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by Kenjiro Cho #07 11/28/2002

alternative clocks

• Pentium TSC (Time Stamp Counter)
  
  
  • high-resolution
    
    
    • a 64bit counter driven by CPU clock
      
      
    • 1nsec resolution for 1GHz CPU
      
      
  • light-weight
    
    
    • one instruction to read counter value
      
      
    • even in user space
      
      
  • drawbacks
    
    
    • frequency varies
      
      
    • power management changes CPU clock
      
      
• external clock source
  
  
  • GPS, shortwave radio, CDMA
    
    
    • serial interface overhead