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how to calculate the time in table 44-8. MMDC Refresh Scheme

Question asked by Masatsugu Yamada on Apr 2, 2017
Latest reply on Apr 7, 2017 by Masatsugu Yamada

Hi,
I have a question about i.MX6 document,
http://www.nxp.com/assets/documents/data/en/reference-manuals/IMX6DQRM.pdf
p.3848, Table 44-8. MMDC Refresh Scheme.

 

The column "Description" of the table describes,

Option numberDescriptionREF_SEL
131,250 ns64 KHz
215,625 ns32 KHz

I understood the interval time in "Description" is related to REF_SEL, but I couldn't understand how to calculate.

 

My question is how to calculate the interval time described in "Description".
It seems the time is not inverse number of the frequency(REF_SEL).

 

However this interval time seems right from my experiment using DDR Stress Test.
I tried two test case (REFR is same value for purpose),
(1) REFR=0x3 REF_SEL=0 (64KHz)
(2) REFR=0x3 REF_SEL=1 (32KHz)
and (1) was failed within 400~500 loops, (2) was continued over 1000 loops.

 

Thanks in advance,
Yamada

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