SPRUIE9D May 2017 – May 2024 DRA74P , DRA75P , DRA76P , DRA77P
When the vertical front porch (VFP) period starts after the last horizontal front porch (HFP) of the last line or the external VSYNC is received, the DMA buffers are flushed according to the selected output associated with the pipeline. The DMA engine restarts fetching data from the memory through the L3_MAIN interconnect. Enabling or disabling the DISPC flushes the DMA buffers (except the WB DMA buffers).
Programmable high and low thresholds, independent for each DMA buffer, are used by the DMA engine to start and stop requesting data to the L3_MAIN interconnect.
To avoid underflow at the beginning of a frame and have sufficient encoded pixel data to start some processing, a preloading of the DMA buffer is configurable between a fixed value of bytes or the high threshold value. The preload ensures a minimum number of pixels present in the buffer. When the preload value is reached, the associated channel must start pulling pixels out of the DMA buffer. To enable the preload based on the value entered in the DISPC_GFX_PRELOAD[11:0] PRELOAD or DISPC_VIDp_PRELOAD[11:0] PRELOAD bit field, the DISPC_GFX_ATTRIBUTES[11] BUFPRELOAD bit, or the DISPC_VIDp_ATTRIBUTES[19] BUFPRELOAD bit must be set to 0x0.
When self-refresh mode is selected, meaning the data in the DMA buffers are used for multiple frames, and at the end of each frame, the DMA buffers are not flushed.