[U-Boot-Users] Dynamic SDRAM Config on MPC8245

Chris Hallinan clh at net1plus.com
Thu Feb 6 16:21:43 CET 2003

Hi all,

We have a request to support dynamic SDRAM detection and
configuration on an MPC8245-based custom board.  We are currently
running PPCBoot-1.2.0 on the board (haven't had time to upgrade)
though we have a reasonably recent U-Boot source tree for reference.
Basically, we want to be able to drop in different SDRAM SODIMM
modules and have the integrated SDRAM controller set up correctly on
boot, much like a PC does.

We have I2C enabled, and we can read the Serial Presence Detect
EEPROM on the SODIMM, but this code in U-Boot requires SDRAM already
running.  The difficulty on 8245 is the MEMGO bit, which the way I
read it, you risk losing SDRAM data when you change SDRAM
configuration on the fly.

There are 2 options which come to mind:
1) Write a simple I2C read routine in assembler capable of running
without DRAM to read Presence Detect EEPROM, decode and apply
settings (moderate effort) or

2) Change the settings on the fly after booting and setting SDRAM
for 'worst case' timings and bank settings.  (much easier effort, as
much of the code exists in U-Boot to do this.

Not sure if 2 will corrupt SDRAM or not.

Has anyone looked at this on 8245 or like processors/SDRAM
controllers?  We'd like to hear comments/opinions.


Chris Hallinan
DS4.COM, Inc

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