| The cafe_ccic driver |
| ==================== |
| |
| Author: Jonathan Corbet <corbet@lwn.net> |
| |
| Introduction |
| ------------ |
| |
| "cafe_ccic" is a driver for the Marvell 88ALP01 "cafe" CMOS camera |
| controller. This is the controller found in first-generation OLPC systems, |
| and this driver was written with support from the OLPC project. |
| |
| Current status: the core driver works. It can generate data in YUV422, |
| RGB565, and RGB444 formats. (Anybody looking at the code will see RGB32 as |
| well, but that is a debugging aid which will be removed shortly). VGA and |
| QVGA modes work; CIF is there but the colors remain funky. Only the OV7670 |
| sensor is known to work with this controller at this time. |
| |
| To try it out: either of these commands will work: |
| |
| .. code-block:: none |
| |
| $ mplayer tv:// -tv driver=v4l2:width=640:height=480 -nosound |
| $ mplayer tv:// -tv driver=v4l2:width=640:height=480:outfmt=bgr16 -nosound |
| |
| The "xawtv" utility also works; gqcam does not, for unknown reasons. |
| |
| Load time options |
| ----------------- |
| |
| There are a few load-time options, most of which can be changed after |
| loading via sysfs as well: |
| |
| - alloc_bufs_at_load: Normally, the driver will not allocate any DMA |
| buffers until the time comes to transfer data. If this option is set, |
| then worst-case-sized buffers will be allocated at module load time. |
| This option nails down the memory for the life of the module, but |
| perhaps decreases the chances of an allocation failure later on. |
| |
| - dma_buf_size: The size of DMA buffers to allocate. Note that this |
| option is only consulted for load-time allocation; when buffers are |
| allocated at run time, they will be sized appropriately for the current |
| camera settings. |
| |
| - n_dma_bufs: The controller can cycle through either two or three DMA |
| buffers. Normally, the driver tries to use three buffers; on faster |
| systems, however, it will work well with only two. |
| |
| - min_buffers: The minimum number of streaming I/O buffers that the driver |
| will consent to work with. Default is one, but, on slower systems, |
| better behavior with mplayer can be achieved by setting to a higher |
| value (like six). |
| |
| - max_buffers: The maximum number of streaming I/O buffers; default is |
| ten. That number was carefully picked out of a hat and should not be |
| assumed to actually mean much of anything. |
| |
| - flip: If this boolean parameter is set, the sensor will be instructed to |
| invert the video image. Whether it makes sense is determined by how |
| your particular camera is mounted. |
