Electronic Design

Cost-Savvy DSP Chip Trio Keeps Performance High

Second generation of Blackfin low-power processors targets converging multimedia and communications.

Today's rapid convergence of the multimedia and communications markets is forcing designers to respin processors to meet the low-cost, high-performance, and low-power demands of products designed for consumer applications.

Products like cell phones, PDAs, and tablet PCs need to execute a wide range of algorithms that handle video, still images, voice, music, and other media. Most of these consumer products include a general-purpose RISC processor that can handle the bulk of the algorithms. Yet increasing algorithm complexity leaves little processor performance for other aspects of system operation. Cost sensitivity, though, usually dictates that only a low-cost dedicated solution can deliver a viable solution. Similarly, generic DSP chips could easily be overloaded by the media-processing tasks, as many algorithms require hundreds of MIPS for real-time execution.

From these often contradictory requirements, Analog Devices has developed a second-generation Blackfin processor family that meets the cost and performance needs of these demanding applications. Available now in lots of 10,000, the new Blackfin processors cost as little as $4.95 each. But the low cost won't hinder performance—the ADSP-BF531 operates at 300 MHz and delivers 600 million multiply-accumulates (MACs) per second. A higher 400-MHz clock-speed version delivers 800 million MACs. Even higher-performance models, the ADSP-BF532 and BF533, offer top compute throughputs of 800 million and 1200 million MACs.

But raw throughput is just the start for the new Blackfin processors, as they perform at extremely low power levels as well. The BF533 consumes just 280 mW at 600 MHz. At lower clock speeds, power drops dramatically. The chip consumes just 90 mW at 300 MHz, while at 200 MHz power drops to a mere 52 mW. In other words, the Blackfin processors deliver double the performance of competitive products running at the same power levels.

To keep power low, designers took two approaches. First, an on-chip regulator takes the external 2.25- to 3.6-V input and regulates it down to 0.7 to 1.2 V (programmable in 50-mV increments). Second, they incorporated dynamic power-management capability that can intelligently adjust clock speeds and core voltage levels to minimize the power for the task currently executing (Fig. 1).

At the heart of the Blackfin processors lies a dual-MAC core that efficiently processes multiple telephony and digital audio algorithms (Fig. 2). Each MAC consists of a 16-bit multiplier and a 40-bit accumulator. In addition, a quartet of video ALUs and a barrel shifter allow the core to execute four 8-bit math operations per cycle. This considerably reduces the time needed to execute an 8- by 8-bit discrete cosine transform or motion-estimation algorithm. Such computations are key elements of mainstream multimedia standards, like MPEG video compression or JPEG imaging.

When running at 600 MHz, the BF533 consumes just less than half of its throughput to implement an MPEG-2 player that delivers D1 quality (720 by 480 pixels) at 30 frames/s. An MPEG-4 player takes about 52% of the chip's loading. An MP3 player consumes just 8% of the chip's processing resources, while a WMA (Windows media audio) player (pro version 9) demands about 21% of the compute resources. Speech-processing applications, such as codecs for G.768, 726, and 729, each consume under 4.5% of the compute resources, while a DTMF function requires a mere 0.3% of the compute capabilities.

On-chip multimedia support starts with a dozen DMA channels that let the processors handle both one- or two-dimensional data transfers. A pair of dual-channel, full-duplex synchronous serial ports support eight stereo I2S channels, and a parallel peripheral interface supports the ITU-R 656 video data format.

To tackle the complex algorithms, the BF531 packs 52 kbytes of on-chip RAM, the BF532 offers 84 kbytes, and the BF533 jumps up to 148 kbytes. The BF531 and 532 also contain 32 kbytes of on-chip, user-definable ROM. All three chips feature a memory controller that provides a glueless interface to multiple banks of SDRAM, SRAM, flash memory, or ROM. Additional resources include a trio of counter-timers that offer pulse-width modulation, pulse-width and event counting modes, a universal asynchronous receiver-transmitter (UART) with support for an infrared data interface, a serial-peripheral-interface-compatible serial port, a real-time clock, and a watchdog timer.

With their parallel peripheral interface, the chips can connect to a variety of video encoders/decoders, display drivers, and general-purpose converters. Bit-definable I/O pins are individually programmable as general-purpose I/O lines or as elements of a parallel datapath. In the video mode, the port supports the decoding of embedded ITU-R 656 preamble information packets as a synchronization mechanism. Thus, the port provides a glueless interface between the Blackfin processors and an external ITU-R 656-enabled device.

The two main serial ports are tuned specifically for use in high-end consumer audio applications. Each serial port has two transmit and receive channels available, and all channels support the I2S format. As a result, the Blackfin chips can process up to eight stereo I2S channels. The serial ports also pack additional functionality for telecommunications applications. Every port handles a programmable window of 128 time-division multiplexing channels out of a 1024-channel bank. Furthermore, the ports support up to 32-bit word widths at data rates of up to 100 Mbits/s.

To develop software for the Blackfin processors, ADI crafted the Crosscore suite of development tools. Included in the suite is the VisualDSP++ software development environment, the EZ-KIT Lite evaluation systems, and emulators.

Initially, the second-generation Blackfin family will consist of the ADSP-BF531, BF532, and BF533. In lots of 10,000 units, the DSP chips cost as little as $4.95 for the 300-MHz BF531 and as much as $19.95 for the 600-MHz BF533. The BF531 and BF532 come in either a 176-lead quad flat package or a 160-contact mini-BGA. The BF533 is offered only in the 160-contact mini-BGA. All three processors are immediately available.

(781) 329-4700 www.analog.com

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