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Dependency of tCL and tCWL values on custom hardware performance ?

Question asked by Peter Amond on Sep 3, 2018
Latest reply on Sep 3, 2018 by Yuri Muhin

Hi All,

Yuri Muhin



My custom hardware is based on i.MX6Q processor and 800MHz Alliance DDR3 memory AS4C256M16D3A-12BCN.Design is most related to Nitrogen6_max design.


I set tCL = 6 and tCWL = 8 for the calibration and ddr init script. Some boards are working for this values and for some boards I had to change tCWL = 7 for better performance. Otherwise getting segmentation faults.


1) How this could happen with the same ddr layout and same production line boards ?  What can we figure with this fine tuning of tCL and tCWL value of board to board ?



A well as I could see following write DQS delays for my boards. You can see DQS 3 and DQS 4 are way off. It should be lover than 1/8 according to NXP user manual. 


2) What can we say from following DQS results ? Is it a impedance problem of those byte lanes ? 



3) To optimize above values I used following method. But I couldn't see any impact for DQS 3 and DQS 4 with WALAT changes. Why is that ?




4) What are the other dependency which we can tolerate like tCWL and tCL for the memory performance ? 



Here I have attached DDR3 memory data sheet and NXP calibration tool results. 


I must be thankful to you if you will kindly reply me soon.