Frank,

I think you power off and then immediately (in a few seconds) power on the board. If you stay a while after you power off the board, the content of SDRAM should be lost.

The reason is that sdram keeps the contents for a while without refresh.

Hope this helps.

Jihua

From: "Frank Young" young726@hotmail.com To: u-boot-users@lists.sourceforge.net Date: Tue, 13 Jul 2004 17:54:11 -0700 Subject: [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