CPU

From Free60 Project

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General Information

The Xbox 360 uses a custom IBM PowerPC CPU called, "Xenon". "The basic design is a 64-bit PowerPC architecture, with the complete PowerPC ISA available." (Brown) It is different from the Intel Pentium III in the original Xbox. The "Xenon" CPU is composed of three symmetrical cores.

  • 90 nm process, 165 million transistors
  • 168 mm2 die size; one cpu core is about 28mm2
  • Three symmetrical cores, each one running at 3.2 GHz
    • 64 bit CPU cores based on the IBM 970 "G5" design
    • Two-way symmetric multiprocessing (two hardware threads per core; six total)
    • 128 VMX-128 registers per hardware thread
    • One VMX-128 vector unit per core; three total
    • 32kB L1 cache & 32KB instruction cache per core
  • 1 MiB L2 cache (lockable by the GPU) shared by the 3 cores
  • 21.6 GB/s front side bus (aggregated 10.8 GB/s upstream and downstream)
  • 115 GFLOPS theoretical peak performance
  • CPU Integer Perf (VPR): 1089 (363 each)
  • IBM eFuse technology
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Linux Support

  • We have full SMP support, so we can use all three cores.
  • However, we currently need to disable the secondary threads because of a yet-to-be analyzed stability issue.
  • The CPU is quite slow on general purpose code. Due to the non out-of-order execution core, it heavily relies on the compiler to do proper optimizations. GCC currently doesn't know how to do this, resulting in running but very inefficient code.
  • The Cell people are working on ppu-gcc, from which the Xenon will benefit as well, as the PPC cores is quite similiar to the Cell's PPU.
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External Links

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