diff options
Diffstat (limited to 'u-boot/doc/README.MPC866')
| -rw-r--r-- | u-boot/doc/README.MPC866 | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/u-boot/doc/README.MPC866 b/u-boot/doc/README.MPC866 new file mode 100644 index 0000000..4707cb7 --- /dev/null +++ b/u-boot/doc/README.MPC866 @@ -0,0 +1,24 @@ +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 + CONFIG_SYS_8xx_CPUCLK_MIN - minimum allowed CPU clock + CONFIG_SYS_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. |