[U-Boot-Users] Why the contents in SDRAM stay?
Hi all,
I am playing with the u-boot that is just installed on my customed board with PPC405GP (based on walnut). The SDRAM I am using is SAMSUNG K4S561632D-TC75000.
One interesting thing I found is, I used mm to change the first 4 bytes at address 0, which is suppose to belong to SDRAM, to 0xdeaddead. Then I turned off the power. After I turned on the power, I used md to check the memory. The content at address 0 was still 0xdeaddead. I changed the value several times and found once I modified the SDRAM, the content stays regardless the power is off. This is very weird. Should the content be lost once the power is off? Can anybody explain how it happened?
BTW, after I turn off the board I waited for long enough (1-2 minutes) to turn it on.
Thanks,
Frank
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In message BAY2-F33TWyebkWdh8B000e6fc2@hotmail.com you wrote:
One interesting thing I found is, I used mm to change the first 4 bytes at address 0, which is suppose to belong to SDRAM, to 0xdeaddead. Then I turned off the power. After I turned on the power, I used md to check the memory. The content at address 0 was still 0xdeaddead. I changed the value several
That's not interesting, it's normal with good RAM chips.
BTW, after I turn off the board I waited for long enough (1-2 minutes) to turn it on.
That's not long enough. Wait a day :-)
Or check memory by running a checksum (crc32 command) over a largaer area - say 1 MB, and then try again. You will see that while most cells keept their content, some don't.
Best regards,
Wolfgang Denk
participants (2)
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Frank Young -
Wolfgang Denk