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mayhem-firmware/firmware/baseband/dsp_frequency_xlator.hpp
T
Oleg Belousov b048b8f4f1 Feature/sliding freq (#3280) 
* Add sliding-frequency audio receiver tuning
* Move ADS-B receiver to external app
* Move AIS receiver to external app
* Move APRS receiver to external app
* Move APRS transmitter to external app
* Isolate filtered spectrum collection from WFM
* Fixed the issues #3280
* fpga_bridge.c: init registers per reference fpga_init, add quarter-shift mode setter
* radio.hpp: expose cached FPGA quarter-rate shift
* radio.cpp: program FPGA quarter-rate shift together with tuning offset
* tuning.hpp: pass AFE rate and direction to tuning config, add quarter_shift field
* tuning.cpp: import full PRALINE RX/TX tuning tables with quarter-shift offsets
* clock_manager: stop writing bogus RX digital gain, keep quarter shift across rate changes
* receiver_model: port LPF bandwidth from reference auto_bandwidth, use cached quarter shift
* adsb_rx: enable RF amp by default on first run
* ui_geomap.hpp: add hemisphere fields, degrees become magnitude
* ui_geomap: use hemisphere selector for lat/lon sign, fix minute/second wrap carry
* ui_menu: guard select against empty menu
* waterfall_designer: header updates for profile file handling
* waterfall_designer: exception-free profile parsing, CRLF handling, deferred nav callbacks, backup cleanup
* external.ld: scope app section globs to their own object directories
* CMakeLists: relink when external.ld changes
* tools: add external app symbol placement checker
* tools: add guru meditation address lookup script
* tools: add per-function stack usage report script
Co-authored-by: gullradriel <gullradriel@users.noreply.github.com>
2026-08-08 21:47:54 +02:00

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/*
* Copyright (C) 2026
*
* This file is part of PortaPack.
*/
#ifndef __DSP_FREQUENCY_XLATOR_H__
#define __DSP_FREQUENCY_XLATOR_H__
#include "dsp_decimate.hpp"
#include "dsp_types.hpp"
#include <array>
#include <cstdint>
namespace dsp {
/* Fixed-point complex mixer for the Audio RX channelizer. */
class FrequencyTranslator {
public:
FrequencyTranslator() {
for (size_t i = 0; i < oscillator_q15_.size(); ++i) {
oscillator_q15_[i] =
static_cast<uint16_t>(sine_q15_[static_cast<uint8_t>(i + 64)]) |
(static_cast<uint32_t>(
static_cast<uint16_t>(sine_q15_[i]))
<< 16);
}
}
void set_sample_rate(const uint32_t sampling_rate) {
sampling_rate_ = sampling_rate;
update_phase_increment();
}
void set_frequency(const int32_t frequency) {
frequency_ = frequency;
update_phase_increment();
}
buffer_c16_t execute(const buffer_c16_t& src, const buffer_c16_t& dst) {
auto phase = phase_;
for (size_t i = 0; i < src.count; ++i) {
const uint8_t index = phase >> 24;
const uint8_t next = index + 1;
const int32_t fraction = (phase >> 16) & 0xff;
const uint32_t oscillator_first = oscillator_q15_[index];
const uint32_t oscillator_next = oscillator_q15_[next];
const int32_t sine_first =
static_cast<int16_t>(oscillator_first >> 16);
const int32_t cosine_first =
static_cast<int16_t>(oscillator_first);
const int32_t sine =
sine_first +
(((static_cast<int16_t>(oscillator_next >> 16) -
sine_first) *
fraction) >>
8);
const int32_t cosine =
cosine_first +
(((static_cast<int16_t>(oscillator_next) -
cosine_first) *
fraction) >>
8);
const uint32_t oscillator =
static_cast<uint16_t>(cosine) |
(static_cast<uint32_t>(
static_cast<uint16_t>(sine))
<< 16);
const uint32_t sample =
*reinterpret_cast<const uint32_t*>(&src.p[i]);
/* Two packed dual-16-bit multiplies implement
* (I+jQ) * (cos-j sin). */
const int32_t out_i =
rounded_shift(__SMUAD(sample, oscillator), 15);
const int32_t out_q =
rounded_shift(__SMUSDX(oscillator, sample), 15);
*reinterpret_cast<uint32_t*>(&dst.p[i]) =
__PKHBT(__SSAT(out_i, 16), __SSAT(out_q, 16), 16);
phase += phase_increment_;
}
phase_ = phase;
return {dst.p, src.count, src.sampling_rate};
}
private:
friend class FrequencyTranslatingDecimator32By8;
static constexpr int32_t rounded_shift(
const int32_t value,
const uint32_t bits) {
const int32_t rounding = int32_t{1} << (bits - 1);
return value >= 0
? (value + rounding) >> bits
: -((-value + rounding) >> bits);
}
void update_phase_increment() {
if (sampling_rate_) {
phase_increment_ = static_cast<uint32_t>(
(static_cast<int64_t>(frequency_) * (int64_t{1} << 32)) /
sampling_rate_);
}
}
static constexpr std::array<int16_t, 256> sine_q15_{{
0,
804,
1608,
2410,
3212,
4011,
4808,
5602,
6393,
7179,
7962,
8739,
9512,
10278,
11039,
11793,
12539,
13279,
14010,
14732,
15446,
16151,
16846,
17530,
18204,
18868,
19519,
20159,
20787,
21403,
22005,
22594,
23170,
23731,
24279,
24811,
25329,
25832,
26319,
26790,
27245,
27683,
28105,
28510,
28898,
29268,
29621,
29956,
30273,
30571,
30852,
31113,
31356,
31580,
31785,
31971,
32137,
32285,
32412,
32521,
32609,
32678,
32728,
32757,
32767,
32757,
32728,
32678,
32609,
32521,
32412,
32285,
32137,
31971,
31785,
31580,
31356,
31113,
30852,
30571,
30273,
29956,
29621,
29268,
28898,
28510,
28105,
27683,
27245,
26790,
26319,
25832,
25329,
24811,
24279,
23731,
23170,
22594,
22005,
21403,
20787,
20159,
19519,
18868,
18204,
17530,
16846,
16151,
15446,
14732,
14010,
13279,
12539,
11793,
11039,
10278,
9512,
8739,
7962,
7179,
6393,
5602,
4808,
4011,
3212,
2410,
1608,
804,
0,
-804,
-1608,
-2410,
-3212,
-4011,
-4808,
-5602,
-6393,
-7179,
-7962,
-8739,
-9512,
-10278,
-11039,
-11793,
-12539,
-13279,
-14010,
-14732,
-15446,
-16151,
-16846,
-17530,
-18204,
-18868,
-19519,
-20159,
-20787,
-21403,
-22005,
-22594,
-23170,
-23731,
-24279,
-24811,
-25329,
-25832,
-26319,
-26790,
-27245,
-27683,
-28105,
-28510,
-28898,
-29268,
-29621,
-29956,
-30273,
-30571,
-30852,
-31113,
-31356,
-31580,
-31785,
-31971,
-32137,
-32285,
-32412,
-32521,
-32609,
-32678,
-32728,
-32757,
-32767,
-32757,
-32728,
-32678,
-32609,
-32521,
-32412,
-32285,
-32137,
-31971,
-31785,
-31580,
-31356,
-31113,
-30852,
-30571,
-30273,
-29956,
-29621,
-29268,
-28898,
-28510,
-28105,
-27683,
-27245,
-26790,
-26319,
-25832,
-25329,
-24811,
-24279,
-23731,
-23170,
-22594,
-22005,
-21403,
-20787,
-20159,
-19519,
-18868,
-18204,
-17530,
-16846,
-16151,
-15446,
-14732,
-14010,
-13279,
-12539,
-11793,
-11039,
-10278,
-9512,
-8739,
-7962,
-7179,
-6393,
-5602,
-4808,
-4011,
-3212,
-2410,
-1608,
-804,
}};
std::array<uint32_t, 256> oscillator_q15_{};
uint32_t phase_{0};
uint32_t phase_increment_{0};
uint32_t sampling_rate_{192000};
int32_t frequency_{0};
};
/*
* Frequency-translating 32-tap FIR decimator. Frequency translation is
* split between coefficients modulated when tuning changes and a cheap
* output-rate phase rotation. This avoids running an NCO at the 384kHz
* input rate.
*/
class FrequencyTranslatingDecimator32By8 {
public:
static constexpr size_t decimation_factor = 8;
static constexpr size_t taps_count = 32;
void configure(
const std::array<int16_t, taps_count>& taps,
const uint32_t input_sampling_rate) {
taps_ = taps;
input_sampling_rate_ = input_sampling_rate;
decimator_.configure(complex_taps_, decimation_factor);
output_xlator_.set_sample_rate(input_sampling_rate / decimation_factor);
update_taps();
}
void set_frequency(const int32_t frequency) {
frequency_ = frequency;
output_xlator_.set_frequency(frequency);
update_taps();
}
buffer_c16_t execute(
const buffer_c16_t& src,
const buffer_c16_t& dst) {
const auto filtered = decimator_.execute(src, dst);
return output_xlator_.execute(filtered, dst);
}
private:
static void oscillator(
const uint32_t phase,
int32_t& sine,
int32_t& cosine) {
const uint8_t index = phase >> 24;
const uint8_t next = index + 1;
const uint8_t cosine_index = index + 64;
const uint8_t cosine_next = cosine_index + 1;
const int32_t fraction = (phase >> 16) & 0xff;
const int32_t sine_first = FrequencyTranslator::sine_q15_[index];
const int32_t cosine_first = FrequencyTranslator::sine_q15_[cosine_index];
sine = sine_first +
(((FrequencyTranslator::sine_q15_[next] - sine_first) * fraction) >> 8);
cosine = cosine_first +
(((FrequencyTranslator::sine_q15_[cosine_next] - cosine_first) * fraction) >> 8);
}
void update_taps() {
if (!input_sampling_rate_)
return;
const uint32_t tap_phase_increment = static_cast<uint32_t>(
(static_cast<int64_t>(frequency_) * (int64_t{1} << 32)) /
input_sampling_rate_);
/* Centre the modulation on the FIR midpoint. Besides changing
* only a constant output phase, this makes the two coefficients
* in each symmetric pair complex conjugates. That property is
* important after quantization: starting at tap zero accumulated
* a one-sided phase and rounding error across the whole filter. */
uint32_t phase = static_cast<uint32_t>(
-((static_cast<int64_t>(
static_cast<int32_t>(tap_phase_increment)) *
static_cast<int64_t>(taps_count - 1)) /
2));
for (size_t i = 0; i < taps_count; ++i) {
int32_t sine;
int32_t cosine;
oscillator(phase, sine, cosine);
/* FIRAndDecimateComplex uses Q16 coefficients; the source
* real-tap filters use Q15 coefficients. */
const int32_t tap = taps_[i];
complex_taps_[i] = {
static_cast<int16_t>(
FrequencyTranslator::rounded_shift(
tap * cosine, 14)),
static_cast<int16_t>(
FrequencyTranslator::rounded_shift(
tap * sine, 14))};
phase += tap_phase_increment;
}
decimator_.set_taps(complex_taps_);
}
std::array<int16_t, taps_count> taps_{};
std::array<complex16_t, taps_count> complex_taps_{};
decimate::FIRAndDecimateComplex decimator_{};
FrequencyTranslator output_xlator_{};
uint32_t input_sampling_rate_{0};
int32_t frequency_{0};
};
} /* namespace dsp */
#endif /*__DSP_FREQUENCY_XLATOR_H__*/
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