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authorJiri Pinkava <j-pi@seznam.cz>2013-09-22 14:01:12 +0200
committerSteve Markgraf <steve@steve-m.de>2013-12-02 01:31:14 +0100
commita42659602deff728da6731928e660f90407bbbe0 (patch)
tree9a5563dbc6ccb5cd6d353b40c0749153f9763b6d
parentf17818f7370e166d367c2f33d2b6fc1e22f48e6b (diff)
lib: use FIR coefficients instead of magic + documentation
Signed-off-by: Steve Markgraf <steve@steve-m.de>
-rw-r--r--src/librtlsdr.c66
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);