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lib: check for validity of sample rates

Browse Source 
Thanks to Joris van Rantwijk for finding what seems to be
a hardware limitation/bug (bit 28 of the rsamp register being
forced to the value of bit 27).

Signed-off-by: Steve Markgraf <steve@steve-m.de>
This commit is contained in:
Steve Markgraf 2014-01-05 22:51:44 +01:00
parent d683b128f9
commit 003bd51167
2 changed files with 21 additions and 9 deletions
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12
include/rtl-sdr.h
View File

@ -243,7 +243,17 @@ RTLSDR_API int rtlsdr_set_tuner_if_gain(rtlsdr_dev_t *dev, int stage, int gain);
*/
RTLSDR_API int rtlsdr_set_tuner_gain_mode(rtlsdr_dev_t *dev, int manual);
/* this will select the baseband filters according to the requested sample rate */
/*!
* Set the sample rate for the device, also selects the baseband filters
* according to the requested sample rate for tuners where this is possible.
*
* \param dev the device handle given by rtlsdr_open()
* \param samp_rate the sample rate to be set, possible values are:
* 225001 - 300000 Hz
* 900001 - 3200000 Hz
* sample loss is to be expected for rates > 2400000
* \return 0 on success, -EINVAL on invalid rate
*/
RTLSDR_API int rtlsdr_set_sample_rate(rtlsdr_dev_t *dev, uint32_t rate);
/*!

18
src/librtlsdr.c
View File

@ -337,8 +337,6 @@ static rtlsdr_dongle_t known_devices[] = {
#define MIN_RTL_XTAL_FREQ (DEF_RTL_XTAL_FREQ - 1000)
#define MAX_RTL_XTAL_FREQ (DEF_RTL_XTAL_FREQ + 1000)
#define MAX_SAMP_RATE 3200000
#define CTRL_IN (LIBUSB_REQUEST_TYPE_VENDOR | LIBUSB_ENDPOINT_IN)
#define CTRL_OUT (LIBUSB_REQUEST_TYPE_VENDOR | LIBUSB_ENDPOINT_OUT)
#define CTRL_TIMEOUT 300
@ -1053,20 +1051,24 @@ int rtlsdr_set_sample_rate(rtlsdr_dev_t *dev, uint32_t samp_rate)
{
int r = 0;
uint16_t tmp;
uint32_t rsamp_ratio;
uint32_t rsamp_ratio, real_rsamp_ratio;
double real_rate;
if (!dev)
return -1;
/* check for the maximum rate the resampler supports */
if (samp_rate > MAX_SAMP_RATE)
samp_rate = MAX_SAMP_RATE;
/* check if the rate is supported by the resampler */
if ((samp_rate <= 225000) || (samp_rate > 3200000) ||
((samp_rate > 300000) && (samp_rate <= 900000))) {
fprintf(stderr, "Invalid sample rate: %u Hz\n", samp_rate);
return -EINVAL;
}
rsamp_ratio = (dev->rtl_xtal * TWO_POW(22)) / samp_rate;
rsamp_ratio &= ~3;
rsamp_ratio &= 0x0ffffffc;
real_rate = (dev->rtl_xtal * TWO_POW(22)) / rsamp_ratio;
real_rsamp_ratio = rsamp_ratio | ((rsamp_ratio & 0x08000000) << 1);
real_rate = (dev->rtl_xtal * TWO_POW(22)) / real_rsamp_ratio;
if ( ((double)samp_rate) != real_rate )
fprintf(stderr, "Exact sample rate is: %f Hz\n", real_rate);