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sample value errors when using 4channel RX on FMCOMMS5

Question asked by mredfield on Feb 12, 2017
Latest reply on Feb 28, 2017 by CsomI

Hi everyone,


While testing my FMCOMMS5 4-channel receive code, I noticed that I sometimes get corrupted data on a channel. For example, if I am receiving on all four channels with the RF inputs left open, then I would expect to see low magnitude noise. Sometimes, I will instead see low magnitude noise with a lot of high magnitude spikes (1-sample wide). Here's an example of the behavior I'm seeing.

Those spikes in the data are all only a single sample wide. They all seem to be uncorrelated between I and Q.


When this happens, it almost always happens on channel 4 (though I think I've seen it on other channels). These corrupted samples sometimes go away if I reboot the system, but not always. Furthermore, if they are occurring then they may continue to occur even if I tweak radio settings such as center frequency, sample rate, RX gain and gain mode, etc.


The one thing that I've found that seems to make a difference is turning off in_voltage_bb_dc_offset_tracking_en for ad9361-phy-B. If I set that value to zero, the corrupted samples will sometimes disappear. If I set it to 1, then the corrupted samples will come back. It seems that this doesn't always work, though.


All of my tests have been performed with a stock FMCOMMS5/ZC702 setup (2016-r1, with ADI Update Tools and ADI Update Boot run immediately before the tests). The software I'm using is very similar to the iio-streaming C example, but adapted to use all 4 receive channels.


I haven't been able to figure out what exactly in_voltage_bb_dc_offset_tracking_en is doing. Is it possible there's an HDL error in the tracking module?