The two chips are nearly identical. Both are based on an ARM1136JF-S core running at up to 665 MHz. This core includes ARM’s “Vector Floating Point” coprocessor. Both chips also offer a MPEG-4 encode/decode coprocessor, an “image processing unit,” and a wealth of memory and peripherals. The only difference between the processors is that the i.MX31 includes a 2D/3D graphics coprocessor, but the i.MX31L does not.

All of this hardware gives the new chips an impressive amount of processing power. BDTI recently analyzed the signal-processing performance of the ARM1136 core that is at the heart of these processors. Based on results of the BDTI Benchmarks™, a 665 MHz ARM1136 offers substantial signal-processing speed. For example, it is about roughly 60% faster than Texas Instruments’ 300 MHz ‘C55x. (See http://www.BDTI.com/bdtimark/BDTImark2000.htm for benchmark scores.)

The capabilities of the video hardware are also notable. The MPEG-4 coprocessor supports simultaneous encoding and decoding at VGA resolution at 30 frames per second with minimal loading on the ARM1136. Similarly, the image processing unit offloads rotation, resizing, and other common video- and image-processing tasks from the ARM1136. A key drawback to this hardware is that it offers limited flexibility. In particular, the MPEG-4 coprocessor cannot be used for other video compression algorithms such as WMV9.

The various coprocessors should help the i.MX31 and i.MX31L achieve good energy efficiency on some graphics, imaging, and video tasks. The i.MX31 and i.MX31L also have several energy-conserving features that are useful for a broad range of tasks. The chips offer many commonplace energy-conserving features such as low-power modes, as well as less common features such as back biasing (a circuit technique that reduces standby power). The chips are also able to vary their frequency and voltage automatically based on processor loading. The ability to operate over a range of frequencies and voltages is fairly rare. Chips that do offer this feature usually control frequency and voltage through software. This software control involves communication between the operating system, the application tasks, and the frequency/voltage control hardware—potentially a complicated process. With the i.MX31 and i.MX31L, the chip itself monitors the processor loading. According to Freescale, this enables the chips to automatically select the appropriate frequency and voltage.

The Freescale chips also offer dynamic process and temperature compensation. With most embedded processors, the operating voltage is set with a significant margin of safety. As a result, these chips usually operate higher-than-needed voltages. In contrast, the Freescale chips include circuitry that determines the voltage needed for the current conditions. This feature works in conjunction with the dynamic voltage scaling feature to ensure that the chip is always operating at the minimum voltage required for the current conditions.

The i.MX31 and i.MX31 offer a number of impressive features. However, Freescale has not yet disclosed power consumption or pricing data for these chips. Without this data, it is impossible to tell how competitive these parts will be. Currently, Freescale is only sampling the chips to selected customers. BDTI hopes that Freescale will release additional data when the chips become more widely available.