Merge pull request #823 from luxonis/3a_fps_limit

Added 3A FPS limiting to debugging docs (debugging CPU usage)

Author: Erol444

docs/source/tutorials/debugging.rst

@@ -121,4 +121,45 @@ specifically SHAVE core and CMX memory usage:
 
 In total, this pipeline consumes 15 SHAVE cores and 16 CMX slices. The pipeline is running an object detection model compiled for 6 SHAVE cores.
 
+CPU usage
+=========
+
+When setting the :ref:`DepthAI debugging level` to debug (or lower), depthai will also print our CPU usage for LeonOS and LeonRT. CPU usage
+at 100% (or close to it) can cause many undesirable effects, such as higher frame latency, lower FPS, and in some cases even firmware crash.
+
+Compared to OAK USB cameras, OAK PoE cameras will have increased CPU consumption, as the networking stack is running on the LeonOS core. Besides
+reducing pipeline (doing less processing), a good alternative is to reduce 3A FPS (ISP). This means that 3A algorithms (auto exposure, auto white balance
+and auto focus) won't be run every frame, but every N frames. When updating DepthAI SDK's `camera_preview.py <https://github.com/luxonis/depthai/blob/main/depthai_sdk/examples/CameraComponent/camera_preview.py>`__
+example (code change below), the LeonOS CPU usage decreased from 100% to ~46%:
+
+.. code-block:: bash
+
+    # Without 3A FPS limit on OAK PoE camera:
+    Cpu Usage - LeonOS 99.99%, LeonRT: 6.91%
+
+    # Limiting 3A to 15 FPS on OAK PoE camera:
+    Cpu Usage - LeonOS 46.24%, LeonRT: 3.90%
+
+Not having 100% CPU usage also drastically decreased frame latency, in the example for the script below it went from ~710 ms to ~110ms:
+
+.. image:: https://github.com/luxonis/depthai-python/assets/18037362/84ec8de8-58ce-49c7-b882-048141d284e0
+
+.. code-block:: diff
+
+    from depthai_sdk import OakCamera
+
+    with OakCamera() as oak:
+        color = oak.create_camera('color')
+        left = oak.create_camera('left')
+        right = oak.create_camera('right')
+
+  +     # Limiting 3A to 15 FPS
+  +     for node in [color.node, left.node, right.node]:
+  +         node.setIsp3aFps(15)
+
+        oak.visualize([color, left, right], fps=True, scale=2/3)
+        oak.start(blocking=True)
+
+Limiting 3A FPS can be achieved by calling :code:`setIsp3aFps()` function on the camera node (either :ref:`ColorCamera` or :ref:`MonoCamera`).
+
 .. include::  /includes/footer-short.rst

docs/source/tutorials/low-latency.rst

@@ -125,7 +125,7 @@ On PoE, the latency can vary quite a bit due to a number of factors:
   * Network/computer is saturated with other traffic. You can test the actual bandwidth with `OAK bandwidth test <https://github.com/luxonis/depthai-experiments/tree/master/random-scripts#oak-bandwidth-test>`__ script. With direct link I got ~800mbps downlink and ~210mbps uplink.
 
 * Computer's **Network Interface Card settings**, `documentation here <https://docs.luxonis.com/projects/hardware/en/latest/pages/guides/getting-started-with-poe.html#network-interface-controller-settings>`__
-* 100% OAK Leon CSS (CPU) usage. The Leon CSS core handles the POE communication (`see docs here <https://docs.luxonis.com/projects/hardware/en/latest/pages/rvc/rvc2.html#hardware-blocks-and-accelerators>`__), and if the CPU is 100% used, it will not be able to handle the communication as fast as it should.
+* 100% OAK Leon CSS (CPU) usage. The Leon CSS core handles the POE communication (`see docs here <https://docs.luxonis.com/projects/hardware/en/latest/pages/rvc/rvc2.html#hardware-blocks-and-accelerators>`__), and if the CPU is 100% used, it will not be able to handle the communication as fast as it should. **Workaround:** See :ref:`CPU usage` docs.
 * Another potential way to improve PoE latency would be to fine-tune network settings, like MTU, TCP window size, etc. (see `here <https://docs.luxonis.com/projects/hardware/en/latest/pages/guides/getting-started-with-poe.html#advance-network-settings>`__ for more info)
 
 Bandwidth