From 372698ece3492771bececb6fd5f7dd9f74469518 Mon Sep 17 00:00:00 2001 From: Kieran Bingham <kieran.bingham@ideasonboard.com> Date: Sun, 12 Sep 2021 22:30:17 +0100 Subject: Documentation: IPU3 IPA Design guide The IPU3 IPA implements the basic 3A using the ImgU ISP. Provide an overview document to describe its operations, and provide a block diagram to help visualise how the components are put together to assist any new developers exploring the code. Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com> Reviewed-by: Umang Jain <umang.jain@ideasonboard.com> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Reviewed-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com> --- src/ipa/ipu3/ipu3-ipa-design-guide.rst | 155 +++++++++++++++++++++++++++++++++ 1 file changed, 155 insertions(+) create mode 100644 src/ipa/ipu3/ipu3-ipa-design-guide.rst (limited to 'src/ipa') diff --git a/src/ipa/ipu3/ipu3-ipa-design-guide.rst b/src/ipa/ipu3/ipu3-ipa-design-guide.rst new file mode 100644 index 00000000..89c71108 --- /dev/null +++ b/src/ipa/ipu3/ipu3-ipa-design-guide.rst @@ -0,0 +1,155 @@ +IPU3 IPA Architecture Design and Overview +========================================= + +The IPU3 IPA is built as a modular and extensible framework with an +upper layer to manage the interactions with the pipeline handler, and +the image processing algorithms split to compartmentalise the processing +required for each processing block, making use of the fixed-function +accelerators provided by the ImgU ISP. + +The core IPU3 class is responsible for initialisation and construction +of the algorithm components, processing controls set by the requests +from applications, and managing events from the pipeline handler. + +:: + + ┌───────────────────────────────────────────┐ + │ IPU3 Pipeline Handler │ + │ ┌────────┐ ┌────────┐ ┌────────┐ │ + │ │ │ │ │ │ │ │ + │ │ Sensor ├───►│ CIO2 ├───►│ ImgU ├──► + │ │ │ │ │ │ │ │ + │ └────────┘ └────────┘ └─▲────┬─┘ │ P: Parameter Buffer + │ │P │ │ S: Statistics Buffer + │ │ │S │ + └─┬───┬───┬──────┬────┬────┬────┬─┴────▼─┬──┘ 1: init() + │ │ │ │ ▲ │ ▲ │ ▲ │ ▲ │ 2: configure() + │1 │2 │3 │4│ │4│ │4│ │4│ │5 3: mapBuffers(), start() + ▼ ▼ ▼ ▼ │ ▼ │ ▼ │ ▼ │ ▼ 4: processEvent() + ┌──────────────────┴────┴────┴────┴─────────┐ 5: stop(), unmapBuffers() + │ IPU3 IPA │ + │ ┌───────────────────────┐ │ + │ ┌───────────┐ │ Algorithms │ │ + │ │IPAContext │ │ ┌─────────┐ │ │ + │ │ ┌───────┐ │ │ │ ... │ │ │ + │ │ │ │ │ │ ┌─┴───────┐ │ │ │ + │ │ │ SC │ │ │ │ Tonemap ├─┘ │ │ + │ │ │ │ ◄───► ┌─┴───────┐ │ │ │ + │ │ ├───────┤ │ │ │ AWB ├─┘ │ │ + │ │ │ │ │ │ ┌─┴───────┐ │ │ │ + │ │ │ FC │ │ │ │ AGC ├─┘ │ │ + │ │ │ │ │ │ │ │ │ │ + │ │ └───────┘ │ │ └─────────┘ │ │ + │ └───────────┘ └───────────────────────┘ │ + └───────────────────────────────────────────┘ + SC: IPASessionConfiguration + FC: IPAFrameContext(s) + +The IPA instance is constructed and initialised at the point a Camera is +created by the IPU3 pipeline handler. The initialisation call provides +details about which camera sensor is being used, and the controls that +it has available, along with their default values and ranges. + +Buffers +~~~~~~~ + +The IPA will have Parameter and Statistics buffers shared with it from +the IPU3 Pipeline handler. These buffers will be passed to the IPA using +the ``mapBuffers()`` call before the ``start()`` operation occurs. + +The IPA will map the buffers into CPU-accessible memory, associated with +a buffer ID, and further events for sending or receiving parameter and +statistics buffers will reference the ID to avoid expensive memory +mapping operations, or the passing of file handles during streaming. + +After the ``stop()`` operation occurs, these buffers will be unmapped +when requested by the pipeline handler using the ``unmapBuffers()`` call +and no further access to the buffers is permitted. + +Context +~~~~~~~ + +Algorithm calls will always have the ``IPAContext`` available to them. +This context comprises of two parts: + +- IPA Session Configuration +- IPA Frame Context + +The session configuration structure ``IPASessionConfiguration`` +represents constant parameters determined before streaming commenced +during ``configure()``. + +The IPA Frame Context provides the storage for algorithms for a single +frame operation. + +The ``IPAFrameContext`` structure may be extended to an array, list, or +queue to store historical state for each frame, allowing algorithms to +obtain and reference results of calculations which are deeply pipelined. +This may only be done if an algorithm needs to know the context that was +applied at the frame the statistics were produced for, rather than the +previous or current frame. + +Presently there is a single ``IPAFrameContext`` without historical data, +and the context is maintained and updated through successive processing +operations. + +Operating +~~~~~~~~~ + +There are three main interactions with the algorithms for the IPU3 IPA +to operate when running: + +- configure() +- processEvent(``EventFillParams``) +- processEvent(``EventStatReady``) + +The configuration phase allows the pipeline-handler to inform the IPA of +the current stream configurations, which is then passed into each +algorithm to provide an opportunity to identify and track state of the +hardware, such as image size or ImgU pipeline configurations. + +Pre-frame preparation +~~~~~~~~~~~~~~~~~~~~~ + +When configured, the IPA is notified by the pipeline handler of the +Camera ``start()`` event, after which incoming requests will be queued +for processing, requiring a parameter buffer (``ipu3_uapi_params``) to +be populated for the ImgU. This is given to the IPA through the +``EventFillParams`` event, and then passed directly to each algorithm +through the ``prepare()`` call allowing the ISP configuration to be +updated for the needs of each component that the algorithm is +responsible for. + +The algorithm should set the use flag (``ipu3_uapi_flags``) for any +structure that it modifies, and it should take care to ensure that any +structure set by a use flag is fully initialised to suitable values. + +The parameter buffer is returned to the pipeline handler through the +``ActionParamFilled`` event, and from there queued to the ImgU along +with a raw frame captured with the CIO2. + +Post-frame completion +~~~~~~~~~~~~~~~~~~~~~ + +When the capture of an image is completed, and successfully processed +through the ImgU, the generated statistics buffer +(``ipu3_uapi_stats_3a``) is given to the IPA through the +``EventStatReady`` event. This provides the IPA with an opportunity to +examine the results of the ISP and run the calculations required by each +algorithm on the new data. The algorithms may require context from the +operations of other algorithms, for example, the AWB might choose to use +a scene brightness determined by the AGC. It is important that the +algorithms are ordered to ensure that required results are determined +before they are needed. + +The ordering of the algorithm processing is determined by their +placement in the ``IPU3::algorithms_`` ordered list. + +Sensor Controls +~~~~~~~~~~~~~~~ + +The AutoExposure and AutoGain (AGC) algorithm differs slightly from the +others as it requires operating directly on the sensor, as opposed to +through the ImgU ISP. To support this, there is a dedicated action +`ActionSetSensorControls` to allow the IPA to request controls to be set +on the camera sensor through the pipeline handler. -- cgit v1.2.1