AD9361 HDL - Inserting a FFT into the block design

On the current HDL release (2018_R1), data is passed as follows:

AD9361 Interface -> FIFO -> DMA Controller -> Interconnect

Technically you can put your IP anywhere, but the recommend place is here:

AD9361 Interface -> FIFO -> NEW IP -> DMA Controller -> Interconnect back to PS.

If you want to get both the pre and post FFT data just add another DMA+interconnect back to the PS for that additional datapath.

-Travis

Hi travisfcollins,

I'm doing a similar project using the hdl_2016_r2 release. There's no FIFO between AD9361 interface and dma controller. Can you help to clarify why the FIFO is added in 2018_r1 release?

Many thanks.

Hi, 

I am using hdl_206_r2 as well and it does indeed have a FIFO, I've attached an image of the branch from my console.

The FIFO can be seen in the block diagram as util_wfifo_v1.0 (please see attached image).

Cheers, 

Phil

Hi Phil, 

Sorry, I'm using 2015_r1 actually. After reading the release notes (https://github.com/analogdevicesinc/hdl/releases), I believe that FIFO can be removed without any impact if you don't need data loopback function.

Cheers.

I would highly recommend using the current release. It can be hard for us to answer questions about older releases, especially if the tools associated with those releases have limited support from their vendors.

In regards to the dataflow, you can put your DSP block before or after the pack blocks if you want, but know that there are 4 samples packed into the 64 bit output of the pack blocks, so your downstream processing must understand this interface. Data from the FIFO instead is clocked out at one sample at a time.

sqc_psg in regards to your IP, I would recommend reading the documentation on that core so you understand what those interfaces do. How you configure them is really up to you.

-Travis

Thanks travisfcollins. 

travisfcollins So your recommendation is to upgrade from hdl_2016_r2 to hdl_2018_R1? I will do that. Thanks for that advice.  

Regarding the implementation, I have read the documentation for the FFT(v9.0), util_cpack (AD core) and axi_ad9361(AD core) and from what I can tell, the FFT will assert waitstates on the S_TREADY line while processing data and requires the Master side (FIFO) to stop sending data at this time.  It doesn't look like util_cpack, util_wfifo or the axi_ad9361 have a signal which corresponds to processing that wait state.  

Do you have any examples at all of how you might connect the S_AXIS_TREADY signal in this chain so that the FFT buffers do not get flooded with samples and begin to drop them?

Also, the adc_sync signal on the FIFO side at the output of the packing function (util_cpack) indicates a sample of the first input channel, so this allows a downstream block (such as the FFT) to identify what are the correct I and Q samples.  the FFT does not appear to have a way of interpreting this either.

Any potential reference designs with a succesful implementation or advice would be very helpful.  dph , have you had any luck with implementing a FFT core into your block design?  If so, I'm very keen to hear how you achieved it. 

Best Regards, 

Phil

Hi Phil, 

It's still in progress. My FFT block only taps into the ADC data flow and write to a different DMA channel as I still need to keep the original captured data.

For your question above, I guess you can use a small FIFO before the FFT block just for flow control.

Cheers,

dph

Hi travisfcollins,

As you has been quite  prompt and helpful with the questions :) Can I ask a question which is not quite related to this thread?

In the release site, it says hdl_2018_r1 supports Vivado 2017.4. Is there any known issue with running hdl_2018_r1  with Vivado 2015.4? How about Vivado 2018.2? 

Many thanks,

dph

The transceiver must continuously transmit and receive data, unless in TDD mode, but I would not really recommend using this to control dataflow into your FFT block.  However, the FFT block should support a pipelined mode which will basically introduce a FIFO into the data stream and allow you to continuous process data, with a small latency hit though.

-Travis

Hi Travis, 

Thanks for your response and ongoing support.  After reviewing the block diagram and FFT pin options in detail, I was able to insert a FFT block in the design successfully.  

Thanks again. 

Phil

Hi Phil,

I know some years have passed by since you posted this question.

Just like you at the time, I also want to insert a FFT IP core to compute the spectrum of the received signal and currently I'm facing the exact same obstacles you had, so I'm very curious to know how you eventually solved it.

Like you once said, any potential reference designs with a succesful implementation or advice would be very helpful.

Kind regards,

Lars

Hi Phil,

I know some years have passed by since you posted this question.

Just like you at the time, I also want to insert a FFT IP core to compute the spectrum of the received signal and currently I'm facing the exact same obstacles you had, so I'm very curious to know how you eventually solved it.

Like you once said, any potential reference designs with a succesful implementation or advice would be very helpful.

Kind regards,

Lars