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lib: use FIR coefficients instead of magic + documentation

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Signed-off-by: Steve Markgraf <steve@steve-m.de>
This commit is contained in:
Jiri Pinkava 2013-09-22 14:01:12 +02:00 committed by Steve Markgraf
parent f17818f737
commit a42659602d
1 changed files with 56 additions and 10 deletions
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66
src/librtlsdr.c
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@ -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);