ROS-DMA: A DMA Double Buffering Method for Embedded Image Processing with Resource Optimized Slicing

Image processing on a Digital Signal Processor (DSP) often requires image data to be stored in external memory, because the amount of fast on-chip memory is usually very limited. Processing images in external memory causes significant performance drawbacks. This paper presents a double buffering method using Direct Memory Access (DMA), called Resource Optimized Slicing (ROS-DMA), which is intended to be used instead of a Level 2 (L2) data cache. The idea of ROS-DMA is to transfer image slices into small intermediate buffers of fast internal memory, where the processing can be completed utilizing the full processing power. Use of DMA enables the data transfers and the processing to be accomplished in parallel. The proposed method has the advantage of a modular implementation, making it easy to re-use components for various image processing operations. The sequence of transfers is organized in such a way that use of processor resources is optimized to achieve the shortest possible execution time. ROS-DMA can yield substantially better performance compared to using L2 cache. Furthermore, we expect that with ROS-DMA it will be easier to obtain reliable and tight Worst Case Execution Times (WCETs). Test runs achieved up to six times faster execution with ROS-DMA compared to using the L2 cache on a C6416 DSP from Texas Instruments.