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>
After changing SDRAM_CLKTR phase value rerun the memory preload
initialization sequence (INITPLR) to reset and relock the memory
DLL. Changing the SDRAM_CLKTR memory clock phase coarse timing
adjustment effects the phase relationship of the internal, to the
PPC chip, and external, to the PPC chip, versions of MEMCLK_OUT.
Signed-off-by: Adam Graham <agraham@amcc.com>
Signed-off-by: Victor Gallardo <vgallardo@amcc.com>
Signed-off-by: Stefan Roese <sr@denx.de>
Alternate SDRAM DDR autocalibration routine that can be generically used
for any PPC4xx chips that have the IBM SDRAM Controller core allowing for
support of more DIMM/memory chip vendors and gets the DDR autocalibration
values which give the best read latency performance (SDRAM0_RDCC.[RDSS]).
Two alternate SDRAM DDR autocalibration algoritm are provided in this patch,
"Method_A" and "Method_B". DDR autocalibration Method_A scans the full range
of possible PPC4xx SDRAM Controller DDR autocalibration values and takes a
lot longer to run than Method_B. Method_B executes in the same amount of time
as the currently existing DDR autocalibration routine, i.e. 1 second or so.
Normally Method_B is used and it is set as the default method.
The current U-Boot PPC4xx DDR autocalibration code calibrates the IBM SDRAM
Controller registers.[bit-field]:
1) SDRAM0_RQDC.[RQFD]
2) SDRAM0_RFDC.[RFFD]
This alternate PPC4xx DDR autocalibration code calibrates the following
IBM SDRAM Controller registers.[bit-field]:
1) SDRAM0_WRDTR.[WDTR]
2) SDRAM0_CLKTR.[CKTR]
3) SDRAM0_RQDC.[RQFD]
4) SDRAM0_RFDC.[RFFD]
and will also use the calibrated settings of the above four registers that
produce the best "Read Sample Cycle Select" value in the SDRAM0_RDCC.[RDSS]
register.[bit-field].
Signed-off-by: Adam Graham <agraham@amcc.com>
Signed-off-by: Stefan Roese <sr@denx.de>
