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author | fishsoupisgood <github@madingley.org> | 2019-04-29 01:17:54 +0100 |
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committer | fishsoupisgood <github@madingley.org> | 2019-05-27 03:43:43 +0100 |
commit | 3f2546b2ef55b661fd8dd69682b38992225e86f6 (patch) | |
tree | 65ca85f13617aee1dce474596800950f266a456c /roms/u-boot/doc/README.MPC866 | |
download | qemu-master.tar.gz qemu-master.tar.bz2 qemu-master.zip |
Diffstat (limited to 'roms/u-boot/doc/README.MPC866')
-rw-r--r-- | roms/u-boot/doc/README.MPC866 | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/roms/u-boot/doc/README.MPC866 b/roms/u-boot/doc/README.MPC866 new file mode 100644 index 00000000..4707cb7d --- /dev/null +++ b/roms/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. |