to the flash. The faults tell about specific problems
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in the flash chip itself or the LEDs attached to it. Faults may
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prevent further use of some of the flash controls. In particular,
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V4L2_CID_FLASH_LED_MODE is set to V4L2_FLASH_LED_MODE_NONE
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if the fault affects the flash LED. Exactly which faults have such
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an effect is chip dependent. Reading the faults resets the control
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and returns the chip to a usable state if possible.
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.. tabularcolumns:: |p{8.4cm}|p{9.1cm}|
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.. flat-table::
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:header-rows: 0
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:stub-columns: 0
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* - ``V4L2_FLASH_FAULT_OVER_VOLTAGE``
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- Flash controller voltage to the flash LED has exceeded the limit
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specific to the flash controller.
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* - ``V4L2_FLASH_FAULT_TIMEOUT``
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- The flash strobe was still on when the timeout set by the user ---
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V4L2_CID_FLASH_TIMEOUT control --- has expired. Not all flash
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controllers may set this in all such conditions.
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* - ``V4L2_FLASH_FAULT_OVER_TEMPERATURE``
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- The flash controller has overheated.
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* - ``V4L2_FLASH_FAULT_SHORT_CIRCUIT``
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- The short circuit protection of the flash controller has been
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triggered.
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* - ``V4L2_FLASH_FAULT_OVER_CURRENT``
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- Current in the LED power supply has exceeded the limit specific to
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the flash controller.
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* - ``V4L2_FLASH_FAULT_INDICATOR``
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- The flash controller has detected a short or open circuit
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condition on the indicator LED.
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* - ``V4L2_FLASH_FAULT_UNDER_VOLTAGE``
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- Flash controller voltage to the flash LED has been below the
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minimum limit specific to the flash controller.
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* - ``V4L2_FLASH_FAULT_INPUT_VOLTAGE``
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- The input voltage of the flash controller is below the limit under
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which strobing the flash at full current will not be possible.The
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condition persists until this flag is no longer set.
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* - ``V4L2_FLASH_FAULT_LED_OVER_TEMPERATURE``
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- The temperature of the LED has exceeded its allowed upper limit.
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``V4L2_CID_FLASH_CHARGE (boolean)``
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Enable or disable charging of the xenon flash capacitor.
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``V4L2_CID_FLASH_READY (boolean)``
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Is the flash ready to strobe? Xenon flashes require their capacitors
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charged before strobing. LED flashes often require a cooldown period
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after strobe during which another strobe will not be possible. This
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is a read-only control.
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