Image Number 4 for United States Patent #RE43235.
A graphics controller for a System-On-a-Chip (SOC) used with a battery-powered device allows for reduced-power display modes. The microprocessor writes to a frame buffer that is a single, contiguous address block in virtual memory. A memory management unit (MMU) translates frame-buffer address to multiple physical blocks. The graphics controller fetches pixels from the multiple physical blocks, including a block in an on-chip memory and a block in an external memory. In a low-power mode, pixels are only fetched from the lower-power on-chip memory and not the higher-power external memory. A smaller display window is defined and pixels outside the window are replaced by dummy data, .eliminating external-memory fetches. The smaller display window falls within the first block in the on-chip memory. Status and other information can be displayed in the smaller display window during stand-by modes, while a full-screen of data is displayed for full-power modes.