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EPPI misses every second frame?

Question asked by on Aug 14, 2012
Latest reply on Aug 15, 2012 by



I'm using the EPPI of the BF548 with uclinux to grab a video stream from a CMOS imager directly accessing the PPI (no drivers in between).


What I don't understand right now is why my EPPI misses every second frame of the video stream - the sensor pushes them out at 100fps (line-sync) but i just get the transfer-completed interrupts @50Hz.

For the software I'm using the PPI in 2-sync mode, 8bit-width, packing enabled.

the DMA operates with a descriptor link-list, storing the images in different frame buffers in a mmaped region in the external RAM.


Here's my completed config:

// DMA

#define image_height    360

#define image_width             240


#define PPI_CONTROL             XFR_TYPE | 0x20 | DLEN_8 | PACKEN

#define DMA_CONFIG              DMAFLOW_LARGE | NDSIZE_9 | WNR | WDSIZE_32 | DMA2D | DI_EN


#define PPI_FRAME               image_width

#define PPI_LINE                image_height

#define DMA_X_CNT       image_height/2

#define DMA_Y_CNT       image_width

#define DMA_X_MOD       4

#define DMA_Y_MOD       4


A little bit confusing is that the EPPI status register usually signals a 0x4 => Line Track Overflow error. Could that lead to my frameloss?


I actually have no real idea in which direction to debug to - I've checked the config multiple times now. Do you have an idea what could be wrong?


Thanks for your help,