SPRUIL1D May 2019 – December 2024 DRA829J , DRA829J-Q1 , DRA829V , DRA829V-Q1 , TDA4VM , TDA4VM-Q1
The write-back (WB) pipeline is used to store in the system memory the capture of the overlay output or the output of one of the pipelines. The WB pipeline consists of a CSC unit, a scaler unit, and an RGB truncation logic. The format from the overlay managers is always ARGB48. The format from the output of the VID pipeline can be YUV422, YUV420 or ARGB48. Because the overlay works on ARGB48 format and the video accelerator works on YUV format, the color space conversion from RGB to YUV is used to directly output to memory the format that can be encoded with no extra processing.
The write-back pipeline can be connected either to the VID pipeline output or to the output of one of the overlay managers, either in M2M (memory-to-memory) or Capture mode (see Section 12.6.4.6.3, DISPC Write DMA Buffer), by configuring the DSS0_COMMON_DISPC_CONNECTIONS[20-16] WB_CONN register field.
The capture frame rate can be set in the DSS0_WB_ATTRIBUTES[26:24] CAPTUREMODE bit field.
The write-back pipeline also supports input source cropping to allow a sub-frame capture.
The ARGB48 format is truncated (LSB drop) or expanded to match the output color depth formats. No dithering on the output is supported. When there is no alpha field mentioned by x in the pixel format description, 0's shall be used. For example, for RGB12 pixel format the upper 4 bits are 0’s since RGB value is only 12 bits inside a 16-bit container.
The WB pipeline is enabled by setting the DSS0_WB_ATTRIBUTES[0] ENABLE bit to 0x1.
Figure 12-585 shows the WB pipeline.