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FMCOMMS1/KC705 with no OS - DMA

Question asked by Chris449 on Jul 1, 2016
Latest reply on Jul 11, 2016 by Chris449

Hi all,

I am using the FMCOMMS/KC705 reference design with no OS.

DAC AD9122 samples at 983.04MHz with interpolation = 8, DCI signal  = 122.88MHz and DAC_clk from FMCOMMS1 = 122.88MHz.

 

When I am using the DDS to generate the signal, no problem, the tones are well positioned.

 

When I am using the DMA, the distance between the tones is twice smaller of what it should be and I can see the images on each side of the spectrum.

 

In the SDK, to test the problem, I modified your DMA test example:

 

uint16_t sine_lut_i[32] = {

0,65535,0,65535,0,65535,0,65535,

0,65535,0,65535,0,65535,0,65535,

0,65535,0,65535,0,65535,0,65535,

0,65535,0,65535,0,65535,0,65535,

 

}

and

data_I = data_q = sine_lut_i[index]

 

When I check the DCI line with the scope, signal frequency = 122.88MHz.

However, the data DAC line frequency is 30.72MHz, I expected 61.44MHz due to the DDR for I and Q (I=Q in word mode).

It seems that the data are played twice which will explain my tone spacing/image problem.

Is it the frequency of the memory that is not what it is supposed to be so the samples are read twice?

Thanks for your help.

 

Best,

Chris

 

 

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