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>
Adam Graham