38.6.10.2 Base Layer with Window Overlay Optimization

When the base layer is combined with at least one active overlay (100% opacity overlay), by default, the whole base layer frame is retrieved from the memory though it is not visible.

To optimize the system bandwidth, the LCDC can be configured to prevent the unuseful data from being fetched from system memory.

The following registers are used to disable an invisible area of the base layer:

  • LCDC_BASECFG5:
    • field DISCXPOS (Discard Area Horizontal Position)
    • field DISCYPOS (Discard Area Vertical Position)
  • LCDC_BASECFG6:
    • field DISCXSIZE (Discard Area Horizontal Size)
    • field DISCYSIZE (Discard Area Vertical Size)
  • LCDC_BASECFG4: bit DISCEN (Discard Area Enable)

Each time the overlay window is resized and/or moved, these configuration registers must be reconfigured according to the new overlay window features.

Figure 38-11. Base Layer Discard Area