In many smart-camera and image-processing boards, developers combine the power of general-purpose-processor (GPP) or DSP-based systems with programmable logic. Now, Stretch (Mountain View, CA, USA; www.stretchinc.com) has combined the two approaches in a single family of devices known as the S5000 series. By embedding programmable logic inside a software-programmable processor, system designers can extend the processor instruction set itself, not just add complementary external logic nearby. Combining software programmability and programmable logic by embedding the logic inside the processor architecture allows logic to be programmed with conventional software.
The Stretch S5000 software-configurable processors are based on the Stretch S5 engine, which incorporates the Xtensa V RISC processor core from Tensilica (Santa Clara, CA, USA; www.tensilica.com) and Stretch Instruction Set Extension Fabric (ISEF). The ISEF is a software-configurable datapath based on proprietary programmable logic. The FPGA-like ISEF logic is designed for implementing variable-sized ALUs, multipliers, and shifters as datapath extensions to the processor. The ISEF computes complex functions in parallel similar to an FPGA but that can be tailored by system designers for compute-intensive applications.
Using the ISEF, system designers extend the processor instruction set and define the new instructions using C/C++ code. Since the ISEF is reloadable during operation, a small ISEF area can support a number of instructions resulting in greater efficiency than an FPGA-based design. Stretch has shown that the S5000 processors can exceed the performance of GPPs, DSPs, ASPs, and FPGAs.
According to company benchmarks, a 300-MHz Stretch S5610 processor tailored for DSP outperforms all other processors including the 2-GHz FastMATH processor from Intrinsity (Austin, TX, USA; www.intrinsity.com), the 720-MHz C64 processor from Texas Instruments (Dallas, TX, USA; www.ti.com), and the 1.3-GHz PowerPC with Altivec processor from Motorola (Austin, TX, USA; www.motorola.com).