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Projects - Clock scaling


Clock and voltage scaling for the SA-1100

Clock scaling allows you to change the clock speed of the running CPU on the fly. This is a nice method to save battery power, because the lower the clock speed, the less power the CPU consumes. Because the clock scaling is integrated in the CPU, all SA-1100 and SA-1110 systems support clock scaling (though it needs some work in the kernel driver).

Voltage scaling is a mean to save even more power, because the lower the clock speed, the lower the CPU core voltage can be. Some LARTs have a little extra hardware to change the CPU core voltage on the fly.

Publications

Johan has written a couple of nice papers about clock and voltage scaling:

  • Voltage scaling on a low-power microprocessor,
    J.A. Pouwelse, K. Langendoen, H. Sips,
    Mobile Computing Conference (MOBICOM), Jul 2001 (accepted for publication)
    (287KB compressed .ps file)
  • Energy priority scheduling for variable voltage processors,
    J.A. Pouwelse, K. Langendoen, H. Sips,
    International Symposium on Low-Power Electronics and Design (ISLPED), Aug 2001 (accepted for publication)
    (48KB compressed .ps file)
  • Power-aware video decoding,
    J.A. Pouwelse, K. Langendoen, R.L. Lagendijk, H. Sips,
    Picture Coding Symposium (PCS), 2001
    (125KB .ps file)
  • Voltage scaling on a low-power microprocessor,
    J.A. Pouwelse, K. Langendoen, H. Sips,
    MMSA, 2000
    (256KB compressed .ps file)

Johan has some other nice papers on his homepage, and also software that implements the userland policy for clock scaling.

Erik did a Cpufreq overview paper at the 2002 Ottawa Linux Symposium.

Who's who

Johan is currently working on the userland policy (and writing his Ph.D. thesis). Erik maintains the SA-1100 driver, Russell King developed the generic framework and maintains SA-1110 support, support for AMD K6-2+/3+, AMD Athlon Powernow, Intel SpeedStep, and VIA/Cyrix C3 is being done by Dave Jones and Arjan van de Ven. Domonik Brodowski did the SpeedStep and ACPI drivers and maintains the cpufreq technical pages.


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