Possible buffering issue in Modem-Example0

[Marissa-vW]

EDIT: Looking through the other SoapySDR device repos, it seems as though getHardwareTime( ) is a common function they have, but we can't seem to find it in the SoapyRedPitaya source code, even though the modem example requires this. Is there a workaround?

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Making use of the Pothos Flow modem demo (found here: https://github.com/pothosware/PothosDemos/wiki/Modem-Example0), I was able to transmit messages from the OUT1 channel to IN1 channel of a Red Pitaya STEM 125-14 board. Some chatbox messages weren't received at all, while others would have an incorrect letter, or be a duplicate of a previous message. I don't believe that these issues are due to channel loss, as the input and output ports are connected directly.

When replacing the transmission side's chat box with a message generator, and using text file sinks at the output of this block, and the end of the receiving diagram, I get the below output. Some bytes are received (green), repeated from previous messages (blue), or missing completely (red). Is this a buffer issue of some sort, or is this related to block settings?

Any guidance would be a huge help, as I'm trying to develop a system using 2 of these boards, and would like to make sure everything functions correctly before moving on.

[pavel-demin]

I'd suggest to check the CPU load and the network bandwidth usage on the PC running Pothos.

Maybe the 1.25 MSPS sample rate is too high.

[Marissa-vW]

I'd suggest to check the CPU load and the network bandwidth usage on the PC running Pothos.

Maybe the 1.25 MSPS sample rate is too high.

We've tried numerous combinations of sink/source centre frequency and sampling rates (including a 5e5 sample rate with an SDR sink/source centre frequency of 1e5, obeying Nyquist's theorem) but to no avail.

[pavel-demin]

When I tested Red Pitaya with Pothos, it worked for me without any problem.

Here is a screenshot showing my test configuration:

If there are buffering problems, then it should be seen on the spectrum. However, the spectrum is clean. So, I believe that the problem is somewhere else.

[pavel-demin]

I've just noticed your update about getHardwareTime().

I don't have any idea how to implement it in SoapyRedPitaya.

[Marissa-vW]

When I tested Red Pitaya with Pothos, it worked for me without any problem.

Here is a screenshot showing my test configuration:

If there are buffering problems, then it should be seen on the spectrum. However, the spectrum is clean. So, I believe that the problem is somewhere else.

I've built your configuration and it appears to be fine, so the problem is most likely related to the timing trigger.

On a side note, is there any way to set the carrier amplitude of the Red Pitayas? (We're currently using 2 boards loaded with the SD card image from your Red Pitaya notes site.)