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convert.c
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convert.c
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// Part of dump1090, a Mode S message decoder for RTLSDR devices.
//
// convert.c: support for various IQ -> magnitude conversions
//
// Copyright (c) 2015 Oliver Jowett <[email protected]>
//
// This file is free software: you may copy, redistribute and/or modify it
// under the terms of the GNU General Public License as published by the
// Free Software Foundation, either version 2 of the License, or (at your
// option) any later version.
//
// This file is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.
#include "dump1090.h"
struct converter_state {
float dc_a;
float dc_b;
float z1_I;
float z1_Q;
};
static void convert_uc8_nodc(void *iq_data,
uint16_t *mag_data,
unsigned nsamples,
struct converter_state *state,
double *out_mean_level,
double *out_mean_power)
{
uint16_t *in = iq_data;
unsigned i;
uint64_t sum_level = 0;
uint64_t sum_power = 0;
uint16_t mag;
MODES_NOTUSED(state);
// unroll this a bit
for (i = 0; i < (nsamples>>3); ++i) {
mag = Modes.maglut[*in++];
*mag_data++ = mag;
sum_level += mag;
sum_power += (uint32_t)mag * (uint32_t)mag;
mag = Modes.maglut[*in++];
*mag_data++ = mag;
sum_level += mag;
sum_power += (uint32_t)mag * (uint32_t)mag;
mag = Modes.maglut[*in++];
*mag_data++ = mag;
sum_level += mag;
sum_power += (uint32_t)mag * (uint32_t)mag;
mag = Modes.maglut[*in++];
*mag_data++ = mag;
sum_level += mag;
sum_power += (uint32_t)mag * (uint32_t)mag;
mag = Modes.maglut[*in++];
*mag_data++ = mag;
sum_level += mag;
sum_power += (uint32_t)mag * (uint32_t)mag;
mag = Modes.maglut[*in++];
*mag_data++ = mag;
sum_level += mag;
sum_power += (uint32_t)mag * (uint32_t)mag;
mag = Modes.maglut[*in++];
*mag_data++ = mag;
sum_level += mag;
sum_power += (uint32_t)mag * (uint32_t)mag;
mag = Modes.maglut[*in++];
*mag_data++ = mag;
sum_level += mag;
sum_power += (uint32_t)mag * (uint32_t)mag;
}
for (i = 0; i < (nsamples&7); ++i) {
mag = Modes.maglut[*in++];
*mag_data++ = mag;
sum_level += mag;
sum_power += (uint32_t)mag * (uint32_t)mag;
}
if (out_mean_level) {
*out_mean_level = sum_level / 65536.0 / nsamples;
}
if (out_mean_power) {
*out_mean_power = sum_power / 65535.0 / 65535.0 / nsamples;
}
}
static void convert_uc8_generic(void *iq_data,
uint16_t *mag_data,
unsigned nsamples,
struct converter_state *state,
double *out_mean_level,
double *out_mean_power)
{
uint8_t *in = iq_data;
float z1_I = state->z1_I;
float z1_Q = state->z1_Q;
const float dc_a = state->dc_a;
const float dc_b = state->dc_b;
unsigned i;
uint8_t I, Q;
float fI, fQ, magsq;
float sum_level = 0, sum_power = 0;
for (i = 0; i < nsamples; ++i) {
I = *in++;
Q = *in++;
fI = (I - 127.5) / 127.5;
fQ = (Q - 127.5) / 127.5;
// DC block
z1_I = fI * dc_a + z1_I * dc_b;
z1_Q = fQ * dc_a + z1_Q * dc_b;
fI -= z1_I;
fQ -= z1_Q;
magsq = fI * fI + fQ * fQ;
if (magsq > 1)
magsq = 1;
float mag = sqrtf(magsq);
sum_power += magsq;
sum_level += mag;
*mag_data++ = (uint16_t)(mag * 65535.0 + 0.5);
}
state->z1_I = z1_I;
state->z1_Q = z1_Q;
if (out_mean_level) {
*out_mean_level = sum_level / nsamples;
}
if (out_mean_power) {
*out_mean_power = sum_power / nsamples;
}
}
static void convert_sc16_generic(void *iq_data,
uint16_t *mag_data,
unsigned nsamples,
struct converter_state *state,
double *out_mean_level,
double *out_mean_power)
{
uint16_t *in = iq_data;
float z1_I = state->z1_I;
float z1_Q = state->z1_Q;
const float dc_a = state->dc_a;
const float dc_b = state->dc_b;
unsigned i;
int16_t I, Q;
float fI, fQ, magsq;
float sum_level = 0, sum_power = 0;
for (i = 0; i < nsamples; ++i) {
I = (int16_t)le16toh(*in++);
Q = (int16_t)le16toh(*in++);
fI = I / 32768.0;
fQ = Q / 32768.0;
// DC block
z1_I = fI * dc_a + z1_I * dc_b;
z1_Q = fQ * dc_a + z1_Q * dc_b;
fI -= z1_I;
fQ -= z1_Q;
magsq = fI * fI + fQ * fQ;
if (magsq > 1)
magsq = 1;
float mag = sqrtf(magsq);
sum_power += magsq;
sum_level += mag;
*mag_data++ = (uint16_t)(mag * 65535.0 + 0.5);
}
state->z1_I = z1_I;
state->z1_Q = z1_Q;
if (out_mean_level) {
*out_mean_level = sum_level / nsamples;
}
if (out_mean_power) {
*out_mean_power = sum_power / nsamples;
}
}
static void convert_sc16q11_generic(void *iq_data,
uint16_t *mag_data,
unsigned nsamples,
struct converter_state *state,
double *out_mean_level,
double *out_mean_power)
{
uint16_t *in = iq_data;
float z1_I = state->z1_I;
float z1_Q = state->z1_Q;
const float dc_a = state->dc_a;
const float dc_b = state->dc_b;
unsigned i;
int16_t I, Q;
float fI, fQ, magsq;
float sum_level = 0, sum_power = 0;
for (i = 0; i < nsamples; ++i) {
I = (int16_t)le16toh(*in++);
Q = (int16_t)le16toh(*in++);
fI = I / 2048.0;
fQ = Q / 2048.0;
// DC block
z1_I = fI * dc_a + z1_I * dc_b;
z1_Q = fQ * dc_a + z1_Q * dc_b;
fI -= z1_I;
fQ -= z1_Q;
magsq = fI * fI + fQ * fQ;
if (magsq > 1)
magsq = 1;
float mag = sqrtf(magsq);
sum_power += magsq;
sum_level += mag;
*mag_data++ = (uint16_t)(sqrtf(magsq) * 65535.0 + 0.5);
}
state->z1_I = z1_I;
state->z1_Q = z1_Q;
if (out_mean_level) {
*out_mean_level = sum_level / nsamples;
}
if (out_mean_power) {
*out_mean_power = sum_power / nsamples;
}
}
static struct {
input_format_t format;
int can_filter_dc;
iq_convert_fn fn;
const char *description;
} converters_table[] = {
// In order of preference
{ INPUT_UC8, 0, convert_uc8_nodc, "UC8, integer/table path" },
{ INPUT_UC8, 1, convert_uc8_generic, "UC8, float path" },
{ INPUT_SC16, 1, convert_sc16_generic, "SC16, float path" },
{ INPUT_SC16Q11, 1, convert_sc16q11_generic, "SC16Q11, float path" },
{ 0, 0, NULL, NULL }
};
iq_convert_fn init_converter(input_format_t format,
double sample_rate,
int filter_dc,
struct converter_state **out_state)
{
int i;
for (i = 0; converters_table[i].fn; ++i) {
if (converters_table[i].format != format)
continue;
if (filter_dc && !converters_table[i].can_filter_dc)
continue;
break;
}
if (!converters_table[i].fn) {
fprintf(stderr, "no suitable converter for format=%d dc=%d\n",
format, filter_dc);
return NULL;
}
fprintf(stderr, "Using sample converter: %s\n", converters_table[i].description);
*out_state = malloc(sizeof(struct converter_state));
if (! *out_state) {
fprintf(stderr, "can't allocate converter state\n");
return NULL;
}
(*out_state)->z1_I = 0;
(*out_state)->z1_Q = 0;
if (filter_dc) {
// init DC block @ 1Hz
(*out_state)->dc_b = exp(-2.0 * M_PI * 1.0 / sample_rate);
(*out_state)->dc_a = 1.0 - (*out_state)->dc_b;
} else {
// if the converter does filtering, make sure it has no effect
(*out_state)->dc_b = 1.0;
(*out_state)->dc_a = 0.0;
}
return converters_table[i].fn;
}
void cleanup_converter(struct converter_state *state)
{
free(state);
}