AD9371 no-OS receive data using default DDS on TX


I was able to successfully build and run the example program for AD9371 no-OS for Intel/Altera Arria10 board using 2019_R1 branch. The DDS tone was selected to be 40Mhz, and we observe a 40MHz shift from the center frequency on the spectrum analyzer, as expected. The TX is looped back to RX. The example program runs a DMA operation and saves data in a buffer. If I extract that data and plot it, I don't see any meaningful information in the data. Both TX and RX LO frequency are set the same. I am wondering if I should expect the DDS frequency in the received data without any additional setting other than the defaults. Any details on the RX capture buffer would be helpful, ie.

1. Are the samples 32bit, with 16bit I (upper) + 16bit Q (lower)?

2. The ADCs are 12bit, are the receive values extended to 16bit?

3. Are the samples alternated between two channels? So if I am looping back just to RX1, should I get every even 32bit from the buffer

4. Does the receive values have a DC bias of 2^15 to get a full scale value 0-65535? or they are signed?


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