SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
The write-back 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. Because the overlay works on ARGB32-8888 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 is connected to all the pipeline outputs (GFX, VD1, VID2, and VID3 pipelines) and to the output of the three overlay managers (LCD1, LCD2, LCD3, and TV). The input is selected by setting the DISPC_WB_ATTRIBUTES[18:16] CHANNELIN bit field, and the capture frame rate is set in the DISPC_WB_ATTRIBUTES[26:24] CAPTUREMODE bit field.
Because the output format of the TV overlay manager is ARGB40, the graphics pipeline output is ARGB40, the video pipeline outputs are YUV4:2:2, YUV4:2:0, or ARGB40, and the write-back input is ARGB32, the write-back input does not consider the 2 LSBs of each ARGB component.
The write-back pipeline is enabled by setting the DISPC_WB_ATTRIBUTES[0] ENABLE bit to 0x1.
Figure 11-66 shows the graphics pipeline.