TMS320C6678: DDR3 leveling: Can't read/write DDR3 at 666.7MHz

Hello Champs,

Customer used Micron MT41K256M16HA-125IT 1600M.

When configuring 666.7Mhz in <DDR3 Register Calc v4.xlsx> and <DDR3 PHY Calc v11.xlsx>, the MT41K256M16HA runs at 666.7Mhz, too, but the DDR3 can't read/write correctly. 

But when configuring 800MHz in <DDR3 Register Calc v4.xlsx> and <DDR3 PHY Calc v11.xlsx>, the MT41K256M16HA runs at 666.7Mhz, the DDR3 can read/write correctly. 

Below is the parameters configured in DDR3 Register Calc v4.xlsx at 800MHz.



It is very curious. He also changed the parameters in DDR3 PHY Calc v11 according to his own pcb layout. He used fly by topology, DQS and CLK are differential signal.

Microstrip length (inches) Stripline length (inches) Delay (ps)
DQS0 0.000 1.336 223
CK_0 0.000 2.608 436
DQS1 0.000 1.205 201
CK_1 0.000 2.608 436
DQS2 0.000 1.171 196
CK_2 0.000 3.090 516
DQS3 0.000 1.094 183
CK_3 0.000 3.090 516
DQS4 (C665x DQS0) 0.000 1.252 209
CK_4 (C665x CK_0) 0.000 4.066 679
DQS5 (C665x DQS1) 0.000 1.159 194
CK_5 (C665x CK_1) 0.000 4.066 679
DQS6 (C665x DQS2) 0.000 1.391 232
CK_6 (C665x CK_2) 0.000 4.543 759
DQS7 (C665x DQS3) 0.000 1.385 231
CK_7 (C665x CK_3) 0.000 4.543 759
DQS_ECC 0.000 0.997 166
CK_ECC 0.000 3.574 597

Thanks.
Rgds
Shine