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correct sample frequency with ppm offset

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Signed-off-by: Steve Markgraf <steve@steve-m.de>
This commit is contained in:
Steve Markgraf 2012-10-01 01:55:46 +02:00
parent 35263d0df3
commit a48f48e3b1
1 changed files with 25 additions and 16 deletions
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41
src/librtlsdr.c
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@ -584,6 +584,20 @@ int rtlsdr_set_if_freq(rtlsdr_dev_t *dev, uint32_t freq)
return r; return r;
} }
int rtlsdr_set_sample_freq_correction(rtlsdr_dev_t *dev, int ppm)
{
int r = 0;
uint8_t tmp;
int16_t offs = ppm * (-1) * TWO_POW(24) / 1000000;
tmp = offs & 0xff;
r |= rtlsdr_demod_write_reg(dev, 1, 0x3f, tmp, 1);
tmp = (offs >> 8) & 0x3f;
r |= rtlsdr_demod_write_reg(dev, 1, 0x3e, tmp, 1);
return r;
}
int rtlsdr_set_xtal_freq(rtlsdr_dev_t *dev, uint32_t rtl_freq, uint32_t tuner_freq) int rtlsdr_set_xtal_freq(rtlsdr_dev_t *dev, uint32_t rtl_freq, uint32_t tuner_freq)
{ {
int r = 0; int r = 0;
@ -721,13 +735,12 @@ int rtlsdr_set_freq_correction(rtlsdr_dev_t *dev, int ppm)
dev->corr = ppm; dev->corr = ppm;
r |= rtlsdr_set_sample_freq_correction(dev, ppm);
/* read corrected clock value into e4k structure */ /* read corrected clock value into e4k structure */
if (rtlsdr_get_xtal_freq(dev, NULL, &dev->e4k_s.vco.fosc)) if (rtlsdr_get_xtal_freq(dev, NULL, &dev->e4k_s.vco.fosc))
return -3; return -3;
#if 0
if (dev->rate) /* reset sample rate to apply new correction value */
r |= rtlsdr_set_sample_rate(dev, dev->rate);
#endif
if (dev->freq) /* retune to apply new correction value */ if (dev->freq) /* retune to apply new correction value */
r |= rtlsdr_set_center_freq(dev, dev->freq); r |= rtlsdr_set_center_freq(dev, dev->freq);
@ -863,6 +876,7 @@ int rtlsdr_set_tuner_gain_mode(rtlsdr_dev_t *dev, int mode)
int rtlsdr_set_sample_rate(rtlsdr_dev_t *dev, uint32_t samp_rate) int rtlsdr_set_sample_rate(rtlsdr_dev_t *dev, uint32_t samp_rate)
{ {
int r = 0;
uint16_t tmp; uint16_t tmp;
uint32_t rsamp_ratio; uint32_t rsamp_ratio;
double real_rate; double real_rate;
@ -874,14 +888,7 @@ int rtlsdr_set_sample_rate(rtlsdr_dev_t *dev, uint32_t samp_rate)
/* check for the maximum rate the resampler supports */ /* check for the maximum rate the resampler supports */
if (samp_rate > MAX_SAMP_RATE) if (samp_rate > MAX_SAMP_RATE)
samp_rate = MAX_SAMP_RATE; samp_rate = MAX_SAMP_RATE;
#if 0
/* read corrected clock value */
if (rtlsdr_get_xtal_freq(dev, &rtl_freq, NULL))
return -2;
if (samp_rate == MAX_SAMP_RATE && rtl_freq != DEF_RTL_XTAL_FREQ)
rtl_freq = DEF_RTL_XTAL_FREQ;
#endif
rsamp_ratio = (rtl_freq * TWO_POW(22)) / samp_rate; rsamp_ratio = (rtl_freq * TWO_POW(22)) / samp_rate;
rsamp_ratio &= ~3; rsamp_ratio &= ~3;
@ -899,15 +906,17 @@ int rtlsdr_set_sample_rate(rtlsdr_dev_t *dev, uint32_t samp_rate)
dev->rate = (uint32_t)real_rate; dev->rate = (uint32_t)real_rate;
tmp = (rsamp_ratio >> 16); tmp = (rsamp_ratio >> 16);
rtlsdr_demod_write_reg(dev, 1, 0x9f, tmp, 2); r |= rtlsdr_demod_write_reg(dev, 1, 0x9f, tmp, 2);
tmp = rsamp_ratio & 0xffff; tmp = rsamp_ratio & 0xffff;
rtlsdr_demod_write_reg(dev, 1, 0xa1, tmp, 2); r |= rtlsdr_demod_write_reg(dev, 1, 0xa1, tmp, 2);
r |= rtlsdr_set_sample_freq_correction(dev, dev->corr);
/* reset demod (bit 3, soft_rst) */ /* reset demod (bit 3, soft_rst) */
rtlsdr_demod_write_reg(dev, 1, 0x01, 0x14, 1); r |= rtlsdr_demod_write_reg(dev, 1, 0x01, 0x14, 1);
rtlsdr_demod_write_reg(dev, 1, 0x01, 0x10, 1); r |= rtlsdr_demod_write_reg(dev, 1, 0x01, 0x10, 1);
return 0; return r;
} }
uint32_t rtlsdr_get_sample_rate(rtlsdr_dev_t *dev) uint32_t rtlsdr_get_sample_rate(rtlsdr_dev_t *dev)