Kontron COMe-bHL6 - Manual (Page 50)

COMe-bHL6 / Features and Interfaces
4.14 Dynamic FSB Frequency Switching
Dynamic FSB frequency switching effectively reduces the internal bus clock frequency by half to further decrease the
minimum processor operating frequency from the Enhanced Intel SpeedStep Technology performance states and achieve
the Super Low Frequency Mode (Super LFM). This feature is supported at FSB frequencies of 1066 MHz, 800 MHz and 667
MHz and does not entail a change in the external bus signal (BCLK) frequency. Instead, both the processor and GMCH
internally lower their BCLK reference frequency to 50% of the externally visible frequency. Both the processor and GMCH
maintain a virtual BCLK signal (VBCLK) that is aligned to the external BCLK but at half the frequency.
After a downward shift, it would appear externally as if the bus is running with a 133-MHz base clock in all aspects, except
that the actual external BCLK remains at 266 MHz. See Figure 3 for details. The transition into Super LFM, a “down-shift,”
is done following a handshake between the processor and GMCH. A similar handshake is used to indicate an “up-shift,” a
change back to normal operating mode. Please ensure this feature is enabled and supported in the BIOS.
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