Hi, I encountered this strange behavior when running fl2k_test on Windows 7: basically after a while the sample rate drifts and speeds up considerably. Sometimes it even starts up directly like that.
In the command prompt I get: C:\Users\Francesco Gugliuzza\Downloads\Sviluppo\FL2000fl2k_win_2018-08-09>fl2k_test.exe -s 138e6 Reporting PPM error measurement every 10 seconds... Press ^C after a few minutes. real sample rate: 146656386 current PPM: 62727 cumulative PPM: 62727 real sample rate: 150803676 current PPM: 92780 cumulative PPM: 77858 real sample rate: 149716182 current PPM: 84900 cumulative PPM: 80218 real sample rate: 150107883 current PPM: 87738 cumulative PPM: 82104 real sample rate: 150526750 current PPM: 90774 cumulative PPM: 83843
The same thing happens if I compile the latest osmo-fl2k myself using Cygwin. I'm running everything on a laptop with an i7 4710HQ CPU and 8 GB of ram, and I'm using a RayCue HDMI+VGA box.
Do you have an idea why the real sample rate drifts so much?
Thanks!
Hi,
On 20.10.2018 02:20, Francesco Gugliuzza wrote:
I encountered this strange behavior when running fl2k_test on Windows 7: basically after a while the sample rate drifts and speeds up considerably. Sometimes it even starts up directly like that.
Hm, I haven't seen this on Linux so far. Would be interesting to see if only the time measurement goes wrong (could be caused by CPU frequency scaling etc.), or if something is actually going wrong with the device or transfers.
fl2k_test outputs a rectangle signal, do you have an oscilloscope or an SDR you could use to check if the signal disappears when the measured sample rate starts to get strange?
Regards, Steve
Hi,
Il giorno mar 23 ott 2018 alle ore 19:00 Steve Markgraf steve@steve-m.de ha scritto:
Hi,
On 20.10.2018 02:20, Francesco Gugliuzza wrote:
I encountered this strange behavior when running fl2k_test on Windows 7: basically after a while the sample rate drifts and speeds up considerably. Sometimes it even starts up directly like that.
Hm, I haven't seen this on Linux so far. Would be interesting to see if only the time measurement goes wrong (could be caused by CPU frequency scaling etc.), or if something is actually going wrong with the device or transfers.
My two cents is that something is up with the actual data transmission, because I'm quite sure that the output signal gets corrupted or shifted out of frequency. The CPU is set to maximum performance, but turbo boost could effectively bring the frequency up by 200-300 MHz. I'm on a laptop with an i7 4710HQ.
fl2k_test outputs a rectangle signal, do you have an oscilloscope or an SDR you could use to check if the signal disappears when the measured sample rate starts to get strange?
Yes, I have a RTL-SDR, but I can't get my hands on it until next week. I will update you when I will manage to perform some tests. I can try on a live Linux distro if fl2k_test works correctly there, though.
Regards, Steve
Thank you!
Regards, Francesco
I have to start with an errata corrige: my laptop has Windows 8.1 and not 7, which is installed on another computer. Anyway, I've done some tests with a RTL-SDR, and I can definitely say that something goes wrong. When I start the rtl-test sometimes a peak appears at the correct frequency (e.g. if i set sampling at 100 MHz i find a peak at 3*100 - 50 = 250 MHz) and then disappears less than a second after; most times it doesn't even appear at all.
I've also tried running fl2k_test on Linux with a live DVD of Ubuntu 18.10 and everything seems to go well: it runs correctly even at high sample rates (150 MS/s), spewing out just an error on zero-copy buffers. Here is a log: ubuntu@ubuntu:~/osmo-fl2k$ fl2k_test -s 150e6 Allocating 6 zero-copy buffers libusb: error [op_dev_mem_alloc] alloc dev mem failed errno 12 Failed to allocate zero-copy buffer for transfer 4 Falling back to buffers in userspace Reporting PPM error measurement every 10 seconds... Press ^C after a few minutes. real sample rate: 149990146 current PPM: -66 cumulative PPM: -66 real sample rate: 150001491 current PPM: 10 cumulative PPM: -28 real sample rate: 150009752 current PPM: 65 cumulative PPM: 3 real sample rate: 149996142 current PPM: -26 cumulative PPM: -4 real sample rate: 150012666 current PPM: 84 cumulative PPM: 14 real sample rate: 150001814 current PPM: 12 cumulative PPM: 14 real sample rate: 150003433 current PPM: 23 cumulative PPM: 15 real sample rate: 149999114 current PPM: -6 cumulative PPM: 12 real sample rate: 149999349 current PPM: -4 cumulative PPM: 10 real sample rate: 150014477 current PPM: 97 cumulative PPM: 19 real sample rate: 149995547 current PPM: -30 cumulative PPM: 15 real sample rate: 150008611 current PPM: 57 cumulative PPM: 18 real sample rate: 149994234 current PPM: -38 cumulative PPM: 14 real sample rate: 150004040 current PPM: 27 cumulative PPM: 15 real sample rate: 150011047 current PPM: 74 cumulative PPM: 19 real sample rate: 149990169 current PPM: -66 cumulative PPM: 13 real sample rate: 150008286 current PPM: 55 cumulative PPM: 16 real sample rate: 149999384 current PPM: -4 cumulative PPM: 15
Using my RTL-SDR I find the peak at 3*150 - 75 = 375 MHz, as expected.
I will run some other tests on my other computer, the one with Windows 7.
Have a nice evening, Francesco
-
Francesco Gugliuzza -
Steve Markgraf