Window processing in an on screen display system

Abstract

Abstract An On Screen Display (OSD) system for a digital television set-top box is provided. The OSD can simultaneously display different kinds of pictures, (e.g., a bit-map, a graphic, a still video picture, a motion video picture or a background color). Each picture is in a different window that is managed by hardware. An OSD controller changes the display mode in real time during generation of the display. The OSD controller calculates, in real time for each line, the address and the size of each segment of a window that makes up the current line. A display memory is organized by window and located in an SDRAM; the same memory space is used for both the display's frame memory and the CPU's working area. The controller reads the segments from the memory space that contain the full windows created by the CPU. The controller reads the windows, segment by segment, and transfers data to an OSD FIFO during display, overlapped parts not visible are not read. For each pixel, the OSD decoder reads into the FIFO the bits required to display the current pixel. The number of bits per pixel varies during the display depending of the mode. An address calculator, a pixel selector and a controller select the bits of data from the FIFO to form the current pixel.

Inventors

• 👤 Gerard Chauvel

Bibliographic Details