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authorAdam Graham <agraham@amcc.com>2009-02-09 13:18:12 -0800
committerStefan Roese <sr@denx.de>2009-02-12 06:08:07 +0100
commitc645012aefebb301e6907d148c6c8efacac049d4 (patch)
tree86c34e03b359c06f8e946dd2efcafdab9c739aee /board/amcc/taishan
parent2ede879fcb67470524847bb4fc8972651bb46184 (diff)
downloadblackbird-obmc-uboot-c645012aefebb301e6907d148c6c8efacac049d4.tar.gz
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ppc4xx: Autocalibration can set RDCC to over aggressive value.
The criteria of the AMCC SDRAM Controller DDR autocalibration U-Boot code is to pick the largest passing write/read/compare window that also has the smallest SDRAM_RDCC.[RDSS] Read Sample Cycle Select value. On some Kilauea boards the DDR autocalibration algorithm can find a large passing write/read/compare window with a small SDRAM_RDCC.[RDSS] aggressive value of Read Sample Cycle Select value "T1 Sample". This SDRAM_RDCC.[RDSS] Read Sample Cycle Select value of "T1 Sample" proves to be to aggressive when later on U-Boot relocates into DDR memory and executes. The memory traces on the Kilauea board are short so on some Kilauea boards the SDRAM_RDCC.[RDSS] Read Sample Cycle Select value of "T1 Sample" shows up as a potentially valid value for the DDR autocalibratiion algorithm. The fix is to define a weak default function which provides the minimum SDRAM_RDCC.[RDSS] Read Sample Cycle Select value to accept for DDR autocalibration. The default will be the "T2 Sample" value. A board developer who has a well defined board and chooses to be more aggressive can always provide their own board specific string function with the more aggressive "T1 Sample" value or stick with the default minimum SDRAM_RDCC.[RDSS] value of "T2". Also put in a autocalibration loop fix for case where current write/read/compare passing window size is the same as a prior window size, then in this case choose the write/read/compare result that has the associated smallest RDCC T-Sample value. Signed-off-by: Adam Graham <agraham@amcc.com> Signed-off-by: Stefan Roese <sr@denx.de>
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