Processor vendors hope to get an "arm up" on the competition

-- EDN, 11/23/2000

If the expression "imitation is the sincerest form of flattery" is true, then ARM Ltd should be feeling good. All the company's challengers, including Lexra and TI, seem to want to do lately is talk about how their products stack up against ARM's latest cores and ARM partners' processors (Picture). Take Lexra, for example. The company's LX5180 documentation is full of comparisons to ARM's 9E core: power, performance, cost, and ease of design integration.

The LX5180 is a lower cost, lower power variant of the earlier LX5280. Whereas the LX5280 is a dual-issue, superscalar architecture with one "engine" a control processor and the other a DSP, the LX5180 adopts a single-issue, scalar, merged control-plus-DSP approach. LX5xxx series processors incorporate a six-stage pipeline, whereas previous-generation LX4180 and LX4280 architectures used a five-stage pipeline. Also, the LX51280 contains optional single-pipeline-stage-fed, 16- or 32-bit dual hardware MAC (multiply-accumulator) units versus the LX5280's dual-pipeline-stage MAC units. Lexra provides the LX5180 in fully synthesizable Verilog that, on a 0.18-µm process, the company estimates can achieve speeds as high as 180 MHz at 1.8V. Price is a customer-specific combination of $425,000 license and per-unit royalty fees ($1 at a 500,000-unit run rate, for example).

Now for Texas Instruments. Whereas Lexra's latest chip is a variant of the previous generation with fewer features, TI's DA250 is the company's first audio-targeted DSP based on the dual-MAC-unit c55xx core. The DA250 also offers finer grained peripheral-power control than previous c54xx-based devices. The initial version of the DA250, built on a 0.15-µm-process version, runs at 160 MHz at 1.5V, translating to a DSP performance of 320 MIPS. At 1.1V, the DA250 will achieve 100-MHz, 200-MIPS performance. TI predicts that the subsequent 0.135-µm-process version of the DA250, which will become available in the second half of next year, will hit 200-MHz, 400-MIPS speeds at 1.5V. DA250 embeds 128k words of RAM and 32k words of ROM.

The first three DAxxx devices were pinout-compatible with each other, although core voltages scaled downward from one generation to the next. The DA250 breaks that mold, because of its integrated USB 1.1 controller; multiformat mass-storage and other peripheral interfaces; and its increased number of general-purpose, 2.25 to 3.6V I/O pins. Previously developed software is upwardly compatible with the DA250; however, the company recommends that users recompile their code to take advantage of the dual MAC units. The DA250 comes in 144-pin TQFP and 179-bump µBGA packages, will be available for sampling in January 2001, and will cost less than $10 (250,000). TI also plans a $1000 prototyping board, which includes evaluation licenses to many of the audio codecs that the chip supports; MP3 for decoding and encoding, WMA, ATRAC3, ePAC, AAC, TwinVQ, RealAudio, and various media-watermarking and security protocols.

Both of ARM's competitors feel they're offering customers more robust digital-signal-processing capability-with higher performance, lower power, or both-translating to reduced energy draw to implement functions such as matrix arithmetic. Lexra, for example, claims that a 64-sample dot product will, at 180 MHz, take 600 nsec on its LX5180 versus 1800 nsec on the ARM9E. ARM's upcoming SIMD (single-instruction-multiple-data) instruction-set additions, the successor to the company's not widely used Piccolo architecture, may neutralize any short-term advantage for Lexra and other ARM competitors, though. ARM announced its SIMD approach at October's Microprocessor Forum.

ARM Ltd, 1-408-579-2200, www.arm.com. at www.rscahners.ims.ca/ednmag/.

Lexra, 1-408-573-1890, www.lexra.com. at www.rscahners.ims.ca/ednmag/.

Texas Instruments, 1-972-995-2011, www.ti.com. at www.rscahners.ims.ca/ednmag/.

-by Brian Dipert