The VLIW based Crusoe chip from Transmeta is marketed primarily as a high-performance, low power processor for mobile applications.  Transmeta’s product literature indicates that the hardware designers of the Crusoe had the following goal in mind.  They designed the chips for minimal space and lowered power consumption.  The emphasis on smaller dies and low power consumption naturally leads to the question of performance.  With reduced capacitors and software taking over for things that were previously done in hardware, is the Crusoe able to keep up with its high-powered competitors?  Although Transmeta also markets the Crusoe for server applications, the mobile market is its primary target.  Transmeta places a premium on battery consumption as a measure of performance.  After all, a portable device is only functional when it is powered. 

The Crusoe chip is designed to increase battery life through two techniques.  The Crusoe chip focuses on an energy efficient design that reduces the power consumption by implementing functionality, previously reserved for hardware, into their Code Morphing software layer.  This is how Transmeta is able to produce these smaller and more energy efficient processors.  Whereas in conventional superscalar x86 architectures where scheduling is done in hardware, the Crusoe does instruction scheduling in software.  This results in a lower transistor count.  Lowered transistor counts also results in cooler running chips as a result of lowered power requirements.  The two following thermal images were taken during DVD playback.  The first image is that of a Pentium III while the other is that of a Crusoe.  The Crusoe runs considerably cooler and is able to run without active cooling.  The lack of a need for a fan further adds to the Crusoe’s reduced overall power consumption.

 

The other technique used by Transmeta to increase battery life is a power management technology that they have termed LongRun Dynamic Power Management.  The LongRun power management is actually a part of the Code Morphing software layer.  LongRun is a software module that resides within the Code Morphing software layer.  In conventional x86 processors, power consumption is regulated by alternating the state of the CPU between on and off states.  It is through varying the on/off ratio that different performance levels are achieved.  This method of power management produces a linear relationship between power consumption and performance.   As the conventional x86 processor lowers its power consumption, its performance is also reduced.  Although the Crusoe is compatible with this power regulation model, the Crusoe also has processor specific techniques that are able to further exploit reducing battery consumption.  The Crusoe architecture uses a technique that is somewhat like processor throttling.  This is done by dynamically managing the frequency (performance) and voltage levels for a given application at runtime.  In essence, the architecture is designed to only output the performance that is needed.  The LongRun power management system is controlled at the software level, but hardware features designed into the architecture provide the actual functionality.  The Crusoe is able to adjust its frequency in 33 MHz steps.  This is used to step up or down the performance dependent upon the workload.  The voltage changes that are done in conjunction with adjusting the frequency are adjustable by 25 mV increments.  In order to fully use the Crusoe’s ability to change its core voltage and frequency based on the workload, the Crusoe is able to change the frequency and voltage 200 times per second.  The difference between conventional x86 processors and the Crusoe in terms of power management is that conventional x86 processors adjust voltage, leading to a linear scale in power reduction, while the Crusoe because it adjusts both the voltage and frequency is able to produce power reductions on a cubic scale.  The following diagrams illustrate this important concept.  The figure below illustrates the conventional x86 linear power profile for power vs. activity level. 

           

The illustration below is the corresponding graph for the Crusoe.  By having the ability to “throttle” the CPU based upon the current workload by altering not only the voltage, but the frequency as well, the Crusoe is able to further improve upon the conventional power management system.

 

            The following figure below is a real world indication as to how all of this performs.  The Crusoe powered laptops are highlighted in green. 

The resulting scores of the benchmark are given in hours and minutes of the battery life.  The BatteryMark score is the time that a notebook’s battery is able to run for while doing different workloads that simulate use by users.

            The Crusoe has been designed to promote better power management while still factoring in performance.  It has focused primarily on reducing power consumption as a result of the mobile market.  With reduced die sizes that run cooler and longer runtimes, the Crusoe is indeed geared for the mobile industry.  Transmeta places a premium on battery consumption and in doing so, has produced a chip that is able to increase battery runtimes for devices such as laptops.  The Crusoe’s efficiency is its strongest asset when directly compared to conventional x86 processors.