Transmeta's Crusoe: How it works

The chip relies on software smarts to save power while keeping performance high

Transmeta is billing its Crusoe chip as the first smart, software-upgradable microprocessor.

The company Wednesday unveiled its new family of software-based processors for Internet appliances and mobile notebook PCs. Transmeta officials believe that for a number of reasons Crusoe is the key to opening the gates of the mobile Internet computing revolution. "Crusoe products will span a complete range of mobile computers," said David Ditzel, president and CEO of Transmeta. "What we say at Transmeta is if it has a battery and a browser, it's going to be Transmeta."

Those grand plans are backed up by what the company says is a brand new approach to microprocessor design. Instead of increasing performance through hardware design, such as increasing the number of transistors, Crusoe chips complete three-quarters of their processing in software.

Using a software element called Code-Morphing Software by Transmeta, Crusoe chips transform instructions meant for other processor types, namely x86 chips manufactured by Intel or Advanced Micro Devices (AMD), to instructions that can be run by one of its own TM3120 of TM5400 processors. This means that the chips can run the Windows operating system and Windows applications on top of or in place of Transmeta's own Mobile Linux.

This approach is a departure from traditional chip design, but an intentional one.

Code morphing software "changes the X86 instructions into VLIW (very long instruction word) instructions", said Doug Laird, vice president of product development at Transmeta. "As a result you (can build) a very simple, fast processor."

The Crusoe design, using a VLIW architecture, can handle, for example, 128-bit wide instruction sets, where Intel chips are limited to 32-bit wide sets.

The new Crusoe TM3120 and TM5400 chips are aimed at Internet appliances and notebook PCs, respectively. They serve to run VLIW versions of X86 processors created by code-morphing software.

But why go to all the trouble? Transmeta says the benefits to consumers given by this approach are many. "We are only at the beginning of optimisation of the code-morphing software. New software releases can add performance independently (of hardware updates)," Ditzel said.

Code-morphing software makes Crusoe "smart", according to the company. That is because as it translates instructions, the chip analyses how a someone uses a particular program. With that information, the chip can optimise instructions. For example, it can improve performance by eliminating redundant instructions.

The benefits of doing it in software include tremendous increases in battery life and lower cost as a result of having a simpler processor design. Crusoe chips, for example, have many fewer transistors than an Intel Pentium III. This allows them to run comparatively cooler, eliminating the need for a fan, which adds cost and consumes power.

The two Crusoe processors, for example, average about one watt of power consumption. Prompted by power-management software, called LongRun, the chips can scale between a number of clock frequencies, consuming more or less power as needed by an application. LongRun acts as a dimmer would with a light bulb, allowing only enough light to see, but not too much. That means if only 400MHz is needed to run an application, the chip will run at 400MHz and consume about 1.4 watts of power.

When it comes to Internet appliances, the Crusoe 3120 chip will be optimised to work with Transmeta's Mobile Linux. This operating system will be used along with 3120 in a number of devices demonstrated by Transmeta.

One device demonstrated was a wireless personal access appliance that will let consumers use the device as they would use a wireless phone, roaming around a house, surfing the Web from anywhere in the house. This kind of device will be priced between about $500 (£305) and $999.

"We're not really focusing on the cell phone or the Palm Pilot space," said Jim Chapman, Transmeta's vice president of sales and marketing.

The company will also target sub-4-pound notebook PCs with the 5400 chip, due mid-year. The chip scales between 500MHz and 700MHz and plugs directly into the traditional PC architecture, supporting things such as a PCI bus and synchronous dynamic RAM. The chip also has support for double data rate SDRAM. "End users are calling on (PC makers) for lighter-weight form factors, and of course they like to have better battery life," Chapman said.

Transmeta will have a number of partners, although the company did not reveal any names. The only hint given was that Transmeta is working with a Japanese notebook maker.

IBM will build the Crusoe chips in its Burlington, Vermont fabrication plant.

Read news comment about Transmeta and the Crusoe chip at AnchorDesk.

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