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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: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
This commit is contained in:
Robert Jarzmik 2009-04-24 12:58:35 -03:00 committed by Mauro Carvalho Chehab
parent c09b77806e
commit 5660009364
1 changed files with 49 additions and 0 deletions
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49
Documentation/video4linux/pxa_camera.txt
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@ -26,6 +26,55 @@ Global video workflow
Once the last buffer is filled in, the QCI interface stops. 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 DMA usage
--------- ---------