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SoftFM
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Be accurate in disallowing sampling rates in SoftFM. 

The rtl-sdr driver code disallows most of the sampling rates below
900 kS/s. However, it allows a small window of sampling rates
between [250001, 300000]. The update to the conditional is along
the lines of the conditions imposed by the RTL SDR driver here:

http://cgit.osmocom.org/rtl-sdr/tree/src/librtlsdr.c

The default sampling rate of 1 MS/s causes severe buffer underruns on
a Raspberry Pi 2. However choosing a sampling rate of 250 kS/s and
lower values for PCM sampling causes successful FM demodulation of
strong FM stations on the device.
This commit is contained in:
Divye Kapoor 2015-11-21 07:57:47 +00:00
parent fc30717198
commit e9fe05c4ea
1 changed files with 7 additions and 4 deletions
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11
main.cc
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@ -144,7 +144,7 @@ void adjust_gain(SampleVector& samples, double gain)
* This code runs in a separate thread. * This code runs in a separate thread.
* The RTL-SDR library is not capable of buffering large amounts of data. * The RTL-SDR library is not capable of buffering large amounts of data.
* Running this in a background thread ensures that the time between calls * Running this in a background thread ensures that the time between calls
* to RtlSdrSource::get_samples() is very short. * to RtlSdrSource::get_samples() is very short.
*/ */
void read_source_data(RtlSdrSource *rtlsdr, DataBuffer<IQSample> *buf) void read_source_data(RtlSdrSource *rtlsdr, DataBuffer<IQSample> *buf)
{ {
@ -219,7 +219,7 @@ void usage()
" -d devidx RTL-SDR device index, 'list' to show device list (default 0)\n" " -d devidx RTL-SDR device index, 'list' to show device list (default 0)\n"
" -g gain Set LNA gain in dB, or 'auto' (default auto)\n" " -g gain Set LNA gain in dB, or 'auto' (default auto)\n"
" -a Enable RTL AGC mode (default disabled)\n" " -a Enable RTL AGC mode (default disabled)\n"
" -s ifrate IF sample rate in Hz (default 1000000, min 900001)\n" " -s ifrate IF sample rate in Hz (default 1000000, valid range: [225001, 300000] U [900000, 3200000])\n"
" -r pcmrate Audio sample rate in Hz (default 48000 Hz)\n" " -r pcmrate Audio sample rate in Hz (default 48000 Hz)\n"
" -M Disable stereo decoding\n" " -M Disable stereo decoding\n"
" -R filename Write audio data as raw S16_LE samples\n" " -R filename Write audio data as raw S16_LE samples\n"
@ -355,8 +355,11 @@ int main(int argc, char **argv)
} }
break; break;
case 's': case 's':
// NOTE: RTL does not suppor sample rate 900 kS/s or lower // NOTE: RTL does not support some sample rates below 900 kS/s
if (!parse_dbl(optarg, ifrate) || ifrate <= 900000) { // Also, max sampling rate is 3.2 MS/s
if (!parse_dbl(optarg, ifrate) ||
(ifrate <= 225000) || (ifrate > 3200000) ||
((ifrate > 300000) && (ifrate <= 900000))) {
badarg("-s"); badarg("-s");
} }
break; break;