ls1046 ddr4 frequency at calibration process

[altu]

Good day!

I'm calibrating DDR4 memory on my custom ls1046-based board.

My RCW settings:

SYS_PLL_RAT=6
MEM_PLL_RAT=12
CGA_PLL1_RAT=12
CGA_PLL2_RAT=10

SYSCLK_FREQ=600

DDR_REFCLK_SEL=1
DDR_FDBK_MULT=2

My SYSCLK = 100 Mhz

ddr1.png

I expect to have:

DDR bus clock = 600 Mhz and DDR rate = 1200 MT/s , but I have DDR bus clock = 625 Mhz and DDR rate = 1250 MT/s.

ddr2.png 

So the question is - why do we have addtional 25 Mhz / 50 MT/s ?

[altu]

I understand,thank you very much!

[June_Lu · Accepted solution]

LS1046A DDR4 Min Freq.(MHz) is 650MHz, as specified in the LS1046A, LS1026A Data Sheet, Table 141. Memory bus clocking specifications

Kindly refer to this requirement in your design.

Thanks