Sending single packets to a BladeRF

[Andreas Mueller]

Hi

I'm using GNU Radio in a test framework to test a physical Sub-GHz
transceiver. The setup is GNU Radio 3.8.2.0 with a flow graph in
Python that uses an osmosdr sink to push samples to a BladeRF in order
to simulate FSK packets. Once the flow graph is set up, I just call
self.start() and self.wait(). The goal is to send a single FSK packet
and then stop the processing. At a later point, I just add new data to
the message source and call start() and wait() again.

My problem is that GNU Radio never seems to push all samples to the
BladeRF. I think it is not an issue with the flow graph, because when
I replace the osmosdr sink with a file sink, the expected number of
samples is written to the file. When I use a file source directly
connected to an osmosdr sink however, not all samples from the file
are transmitted. I also believe its not an issue with the BladeRF,
because when I use bladeRF-cli to transmit samples from a file, things
are working as expected.

The following two workarounds help, but are not 100% reliable:

- adding lots of zeros after the actual samples
- adding a throttle block with the same sample rate right before the
  sink (from my understanding of GNU Radio, this makes no sense, but
  it does help)

Does anyone have any hints on how to solve this, or a better
workaround?

Thanks / best regards,
Andreas