1The current implementation allows the user to specify the desired CPU 2clock value, in MHz, via an environment variable "cpuclk". 3 4Four compile-time constants are used: 5 6 CONFIG_8xx_OSCLK - input quartz clock 7 CONFIG_SYS_8xx_CPUCLK_MIN - minimum allowed CPU clock 8 CONFIG_SYS_8xx_CPUCLK_MAX - maximum allowed CPU clock 9 CONFIG_8xx_CPUCLK_DEFAULT - default CPU clock value 10 11If the "cpuclk" environment variable value is within the CPUCLK_MIN / 12CPUCLK_MAX limits, the specified value is used. Otherwise, the 13default CPU clock value is set. 14 15Please make sure you understand what you are doing, and understand 16the restrictions of your hardware (board, processor). For example, 17ethernet will stop working for CPU clock frequencies below 25 MHz. 18 19Please note that the new clock-handling code is enabled if 20CONFIG_8xx_CPUCLK_DEFAULT is defined. Since this mechanism supports 21only MPC866 and newer CPUs, this constant MUST NOT be defined for 22MPC823/850/860/862 series. The clock generation algorithm for older 23chips is different and has not been implemented yet. If you need it, 24your patch is welcome. 25