VLIW: Very Long Instruction Word

Transmeta Crusoe

Transmeta Crusoe TM3120

The Code Morphing technology does a fair bit of its own caching. When a new segment of instructions is processed, it is first decoded bit-by-bit, and assigned to native VLIW instructions. When the Code Morphing software starts to see these strings repeating, it optimizes the routines (in large chunks) into very efficient VLIW code, stored in a special translation cache for fast access. The software goes one step farther, though -- it actively watches what goes on in the cache. If a particular block from the translation cache is being accessed frequently, the software goes back to it and continues to re-optimize it, such that it continues to get faster and faster. It also monitors the branches that are most often taken, and will refine its prediction algorithm accordingly.

It is also worth noting that the Code Morphing software is stored on a 1MB flash ROM chip and is loaded into SDRAM when the chip starts up. Moreover, the software was designed to be scalable to any non-x86 architecture. This means that Transmeta is free to upgrade the chip's base-level software as needed.

Crusoe core diagram (from Transmeta)
Crusoe's CPU.
(diagram from Transmeta)

The combination of Crusoe's extensive software layer and its small hardware footprint means that it runs at extremely low power. The flagship TM5800 chip operates between 0.8 to 1.3V, and consumes at most 1.5 W during high-workload applications (e.g., DVD playback). Comparatively, Intel's Celeron processor operates at up to 27.5 W. Similar AMD chips operate near 34 W.

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