Architecture and C++-programming environment of a highly parallel image signal processor

Abstract

A highly parallel single-chip image signal processor architecture has been derived by analysis of image processing algorithms. Available levels of parallelism and their associated demands on data access, control and complexity of operations were taken into account. The RISC-architecture, called “HiPAR-DSP”, consists of a control unit, 16 parallel ASIMD-controlled datapaths with autonomous addressing and instruction selection capability, a local data cache per data path, a shared memory with matrix type data access and a powerful DMA-unit. The proposed architecture was designed by assessing the results of an analysis of characteristic algorithm properties with respect to their inherent parallelization resources, achievable speed up and implementation costs. This resulted in a proper balance between the degree of parallelism and flexibility, leading to a high performance for a wide field of applications. Additional measures were taken to support an efficient high level programmability of the processor. This was achieved by the concurrent implementation of special architectural features and a C++-programming environment. It consists of an adaptation of the GNU C++-compiler and an optimizing assembler, supporting all levels of concurrence offered by the hardware. While most levels of parallelization are kept invisible to the programmer, data-level parallelism is expressed by the programmer using special new data types added to the standard C/C++-data-types. A sustained performance of about 2.0 Gigaoperations per second is achieved by the 100 MHz clocked processor for numerous image processing algorithms, leading to a processing time e.g. for a normalized correlation of a 512 × 512 image with a 32 × 32 correlation mask of 450 ms. Thus, a performance is achieved with a programmable parallel processor architecture that hitherto required the application of a dedicated integrated circuit.