Port from librtlsdr to SoapySDR API (rtl_fm, rtl_sdr, and rtl_power) #1
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Current status: able to list devices, open, set some settings, but cannot yet receive samples. librtlsdr has an rtlsdr_read_async API with a callback, data as pairs of unsigned 8-bit values, SoapySDR has streams, and can read in a variety of formats (SOAPY_SDR_U8 for compatibility), not yet working, some impedance mismatches, but not by much. Crashes in buffer handling: |
…nd Q) invalid format 'U8' -- Only CS8, CS16 and CF32 are supported by SoapyRTLSDR module
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Some progress, there is now stream output, but when played through When piped through to sox to convert to wav: ./rtl_fm -M wbfm -f 107.1M | sox -r 32k -t raw -e s -b 16 -c 1 -V1 - -t wav /tmp/a.wavit is a solid buzzing sound: https://soundcloud.com/user-223812058/rtl-fm-fail-1 Audacity plot spectrum shows:
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Slight problem: SoapyRTLSDR reports native format as SOAPY_SDR_CS8 (complex signed 8-bit pairs), but is actually CU8 (unsigned), the driver actually subtracts 127 https://github.com/pothosware/SoapyRTLSDR/blob/a44abc3f1ac2c62d707902551f1c2c1e70551c84/Streaming.cpp#L372-L391 - although the direct stream access API uses CU8, see pothosware/SoapyRTLSDR#15. But even then, something seems wrong with the samples: actually not necessarily, rtlsdr_callback first thing does: unnecessary conversions (-127 in SoapyRTLSDR, +127 in rtl_fm dongle_thread_fn, then -127 in rtl_fm rtlsdr_callback!) but now fixing the buffer types, get choppy static |
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It may be more straightforward to port rtl_sdr first, since it outputs raw I/Q samples, without the complexity of FM demodulation to debug. Pushed what I have so far, but quite broken, curiously readStream returns 8192 bytes but all bytes are 00 or 01(?), not sure what is happening here. |
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Turning up the gain (-g 40 with rtl_sdr) gives more interesting results: at a lower gain, 00 and 01 similar to 7f and 80 (signed/unsigned offset) with librtlsdr rtl_sdr. However, with no gain specified, librtlsdr rtl_sdr works as expected, but this branch rtl_sdr only shows 00/01's. Auto-gain is not set, in src/convenience/convenience.c verbose_auto_gain (and verbose_gain_set), couldn't find an equivalent for rtlsdr_set_tuner_gain_mode(dev, 0); (= set auto gain) and rtlsdr_set_tuner_gain_mode(dev, 1); (= set manual gain). Not called in SoapyRTLSDR: https://github.com/pothosware/SoapyRTLSDR/search?utf8=✓&q=rtlsdr_set_tuner_gain_mode - so for now, will need to set gain explicitly (or hardcode a reasonable default?). update: filed pothosware/SoapyRTLSDR#21 Automatic gain mode setting, rtlsdr_set_tuner_gain_mode(dev, 0) equivalent |
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With gain, something can now be heard, just barely: but it is still choppy (the rtl_fm stream starts and stops). Recording to a .wav file on disk with sox (therefore removing the gaps): https://soundcloud.com/user-223812058/rtl-fm-progress-1 it sounds noisy but also as if it was sped up. Halving the sample rate ( Another potential problem: setting the bandwidth? "Bandwidth set to automatic resulted in 0 Hz." vs expected "Bandwidth set to automatic resulted in 350000 Hz.". verbose_set_bandwidth uses rtlsdr_set_and_get_tuner_bandwidth, to both set and get the bandwidth. 0 indicates "automatic", meaning equal to the sampling rate ( Setting bandwidth is relatively "new", rtlsdr_set_tuner_bandwidth was added in librtlsdr/librtlsdr@92df068 Mar 17, 2015 see http://lists.osmocom.org/pipermail/osmocom-sdr/2015-June/000077.html. Other projects have ran into problems relying on this function - jpoirier/gortlsdr#14 - since it "is not present in Linux distro releases of rtl-sdr package" (Feb 28). There was a post to osmocom-sdr requesting a new official librtlsdr release: http://lists.osmocom.org/pipermail/osmocom-sdr/2016-February/001373.html but meanwhile "A project I've been using this package in simply requires users to build rtlsdr from source" hmm.. may be premature to update SoapyRTLSDR setBandwidth to call rtlsdr_set_tuner_bandwidth(). Either way, not likely the problem here. update: filed pothosware/SoapyRTLSDR#20 setBandwidth/getBandwidth no-ops, should call rtlsdr_set_and_get_tuner_bandwidth? Possibly has to do with rtlsdr_read_async: - rtl_sdr has a sync mode, but rtl_fm is only async, calls the callback, when porting I replaced with SoapySDRDevice_readStream, sync. There is significant logic in librtlsdr to buffer async, and then call the callback when appropriate: https://github.com/librtlsdr/librtlsdr/blob/development/src/librtlsdr.c#L1840 - although SoapyRTLSDR https://github.com/pothosware/SoapyRTLSDR/blob/master/Streaming.cpp does call rtlsdr_read_async under the hood. What parameters are there to adjust how fast I can read from the SDR, via SoapySDR? ... There is a "buflen" kwarg argument for setupStream in SoapyRTLSDR, but it defaults to 16384, same as DEFAULT_BUF_LENGTH in rtl_fm (but rtl_sdr has 16 * 16384), changing no effect, still reads 8192. The original rtl_fm's rtlsdr_callback gets called consistently with len=262144 (= 16384 * 16). |
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Turned out to be a simple problem, readStream returns the number of elements read, aka the number of samples, which consist of both I and Q values, each 8-bit, forming a complex number. |
Instead of having rtl_fm and rtl_sdr convert CS8 to CU8, add the read_samples_cu8() convenience function. This reads from SoapySDR using CS8 format, and adds 127 to convert to CU8, the actual native format - a redundant but necessary conversion, could be improved after pothosware/SoapyRTLSDR#15 if SoapyRTLSDR adds native CU8 support (remove the loop in read_samples_cu8()).
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rtl_fm and rtl_sdr basically work now (rtl_power potentially as well but needs more longer-term testing), with an RTL-SDR. Not compatible with a bladeRF yet due to higher bit-rate #8. With a HackRF, rtl_sdr emits output, but only silence (0x7f - 0x83), need to adjust the multiple gains? SoapyHackRF::setGain https://github.com/pothosware/SoapyHackRF/blob/master/HackRF_Settings.cpp#L358 has some.. interesting logic, to set a AMP, VGA, and LNA (comments mine): if ( gain <= 0 )
{
_rx_stream->lna_gain = 0;
_rx_stream->vga_gain = 0;
_current_amp = 0;
}else if ( gain <= /*51*/ (HACKRF_RX_LNA_MAX_DB / 2) + (HACKRF_RX_VGA_MAX_DB / 2) )
{
_rx_stream->vga_gain = (gain / 3) & ~0x1;
_rx_stream->lna_gain = gain - _rx_stream->vga_gain;
_current_amp = 0;
}else if ( gain <= /*65*/ ( (HACKRF_RX_LNA_MAX_DB / 2) + (HACKRF_RX_VGA_MAX_DB / 2) + HACKRF_AMP_MAX_DB) )
{
_current_amp = HACKRF_AMP_MAX_DB;
_rx_stream->vga_gain = ( (gain - _current_amp) / 3) & ~0x1;
_rx_stream->lna_gain = gain -_current_amp - _rx_stream->vga_gain;
}else if ( gain <= /*116*/ HACKRF_RX_LNA_MAX_DB + HACKRF_RX_VGA_MAX_DB + HACKRF_AMP_MAX_DB )
{
_current_amp = HACKRF_AMP_MAX_DB;
_rx_stream->vga_gain = (gain - _current_amp) * double(HACKRF_RX_LNA_MAX_DB) / double(HACKRF_RX_VGA_MAX_DB);
_rx_stream->lna_gain = gain - _current_amp - _rx_stream->vga_gain;
}
_rx_stream->amp_gain=_current_amp;
ret = hackrf_set_lna_gain( _dev, _rx_stream->lna_gain );
ret |= hackrf_set_vga_gain( _dev, _rx_stream->vga_gain );
ret |= hackrf_set_amp_enable( _dev, (_current_amp > 0) ? 1 : 0 );and in the headers: #define HACKRF_RX_VGA_MAX_DB 62
#define HACKRF_TX_VGA_MAX_DB 47
#define HACKRF_RX_LNA_MAX_DB 40
#define HACKRF_AMP_MAX_DB 14setGain(40) results in LNA=28, VGA=12, AMP=0 (from adding logging to SoapyHackRF), which I can copy in CubicSDR. Seeing strange return values from readStream with the HackRF: then it stops. Why the error? -1 is SOAPY_SDR_TIMEOUT, fixed by increasing timeout, but only hear static with the HackRF. readStream ret=131072 (=16384 * 8) Setting bandwidth and sampling rate 20e6, no difference. SoapySDRUtil --probe shows: with -g 116, I can sometimes sort of hear something above the static with the HackRF, even though it logs invalid parameter: HackRF device setting gains: LNA=36, VGA=63, AMP=14 |
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Merged what I have so far since it works well with rtlsdr driver, new issue for HackRF: #9 |
Port to use the vendor-neutral SoapySDR library instead, see https://github.com/pothosware/SoapySDR/wiki
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