File Meta Source causes huge lag at end of file when used with repeat = True

[Adrian Winter]

Hey,

 

I’m pretty sure that I discovered another bug in File Meta Source, but maybe this is known behavior or user error.

 

Short Summary:

 

When using File Meta Source with Repeat = True, there is a very noticeable lag (ca 500 ms) when the file “rewinds” to the beginning, at least when reading at high sample rates.

 

Setup:

    *   GNURadio 3.10.9.2

    *   Python 3.11.8

    *   Installed through radioconda

    *   X86-64 running Ubuntu 20.04 LTS

    *   Ettus Research USRP B200

    *   UHD 4.6.0.0

 

Steps to Reproduce:

 

1. Create a IQ file using File Meta Sink with enough samples for approx. 1s at the chosen sample rate (40-56 MS/s, see note below)
2. Replay the file using  a File Meta Source into a UHD USRP Sink.
3. Observe the TX light on the USRP.

 

Observed Behavior:

The TX light blinks. Underflow messages on the console are created

 

Expected behavior:

The TX light stays on without interruption. No underflow messages created.

 

 

Workaround:

Introduce a block in-between the File Meta Source and the USRP sink and set the minoutbuf value in the advanced settings to a large value, e.g. enough samples for 1 s. Tested with Throttle block (and maximum rate set to something higher than the sample rate), as well as a IShortToComplex block, but presumably any block works. Essentially, this block then becomes a buffer for whenever the File Meta Source is too slow. Setting minoutbuf on the File Meta Source does NOT work.

 

 

The attached video in the zip file clearly demonstrates this. The upper USRP is running the version without the workaround, the lower USRP the one with the workaround.

 

Notes:

• Due to issue #7191, this must be done with a file with inline headers, otherwise the repetition will not work
• This problem may not occur or may be less obvious when using lower sample rates, I didn’t check.
• This does not occur when using the File Source
• Using a ramdisk does not fix the issue

 

 

Please let me know if you have any other ideas, else I’ll create another issue on Github!

 

Thank you!

Adrian Winter

file_meta_source_lag.zip
Description: file_meta_source_lag.zip