DISPLAY ROTATION USING A SMALL LINE BUFFER AND OPTIMIZED MEMORY ACCESS

A frame buffer stores X pixels per line and Y lines and is read using a burst of B pixels. The un-rotated image is rotated by 90 degrees for display by writing and reading pixels from a line buffer. The line buffer stores a block of B*Y pixels. The frame buffer is logically divided into X/B blocks that are B pixels wide. Blocks are read from the frame buffer from the bottom line to the top with a burst of B pixels per line. An offset locate pixels to read in the line buffer. The offset is B for the first block, and increases by a factor of B for each block read, but wraps around modulo B*Y−1. Pixels for a next block are written into the line buffer to locations vacated as pixels are read out. The increasing offset re-orders the pixels for the rotated display order.