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Commit 56600093 authored by Robert Jarzmik's avatar Robert Jarzmik Committed by Mauro Carvalho Chehab
Browse files

V4L/DVB (11613): pxa_camera: Documentation of the FSM 



After DMA redesign, the pxa_camera dynamic behaviour should
be documented so that future contributors understand how it
works, and improve it.

Signed-off-by: default avatarRobert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: default avatarGuennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@redhat.com>
parent c09b7780

Documentation/video4linux/pxa_camera.txt

+49 −0
Original line number Diff line number Diff line
@@ -26,6 +26,55 @@ Global video workflow 


     Once the last buffer is filled in, the QCI interface stops.



  c) Capture global finite state machine schema



      +----+                             +---+  +----+

      | DQ |                             | Q |  | DQ |

      |    v                             |   v  |    v

    +-----------+                     +------------------------+

    |   STOP    |                     | Wait for capture start |

    +-----------+         Q           +------------------------+

+-> | QCI: stop | ------------------> | QCI: run               | <------------+

|   | DMA: stop |                     | DMA: stop              |              |

|   +-----------+             +-----> +------------------------+              |

|                            /                            |                   |

|                           /             +---+  +----+   |                   |

|capture list empty        /              | Q |  | DQ |   | QCI Irq EOF       |

|                         /               |   v  |    v   v                   |

|   +--------------------+             +----------------------+               |

|   | DMA hotlink missed |             |    Capture running   |               |

|   +--------------------+             +----------------------+               |

|   | QCI: run           |     +-----> | QCI: run             | <-+           |

|   | DMA: stop          |    /        | DMA: run             |   |           |

|   +--------------------+   /         +----------------------+   | Other     |

|     ^                     /DMA still            |               | channels  |

|     | capture list       /  running             | DMA Irq End   | not       |

|     | not empty         /                       |               | finished  |

|     |                  /                        v               | yet       |

|   +----------------------+           +----------------------+   |           |

|   |  Videobuf released   |           |  Channel completed   |   |           |

|   +----------------------+           +----------------------+   |           |

+-- | QCI: run             |           | QCI: run             | --+           |

    | DMA: run             |           | DMA: run             |               |

    +----------------------+           +----------------------+               |

               ^                      /           |                           |

               |          no overrun /            | overrun                   |

               |                    /             v                           |

    +--------------------+         /   +----------------------+               |

    |  Frame completed   |        /    |     Frame overran    |               |

    +--------------------+ <-----+     +----------------------+ restart frame |

    | QCI: run           |             | QCI: stop            | --------------+

    | DMA: run           |             | DMA: stop            |

    +--------------------+             +----------------------+



    Legend: - each box is a FSM state

            - each arrow is the condition to transition to another state

            - an arrow with a comment is a mandatory transition (no condition)

            - arrow "Q" means : a buffer was enqueued

            - arrow "DQ" means : a buffer was dequeued

            - "QCI: stop" means the QCI interface is not enabled

            - "DMA: stop" means all 3 DMA channels are stopped

            - "DMA: run" means at least 1 DMA channel is still running



DMA usage

---------