I'm having problems with the SDRAM of my custom board. I'm not yet running u-boot but testing the SDRAM setup with a debugger.
Basically it works. The problem also seems not to be a refresh problem:
1) If something is in the memory, the memory contents don't fade or change 2) Writing to memory seems to flip some bits, the faster the clock is, the more, it seems 3) Reading from memory also faciliates bit errors from time to time, but much less than writing to memory
I've tested this by writing a few KByte of text into the SDRAM and then reading it back, comparing the two files and counting the number of changed bytes with cmp -b -l <file1> <file2> | wc The result is that about 15% of the bytes are corrupted after writing the file two memory and reading it back.
If I read out the data from memory multiple times and compare the results of the reads, there is only a minor difference of about 1%. That's why I think the writing is the main problem.
I don't use burst reads/writes, only single reads/writes.
Any suggestions what is the probable reason for this behaviour?
I'm using an MPC875, programmed with microcode from a Micron SDRAM interfacing example + self-made SDRAM setup code.
Best regards,
Peter Asemann