[U-Boot-Users] Query regarding PSDMR register values.

Jerry Van Baren gerald.vanbaren at smiths-aerospace.com
Thu Jan 20 14:20:49 CET 2005

Apoorv_Sangal wrote:
> Hello All,
> I am customizing Uboot for PowerQuiccII 8266 based PMC card.
> Can anyone please let me know how the value of the PSDMR register is
> obtained / calculated?
> We are using MT48LC16M16A2 SDRAM (SODIMM). Specifically, we are looking or
> the values of RFRC, PRETOACT, ACTTORW, LDOTOPRE and WRC fields in PSDMR. The
> datasheet of SDRAM gives those values in nanoseconds.
> But the PSDMR register in Uboot needs values in clock cycles.
> Can anyone please tell me how to calculate the values for the required
> fields (in clock cycles) from the values in the datasheet (in nanosecs)?
> Thanks & Regards,
> Apoorv Sangal.

freq = 1/time
time = 1/freq
clock cycles = time * freq

Pick the one that matches the problem and use consistent units.

Read the 8266 User's Manual and your board documentation/schematic to 
determine the frequency that your CPU is clocked at.  Use the "ceiling" 
function on your clock cycles calculation (i.e. "round up").


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