SPRUIE9D May 2017 – May 2024 DRA74P , DRA75P , DRA76P , DRA77P
The Write DMA block can convert data in YUV422 format into YUV422BP format. The BP refers to "Bi-Planer", where Y and UV are split out onto two separate DMA channels (CAL does not perform the decimation). The format conversion to YUV422BP, when enabled, takes place after the cropping stage.
SW must program two adjacent Write DMA contexts for the YUV422BP conversion. The Y channel is always an even numbered context, while the UV channel is the next context (that is, Y is context #0 and UV is context #1). The Y context is the dominant and the UV is the slave. The YUV422BP register bits are set for both channels/contexts. Both Write DMA channels shall be programmed identically except for the destination address. Even the CAL_WR_DMA_CTRL_k[2:0] MODE register bit-field should be programmed identically for both channels. Internally, the slave channel will be disabled from capturing data from its programmed context and will rather accept the UV portion of the data from the dominant channel.
Only YUV422 data format can be converted to YUV422BP and it is the SW responsibility to program upstream modules of CAL to supply YUV422 data for conversion. True YUV420 format would decimate every other line of UV extracted from the YUV422, but CAL does not perform this aspect of the operation .
Internally, the YUV422BP conversion is using pairs of YUV422 bus transactions and separating out Y and UV portions. It then re-inserts these reformed data phases on the internal bus to the Write DMA assigning context n to the Y data and context n+1 to the UV data. The Write DMA treats these Y and UV data streams as two independent contexts. Up stream of the YUV422BP conversion, the CAL treats it as a single context.
Figure 10-34 CAL YUV422 to YUV422BP Conversion (Internal Bus Format)The DMA module extracts the two different contexts from the internal bus to the Write DMA module. As it does with other formats, it packs the data into a buffer per DMA context and writes this out onto the OCP bus once sufficient data is available for an efficient DMA burst.
The following DMA limitations apply to the YUV422BP conversion: