Osmo-FL2K stops transmitting randomly

Sajjad Golchin poor sajjsamm at yahoo.com
Sat Jun 16 07:16:04 UTC 2018

Hi Marcus and thanks for your reply.

>Your video is about 13 minutes longer than I'd like – can you pinpoint
>at which time in that video your transmission stops?

You can watch this video between 7:00 & 8:00 to observe the breakdowns.

>As usual, debugging on the side of the observing party might very well
>be helpful here. Figure out whether the program halts (a software
>debugger, e.g. gdb, would be the appropriate tool), the USB transfers
>stop (wireshark might be helpful here), or whether just something
>happens inside the device while the computer and software happily
>continue to work. Observing the spectrum might help.

You just gave me a good point to start debugging this issue! Actually I don’t have a RTL-SDR or anything else in hand right now to observe the spectrum but I will do the tests soon.

Hi Steve, did a great job!

>This will happen if the host cannot supply enough data to the device,
>you need to use a lower sample rate in this case, or get rid of
>a hypervisor like VMware, as is the case in this video.

I tried fl2k_fm both in VMWare and in GNU radio live image booted from a flash drive and in both I had the problem. and why should I use a lower sample rate when my system can handle the samples well? (take a look at attachments)

I’m using VMWare Workstation Pro (Version: 14.1.2 build-8497320) on a brand new ACER laptop (Model: Aspire A715-71G-71Y3) running Windows 10 Pro 1803 (Build: 17134.112) with 16 gigabyte RAM and an Intel Core i7 7700HQ CPU. The USB host controller is Intel(R) USB 3.0 eXtensible Host Controller - 1.0 (Microsoft) witch I believe it can handle up to 157 MS/s. all drivers are updated. 
However, I didn’t see anything wrong with virtualization except that the maximum achievable sample rate was a little lower than the GNU radio live booted from flash drive. Except for this, I didn't encounter by anything.

>There seems to be a 'frame loss' mechanism to detect this in  through an
>interrupt transfer, but I haven't implemented this yet and have no idea
>if this works with disabled synchronization.

Looking forward to the results!
And don’t mind asking me for a helping hand. I’ll do my best to help this project.

I was reading the comments below this post in rtl-sdr.com blog and I saw a user who had the same issue mentioned something that might be useful:
Of futher note (hopefully someone from osmocom will see this) the bug where the broadcast intermittently ceases in fl2k_fm under both an ubuntu virtual machine and directly ran as a windows exe seems to have something to do with cpu affinity and / or process priority – generally it starts spitting out the underflow message on stdout then the signal drops out and the process requires a restart.
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