# Re: U's and L's when running GNU Radio **URL:** \ **Category:** GNU Radio\ **Created:** [January 12, 2015, 3:19pm UTC](https://www.ruby-forum.com/t/re-us-and-ls-when-running-gnu-radio/233790 "2015-01-12T15:19:29Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\ **Post date:** [January 12, 2015, 3:19pm UTC](https://www.ruby-forum.com/t/re-us-and-ls-when-running-gnu-radio/233790/1 "2015-01-12T15:19:29Z")
Hi Marcus, Hi Sylvain, Thank you for your response. I continue to get these ULLLLLLLLLLLLLLLL even on a PC with really high specs. Please find below my answers to your questions. > > Do you use timed\_commands? Yes, I do. In the python script, I simply use get\_time\_now() to query the times of both the Sink and the Source. Then, I convert this to a format understandable to python and I keep hold of the greater time of the two, I call it start\_delay. Then, using set\_start\_time(), I make sure that both the Sink and the Source start at time start\_delay. Is there any problem with my timed\_commands? > > What are your RX and TX sampling rates? It’s 100e06/256 = 390,625 Hz for both Tx and Rx. > > From your network throughput, I’d assume your using 4x 3.3MS/s, is that > > correct? I am using four Rx channels, and just one Tx channel. Based on the NW history in the link below, [![](https://lists.gnu.org/archive/html/discuss-gnuradio/2015-01/png5hOoJln6ra.png) ](https://lists.gnu.org/archive/html/discuss-gnuradio/2015-01/png5hOoJln6ra.png) My throughput is around 1.6 MB/s for each channel. This is set automatically by GNU Radio. Do I need to adjust it? Thank you. Best regards, Khalid _Re: U’s and L’s when running GNU Radio [https://www.ruby-forum.com/topic/6812736#1166236](https://www.ruby-forum.com/topic/6812736#1166236)_ [image: D17685d174fee4ca258c75cce7bc2202?d=identicon&s=25] Marcus Müller (Guest) on 2015-01-07 15:24 [image: (Received via mailing list)] Hello Sylvain, hello Khalid, these could be underruns (U) and late (L) packets, as reported by UHD, used via gr-uhd; however, seeing so many L’s is a very uncommon pattern; Do you use timed\_commands? What are your RX and TX sampling rates? From your network throughput, I’d assume your using 4x 3.3MS/s, is that correct? Could you share the whole output of your program’s run, not only the ULLLL… ? Best regards, Marcus _Re: U’s and L’s when running GNU Radio [https://www.ruby-forum.com/topic/6812736#1166229](https://www.ruby-forum.com/topic/6812736#1166229)_ [image: 0817fa933c74eec9b3fcf3a04e16f418?d=identicon&s=25] Sylvain Munaut (Guest) on 2015-01-07 14:48 [image: (Received via mailing list)] Hi, > In the terminal and while using a powerful PC (please see the attachment), I\> am > occasionally getting capital U’s and L’s when running GNU Radio with one\> Tx and 4 > Rx channels (Here is a sample of what I am getting:\> > ULLLLLLLLLLLLLLLULLLLULLLLLLLLLLLLLLLULLLULLLLLLLLLLLLLLLLLLLLLLLLLLLL). I can’t find anything in GNURadio itself that would print that. The only thing it can print AFAICT is aU aO jU So it must be an OOT block that display those … Cheers, Sylvain _U’s and L’s when running GNU Radio [https://www.ruby-forum.com/topic/6812736#1166051](https://www.ruby-forum.com/topic/6812736#1166051)_ [image: 03a87ab164b2170c1bb9750462ca0053?d=identicon&s=25] Khalid Eldarymli (khalide [https://www.ruby-forum.com/user/show/khalide](https://www.ruby-forum.com/user/show/khalide)) on 2015-01-05 17:50 [image: (Received via mailing list)] Attachment: SystemMonitor.png [https://www.ruby-forum.com/attachment/10372/SystemMonitor.png](https://www.ruby-forum.com/attachment/10372/SystemMonitor.png) (100 KB) [https://www.ruby-forum.com/attachment/10372/SystemMonitor.png](https://www.ruby-forum.com/attachment/10372/SystemMonitor.png) Hi, In the terminal and while using a powerful PC (please see the attachment), I am occasionally getting capital U’s and L’s when running GNU Radio with one Tx and 4 Rx channels (Here is a sample of what I am getting: ULLLLLLLLLLLLLLLULLLLULLLLLLLLLLLLLLLULLLULLLLLLLLLLLLLLLLLLLLLLLLLLLL). Please note that I am using timed-commands to start both the Tx and Rx’s at the same time. When I check the System Monitor while GNU Radio is running (please see the attachment), the CPU history and RAM usage seem to be fine. Also, swap memory is disabled as shown in the attachment. What causes this issue and how to handle it? Could it be due to some instability in the writing speed to the hard drive? BTW, I am having the same issue for my older PC (a PC with less specs). The System Monitor tells me that my CPU usage is around 60% and my RAM usage is around 45%, however, I am getting U’s and L’s when I try to use four Rx channels. Please note that the system doesn’t throw lots of U’s and L’s at once, it is a kind of frequent where a bunch of them are thrown out every many seconds or so. Thanks in advance for your help. Best regards, Khalid ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 12, 2015, 7:09pm UTC](https://www.ruby-forum.com/t/re-us-and-ls-when-running-gnu-radio/233790/2 "2015-01-12T19:09:14Z")
Hello Khalid, On 01/12/2015 03:18 PM, khalid.el-darymli wrote: > Hi Marcus, Hi Sylvain, > > Thank you for your response. I continue to get these ULLLLLLLLLLLLLLLL > even on a PC with really high specs. > My suspicion is that the ULLL… don’t stem from your PC being too slow, > but from the fact that you try to transmit packages in the past. > Is there any problem with my timed\_commands? > That’s hard to tell without having a look at your code; would you mind > posting the part where you calculate your command times? > > > > What are your RX and TX sampling rates? > > > It’s 100e06/256 = 390,625 Hz for both Tx and Rx. > > > > From your network throughput, I’d assume your using 4x 3.3MS/s, is that > > > correct? > > > I am using four Rx channels, and just one Tx channel. Based on the NW > > > history in the link below, > > > My brain had a glitch, and I was of by a factor of 10… ah well. > > [https://lists.gnu.org/archive/html/discuss-gnuradio/2015-01/png5hOoJln6ra.png](https://lists.gnu.org/archive/html/discuss-gnuradio/2015-01/png5hOoJln6ra.png) > > My throughput is around 1.6 MB/s for each channel. This is set > automatically by GNU Radio. Do I need to adjust it? > You can’t adjust that 🙂 it’s just the data rate induced by the sampling > rate, from which I tried (and failed) to estimate your sampling rate. Greetings, Marcus