정의

제안위치

1. The camera’s sensor has been configured and is continually streaming frame lines over the CSI-2 interface to the GPU. 2. The GPU is assembling complete frame buffers from these lines and performing post-processing on these buffers (we’ll go into further detail about this part in the next section). 3. Meanwhile, over on the CPU, myscript.py makes a capture call using picamera. 4. The picamera library in turn uses the MMAL API to enact this request (actually there’s quite a lot of MMAL calls that go on here but for the sake of simplicity we represent all this with a single arrow). 5. The MMAL API sends a message over VCHI requesting a frame capture (again, in reality there’s a lot more activity than a single message). 6. In response, the GPU initiates a DMA(Direct Memory Access) transfer of the next complete frame from its portion of RAM to the CPU’s portion. 7. Finally, the GPU sends a message back over VCHI that the capture is complete. 8. This causes an MMAL thread to fire a callback in the picamera library, which in turn retrieves the frame (in reality, this requires more MMAL and VCHI activity). 9. Finally, picamera calls write on the output object provided by myscript.py.

참고