An Embedded Stream Processor Core Based on Logarithmic Arithmetic for a Low-Power 3-D Graphics SoC

Abstract

A low-power and high-performance 4-way 32-bit stream processor core is developed for handheld low-power 3-D graphics systems. It contains a floating-point unified matrix, vector, and elementary function unit. By exploiting the logarithmic arithmetic and the proposed adaptive number conversion scheme, a 4-way arithmetic unit achieves a single-cycle throughput for all these operations except for the matrix-vector multiplication that takes 2 cycles per result, which were 4 cycles in conventional way. The processor featured by this functional unit and several proposed architectural schemes including embedded register index calculations, functional unit reconfiguration, and operand forwarding in logarithmic domain achieves 19.1% cycle count reduction for OpenGL transformation and lighting (TnL) operation from the latest work. The proposed stream processor core is integrated into a 3-D graphics SoC as a vertex shader to show its effectiveness. The entire SoC is fabricated into a test chip using 1-poly 6-metal 0.18 mu m CMOS technology. The 17.2 mm(2) chip contains 1.57 M transistors and 29 kB SRAM. The stream processor core takes 9.7 mm(2) and dissipates 86.8 mW at 200 MHz operating frequency. It shows a peak performance of 141 Mvertices/s for geometry transformation (TFM) and achieves 17.5% performance improvement and 44.7% and 39.4% power and area reductions for the TFM from the latest work. For power management of the SoC, the chip is divided into the triple power domains separately controlled by dynamic voltage and frequency scaling (DVFS). With this scheme, it shows 52.4 mW power consumption at 60 fps, 50.5% power reduction from the latest work.