diff options
Diffstat (limited to 'src/librtlsdr.c')
| -rw-r--r-- | src/librtlsdr.c | 66 |
1 files changed, 56 insertions, 10 deletions
diff --git a/src/librtlsdr.c b/src/librtlsdr.c index 8537416..f08efd4 100644 --- a/src/librtlsdr.c +++ b/src/librtlsdr.c @@ -66,6 +66,26 @@ enum rtlsdr_async_status { RTLSDR_RUNNING }; +#define FIR_LEN 16 + +/* + * FIR coefficients. + * + * The filter is running at XTal frequency. It is symmetric filter with 32 + * coefficients. Only first 16 coefficients are specified, the other 16 + * use the same values but in reversed order. The first coefficient in + * the array is the outer one, the last, the last is the inner one. + * First 8 coefficients are 8 bit signed integers, the next 8 coefficients + * are 12 bit signed integers. All coefficients have the same weight. + * + * Default FIR coefficients used for DAB/FM by the Windows driver, + * the DVB driver uses different ones + */ +static const int fir_default[FIR_LEN] = { + -54, -36, -41, -40, -32, -14, 14, 53, /* 8 bit signed */ + 101, 156, 215, 273, 327, 372, 404, 421 /* 12 bit signed */ +}; + struct rtlsdr_dev { libusb_context *ctx; struct libusb_device_handle *devh; @@ -79,6 +99,7 @@ struct rtlsdr_dev { /* rtl demod context */ uint32_t rate; /* Hz */ uint32_t rtl_xtal; /* Hz */ + int fir[FIR_LEN]; int direct_sampling; /* tuner context */ enum rtlsdr_tuner tuner_type; @@ -532,17 +553,43 @@ void rtlsdr_set_i2c_repeater(rtlsdr_dev_t *dev, int on) rtlsdr_demod_write_reg(dev, 1, 0x01, on ? 0x18 : 0x10, 1); } +int rtlsdr_set_fir(rtlsdr_dev_t *dev) +{ + uint8_t fir[20]; + + int i; + /* format: int8_t[8] */ + for (i = 0; i < 8; ++i) { + const int val = dev->fir[i]; + if (val < -128 || val > 127) { + return -1; + } + fir[i] = val; + } + /* format: int12_t[8] */ + for (i = 0; i < 8; i += 2) { + const int val0 = dev->fir[8+i]; + const int val1 = dev->fir[8+i+1]; + if (val0 < -2048 || val0 > 2047 || val1 < -2048 || val1 > 2047) { + return -1; + } + fir[8+i*3/2] = val0 >> 4; + fir[8+i*3/2+1] = (val0 << 4) | ((val1 >> 8) & 0x0f); + fir[8+i*3/2+2] = val1; + } + + for (i = 0; i < (int)sizeof(fir); i++) { + if (rtlsdr_demod_write_reg(dev, 1, 0x1c + i, fir[i], 1)) + return -1; + } + + return 0; +} + void rtlsdr_init_baseband(rtlsdr_dev_t *dev) { unsigned int i; - /* default FIR coefficients used for DAB/FM by the Windows driver, - * the DVB driver uses different ones */ - const uint8_t fir_coeff[] = { - 0xca, 0xdc, 0xd7, 0xd8, 0xe0, 0xf2, 0x0e, 0x35, 0x06, 0x50, - 0x9c, 0x0d, 0x71, 0x11, 0x14, 0x71, 0x74, 0x19, 0x41, 0xa5, - }; - /* initialize USB */ rtlsdr_write_reg(dev, USBB, USB_SYSCTL, 0x09, 1); rtlsdr_write_reg(dev, USBB, USB_EPA_MAXPKT, 0x0002, 2); @@ -564,9 +611,7 @@ void rtlsdr_init_baseband(rtlsdr_dev_t *dev) for (i = 0; i < 6; i++) rtlsdr_demod_write_reg(dev, 1, 0x16 + i, 0x00, 1); - /* set FIR coefficients */ - for (i = 0; i < sizeof (fir_coeff); i++) - rtlsdr_demod_write_reg(dev, 1, 0x1c + i, fir_coeff[i], 1); + rtlsdr_set_fir(dev); /* enable SDR mode, disable DAGC (bit 5) */ rtlsdr_demod_write_reg(dev, 0, 0x19, 0x05, 1); @@ -1344,6 +1389,7 @@ int rtlsdr_open(rtlsdr_dev_t **out_dev, uint32_t index) return -ENOMEM; memset(dev, 0, sizeof(rtlsdr_dev_t)); + memcpy(dev->fir, fir_default, sizeof(fir_default)); libusb_init(&dev->ctx); |