osmocom-sdr November 2013

osmocom-sdr@lists.osmocom.org

15 participants
16 discussions

RTL-SDR source in GNU-Radio 3.7.1 weird behaivour at 900 ksps
by Miguel A. Vallejo 13 Nov '13

13 Nov '13

Hi again. I noticed a strange behaivour from RTL-SDR source in GNU-Radio 3.7.1 When sample rate is set to 900ksps, actual output sample rate is only 300 ksps. You can check this easily connecting a RTL_SDR Source to a WX Gui FFT Sink and a RF signal generator. For example, on RTL-SDR Source set sample rate to 900000 and frequency to 144000000 Hz. On the WX GUI FFT Sink, set sample rate to 900000 and base frequency to 144000000 Hz. Now apply a signal on 144.1 MHz. The FFT Display will show it at 144.3 MHz. Apply a signal on 144.05 MHz. The FFT Display will show it at 144.15 MHz. Now on the WX GUI FFT Sink, set sample rate to 300000 and repeat the above steps. The signal will be displayed at its right places. Interestingly, setting sample rate to 1Msps works fine. Tested with both E4000 and R820T dongles. Any advice? Thank you!

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rtl_fm and r820t tuner
by Miguel A. Vallejo 13 Nov '13

13 Nov '13

Hello! I noticed a problem with rtl_fm and r820t tuners. In few words, it doesn't matter what value of gain you set with the -g parameter. The r820t tuner will be always at its lower gain, this is deaf as a doorknob. Otherwise, the same dongles works fine with GNU Radio or GQRX for example, and gain can be set without problems. rtl_fm gain works nicely on e4k tuners. Someone else have noticed this?

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Latest commit of gr-osmocom (v0.1.0-44-g0d10f5e9 / 0.1.1git) fails to build
by Joel 13 Nov '13

13 Nov '13

Hello, Make ouputs the following error messages when building the latest commit of gr-osmocomsdr [rev:0d10f5e9bc950d6d2b3c39ae574e2d325a0fbeb6] $ make Scanning dependencies of target gnuradio-osmosdr [ 2%] Building CXX object lib/CMakeFiles/gnuradio-osmosdr.dir/source_impl.cc.o [ 5%] Building CXX object lib/CMakeFiles/gnuradio-osmosdr.dir/sink_impl.cc.o [ 8%] Building CXX object lib/CMakeFiles/gnuradio-osmosdr.dir/ranges.cc.o [ 11%] Building CXX object lib/CMakeFiles/gnuradio-osmosdr.dir/device.cc.o [ 13%] Building CXX object lib/CMakeFiles/gnuradio-osmosdr.dir/fcd/fcd_source_c.cc.o [ 16%] Building CXX object lib/CMakeFiles/gnuradio-osmosdr.dir/file/file_source_c.cc.o [ 19%] Building CXX object lib/CMakeFiles/gnuradio-osmosdr.dir/rtl/rtl_source_c.cc.o /home/joel/src/gr-osmosdr/lib/rtl/rtl_source_c.cc: In member function ‘virtual osmosdr::freq_range_t rtl_source_c::get_freq_range(size_t)’: /home/joel/src/gr-osmosdr/lib/rtl/rtl_source_c.cc:467:26: error: ‘RTLSDR_TUNER_R828D’ was not declared in this scope } else if ( tuner == RTLSDR_TUNER_R828D ) { ^ make[2]: *** [lib/CMakeFiles/gnuradio-osmosdr.dir/rtl/rtl_source_c.cc.o] Error 1 make[1]: *** [lib/CMakeFiles/gnuradio-osmosdr.dir/all] Error 2 make: *** [all] Error 2 OS: Fedora 19 x64 I am currently using the previous commit: b8441496288aa319f4aeaabd9df63c58be53e916 which builds fine on my workstation. I haven't tested the commits made between this and the latest revisions. Regards, Joel

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FW: multiple devices in one process?
by Jay Salsburg 13 Nov '13

13 Nov '13

Woops, the mistake I am making is that the dongles are independent USB devices, there is no way to synchronize each Dongle's Acquisition. This is another reason to interface these Dongles with a BusPirate and 24bit Audio Board. From: osmocom-sdr-bounces(a)lists.osmocom.org [mailto:osmocom-sdr-bounces@lists.osmocom.org] On Behalf Of Jay Salsburg Sent: Tuesday, November 12, 2013 3:58 PM To: osmocom-sdr(a)lists.osmocom.org Subject: RE: multiple devices in one process? USB 2.0 has a built-in hardware latency. If you are unwilling to go through the trouble of special coding, be sure to use the USB Dongles alone on their own PCI USB Card, this will minimize latency. Hardware may be forced to respond at will if Assembly Code is used to exercise the interfaces, utilizing acquisition calls controlled by processor interrupts. A Real Time Clock (RTC) in internal Hardware or an external RTC can be used to trigger Processor Interrupts initiating any function in the (Assembly) code and attached hardware. Using a patch will not work with any reasonable accuracy, depending on the Hardware, (an educated guess) of a many microseconds. Patching indicates high level control (high level language like C++, Python, etc), only low level control will call the hardware anywhere near the timing desired. If you are to access two different devices, their data should be both buffered together in parallel through a first-in-first-out buffer, perhaps even with the RTC time stamp to quantize the packets therefore allowing subsequent coherence in post processing. In high speed audio and video interfaces, very high speed is used, like Firewire and Thunderbolt to stream the data into memory, eliminating most of the hardware latency you are experiencing. The maximum acquisition rate for USB 2.0 is about 48,000 samples per second, times 24 bit depth, times 8, and that is for a fast computer doing nothing else but recording the data stream. From: osmocom-sdr-bounces(a)lists.osmocom.org [mailto:osmocom-sdr-bounces@lists.osmocom.org] On Behalf Of Michel Pelletier Sent: Sunday, November 10, 2013 11:14 PM To: osmocom-sdr(a)lists.osmocom.org Subject: multiple devices in one process? I've been thought-experimenting with capturing data from two devices and measuring their correlation. For example, if two rtl-sdr processes are launched to read one sample block from two devices, how closely do the two devices' samples line up with each other in time? I'm expecting that there will be no reliable correlation. My working theory is that each process calls into libusb_handle_events_timeout according to its own process schedule and that there is no way to coordinate these two calls to happen closely enough in time for the transfers to happen in a more synchronized fashion. Threads do not appear to be any better solution to the problem. I'm not an expert in usb transfers, or libusb, or rtlsdr for that matter, so I'm going only on what I can glean from reading the source code of librtlsdr.c and libusb documentation. libusb does say however that it can specifically handle multiple devices in one async loop. Multiple bulk transfers can be set up to multiple devices in one process, and one call to libusb_handle_events_* can be used to handle those transfers. My thinking is that because the triggering event for both samples is now the same function call in the same process, the samples will be more synchronized, ideally down to some reliably offset of say a few microseconds. Juha Vierinen's hard-hack to make two devices use a coherent sample clock makes this idea even more interesting to me. But, it doesn't look like librtlsdr can handle multiple devices. I'm game to take a stab at a patch that can extend its functionality. But I wanted to run this idea by the community first before spending code time on figuring this out. Do the experts here think that there is any potential benefit to be gained by taking this approach? -Michel _____ No virus found in this message. Checked by AVG - www.avg.com Version: 2013.0.3426 / Virus Database: 3222/6830 - Release Date: 11/12/13 _____ No virus found in this message. Checked by AVG - www.avg.com Version: 2013.0.3426 / Virus Database: 3222/6830 - Release Date: 11/12/13

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Re: multiple devices in one process?
by Peter Stuge 12 Nov '13

12 Nov '13

David Jacobowitz wrote: > So, is there any way to line up samples post-hoc? Of course you can develop an elaborate hardware+software system to inject, recover, and sync onto an in-band clock. Or you could just buy hardware which already does what you need. //Peter

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Fwd: rtl_test patch
by Nuno Gonçalves 02 Nov '13

02 Nov '13

I'm not sure it this was overlooked or if I should format it any other way... Regards, Nuno ---------- Forwarded message ---------- From: Nuno Gonçalves <nunojpg(a)gmail.com> Date: Sun, Apr 21, 2013 at 6:59 PM Subject: rtl_test patch To: osmocom-sdr(a)lists.osmocom.org Corrects bugs where: Cumulative PPM error is always "342" if execution stopped before first PPM_DURATION. PPM error alias to wrong values if over +-1045 (this happens quite a lot actually due to bug reported at [1]). Behavior changes: Cumulative PPM error value is now printed every PPM_DURATION so the user can check when it is settled. [1] http://lists.osmocom.org/pipermail/osmocom-sdr/2013-April/000584.html Thanks, Nuno Signed-off-by: Nuno Goncalves <nunojpg(a)gmail.com> diff --git a/src/rtl_test.c b/src/rtl_test.c index f5a56b8..c705e04 100644 --- a/src/rtl_test.c +++ b/src/rtl_test.c @@ -55,6 +55,8 @@ static int ppm_benchmark = 0; static int64_t ppm_count = 0L; static int64_t ppm_total = 0L; +static uint32_t samp_rate = DEFAULT_SAMPLE_RATE; + #ifndef _WIN32 static struct timespec ppm_start; static struct timespec ppm_recent; @@ -108,6 +110,7 @@ static void rtlsdr_callback(unsigned char *buf, uint32_t len, void *ctx) { uint32_t i, lost = 0; int64_t ns; + int real_rate; if (uninit) { bcnt = buf[0]; @@ -141,17 +144,23 @@ static void rtlsdr_callback(unsigned char *buf, uint32_t len, void *ctx) if (ppm_now.tv_sec - ppm_recent.tv_sec > PPM_DURATION) { ns = 1000000000L * (int64_t)(ppm_now.tv_sec - ppm_recent.tv_sec); ns += (int64_t)(ppm_now.tv_nsec - ppm_recent.tv_nsec); - printf("real sample rate: %i\n", + printf("real sample rate: %i", (int)((1000000000L * ppm_count / 2L) / ns)); - #ifndef __APPLE__ - clock_gettime(CLOCK_REALTIME, &ppm_recent); - #else - gettimeofday(&tv, NULL); - ppm_recent.tv_sec = tv.tv_sec; - ppm_recent.tv_nsec = tv.tv_usec*1000; - #endif + ppm_total += ppm_count / 2L; ppm_count = 0L; + + #ifndef _WIN32 + ns = 1000000000L * (int64_t)(ppm_now.tv_sec - ppm_start.tv_sec); + ns += (int64_t)(ppm_now.tv_nsec - ppm_start.tv_nsec); + real_rate = (int)(ppm_total * 1000000000L / ns); + printf(" cumulative PPM error: %.1f\n", + (1000000.0 * (real_rate - (int)samp_rate)) / samp_rate); + #else + printf("\n"); + #endif + + ppm_recent = ppm_now; } #endif } @@ -213,13 +222,10 @@ int main(int argc, char **argv) int sync_mode = 0; uint8_t *buffer; uint32_t dev_index = 0; - uint32_t samp_rate = DEFAULT_SAMPLE_RATE; uint32_t out_block_size = DEFAULT_BUF_LENGTH; int device_count; int count; int gains[100]; - int real_rate; - int64_t ns; while ((opt = getopt(argc, argv, "d:s:b:tpS::")) != -1) { switch (opt) { @@ -365,15 +371,6 @@ int main(int argc, char **argv) if (do_exit) { fprintf(stderr, "\nUser cancel, exiting...\n"); - if (ppm_benchmark) { -#ifndef _WIN32 - ns = 1000000000L * (int64_t)(ppm_recent.tv_sec - ppm_start.tv_sec); - ns += (int64_t)(ppm_recent.tv_nsec - ppm_start.tv_nsec); - real_rate = (int)(ppm_total * 1000000000L / ns); - printf("Cumulative PPM error: %i\n", - (int)round((double)(1000000 * (real_rate - (int)samp_rate)) / (double)samp_rate)); -#endif - } } else fprintf(stderr, "\nLibrary error %d, exiting...\n", r);

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osmocom-sdr November 2013