SPRUIE9D May 2017 – May 2024 DRA74P , DRA75P , DRA76P , DRA77P
SW can limit the maximum number of lines (defined in CAL_WR_DMA_CTRL_k[31:18] YSIZE register bit-field) to be written into memory for pixel formats (for which line start/end codes are provided). By default, all received lines are written to memory (when the value of [31:18] YSIZE = 0x0000). This feature is typically used to prevent writes outside of the allocated SDRAM buffer even when CAL and the external data transmitter get out of sync (for example, due to EMI on the link).
It is possible also SW to discard part of the received data for pixel and attribute data (that is, header and control data cannot be discarded). This is performed inside the Write DMA cropping block. The feature is enabled by configuring:
The cropping block discards unwanted data and modifies data TAG to preserve integrity. For example, when pixel data is processed:
Cropping is mainly intended to reduce storage requirements / power consumption when digital zoom is used. No dummy data will be written, if the programmed size is less than what is received.
Cropping may also be used for attribute data. It cannot be used for header data. It is SW responsibility to not use cropping for header data. HW does not perform any additional checks.
The Write DMA accumulates data independently for contexts until an OCP write transaction can be generated. That is the case when enough data is available to generate a full burst or when the end of an image line has been reached.
Data cropping is performed after the DPCM encoder. Therefore, horizontal skipping cannot be used when data is DPCM encoded. Otherwise, it will be not possible to decode the data, unless reference samples have been stored to resume decode.
Cropping must be disabled for JPEG data.