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SDRAM only work after refresh command


We are running NIOSII/F on a 10CL016YF484C8G from internal memory, but have issues with SDRAM(IS42S32200L). Without any delay after writing/reading the SDRAM data isn't always correct. About 10% correct. If we wait long enough(>15.625us) for the SDRAM refresh command to happen and then write or read will always works properly. 


We have the folowing settings

CAS latency: 3

Rerfresh command: 15.625ms

Delay after powerup: 100us

Duration of refresh command(t_rfc): 70ns

Duration of precharge command(t_rp): 20ns 

Active to Read or write delay(t_rcd): 20ns

Access time(t_ac): 5.4 ns

Write recovery time(t_wr): 26ns


We've tested with longer precharge time, access time, write recovery time, duration of refresh command. And used an PLL eventhough with worked also. None helped. We see a correlation with Refresh command, but can't explain why it's going wrong. Is it setting, HDL or board issue. Note it's a new board PCB. Any idea's. 


Best regards, 



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Hello, I believe you are asking about the SDRAM controller. Is the SDRAM controller that you mentioned here is Intel IP or your custom component? Is this happen on only one board or multiples board? This issue sound like is the SDRAM issue as its unable to retain the data without refresh even it still within the refresh period.

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