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- The current implementation allows the user to specify the desired CPU
- clock value, in MHz, via an environment variable "cpuclk".
- Four compile-time constants are used:
- CONFIG_8xx_OSCLK - input quartz clock
- CFG_8xx_CPUCLK_MIN - minimum allowed CPU clock
- CFG_8xx_CPUCLK_MAX - maximum allowed CPU clock
- CONFIG_8xx_CPUCLK_DEFAULT - default CPU clock value
- If the "cpuclk" environment variable value is within the CPUCLK_MIN /
- CPUCLK_MAX limits, the specified value is used. Otherwise, the
- default CPU clock value is set.
- Please make sure you understand what you are doing, and understand
- the restrictions of your hardware (board, processor). For example,
- ethernet will stop working for CPU clock frequencies below 25 MHz.
- Please note that the new clock-handling code is enabled if
- CONFIG_8xx_CPUCLK_DEFAULT is defined. Since this mechanism supports
- only MPC866 and newer CPUs, this constant MUST NOT be defined for
- MPC823/850/860/862 series. The clock generation algorithm for older
- chips is different and has not been implemented yet. If you need it,
- your patch is welcome.
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