B200 overrun causes flowgraph to freeze

[radio-dan]

Issue Description

When running a GRC flowgraph using a UHD: USRP Source with a B200, if the flowgraph is slow enough that an overrun results from USRP, the entire flowgraph freezes permanently.

Setup Details

Linux Mint 20 running in VirtualBox hosted on Windows 10
USRP B200 connected via USB 3
UHD_4.0.0.0-0-g90ce6062
Gnuradio maint-3.8 branch, b0619899

Expected Behavior

Continuous overruns reported and flowgraph tries to keep up.

Actual Behaviour

A single overrun is reported and the flowgraph freezes.

Steps to reproduce the problem

A GRC flowgraph consisting of just a USRP Source -> QT GUI Frequency Sink, attempting to run at 40Msps sample rate.

Additional Information

This problem does not occur when building from UHD-3.15.LTS (UHD_3.15.0.0-54-gbc585b43

[radio-dan]

Example GRC
b200 test.grc.zip

[mbr0wn]

Confirmed with uhd_fft.

[michael-west]

The root cause has been found and fixed on the master branch (commit 70e1f0f). Thanks for reporting!