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Abstract

Many signal processing applications require both efficiency and programmability. The complexity of modern media processing, including 3D graphics, image compression, and signal processing, requires tens to hundreds of billions of computations per second.

Description of Stream Processor


To achieve these computation rates, current media processors use special-purpose architectures tailored to one specific application. Such processors require significant design effort and are thus difficult to change as media-processing applications and algorithms evolve. Digital television, surveillance video processing, automated optical inspection, and mobile cameras, camcorders, and 3G cellular handsets have similar needs.

The demand for flexibility in media processing motivates the use of programmable processors. However, very large-scale integration constraints limit the performance of traditional programmable architectures. In modern VLSI technology, computation is relatively cheap - thousands of arithmetic logic units that operate at multi gigahertz rates can fit on a modestly sized 1 cm 2 die. The problem is that delivering instructions and data to those ALUs is prohibitively expensive. For example, only 6.5 percent of the Itanium 2 die is devoted to the 12 integer and two floating-point ALUs and their register files; communication, control, and storage overhead consume the remaining die area. In contrast, the more efficient communication and control structures of a special purpose graphics chip, such as the NVIDIA GeForce4, enable the use of many hundreds of floating-point and integer ALUs to render 3D images.

Conventional signal processing solutions can provide high efficiency or programmability, but are unable to provide both at the same time. In applications that demand efficiency, a hardwired application-specific processor-ASIC (application-specific integrated circuit) or ASSP (application-specific standard part)-has an efficiency of 50 to 500 GOPS/W, but offers little if any flexibility. At the other extreme, microprocessors and DSPs (digital signal processors) are completely programmable but have efficiencies of less than 10 GOPS/W.