mayhem-firmware/firmware/baseband/dsp_demodulate.cpp

/*
 * Copyright (C) 2014 Jared Boone, ShareBrained Technology, Inc.
 *
 * This file is part of PortaPack.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * This program 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; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.
 */

#include "dsp_demodulate.hpp"

#include "complex.hpp"
#include "fxpt_atan2.hpp"
#include "utility_m4.hpp"

#include <hal.h>

namespace dsp {
namespace demodulate {

buffer_f32_t AM::execute(
    const buffer_c16_t& src,
    const buffer_f32_t& dst) {
    const void* src_p = src.p;
    const auto src_end = &src.p[src.count];
    auto dst_p = dst.p;
    while (src_p < src_end) {
        const uint32_t sample0 = *__SIMD32(src_p)++;
        const uint32_t sample1 = *__SIMD32(src_p)++;
        const uint32_t mag_sq0 = __SMUAD(sample0, sample0);
        const uint32_t mag_sq1 = __SMUAD(sample1, sample1);
        *(dst_p++) = __builtin_sqrtf(mag_sq0) * k;
        *(dst_p++) = __builtin_sqrtf(mag_sq1) * k;
    }

    return {dst.p, src.count, src.sampling_rate};
}

buffer_f32_t SSB::execute(
    const buffer_c16_t& src,
    const buffer_f32_t& dst) {
    const complex16_t* src_p = src.p;
    const auto src_end = &src.p[src.count];
    auto dst_p = dst.p;
    while (src_p < src_end) {
        *(dst_p++) = (src_p++)->real() * k;
        *(dst_p++) = (src_p++)->real() * k;
        *(dst_p++) = (src_p++)->real() * k;
        *(dst_p++) = (src_p++)->real() * k;
    }

    return {dst.p, src.count, src.sampling_rate};
}
/*
static inline float angle_approx_4deg0(const complex32_t t) {
        const auto x = static_cast<float>(t.imag()) / static_cast<float>(t.real());
        return 16384.0f * x;
}
*/
static inline float angle_approx_0deg27(const complex32_t t) {
    if (t.real()) {
        const auto x = static_cast<float>(t.imag()) / static_cast<float>(t.real());
        return x / (1.0f + 0.28086f * x * x);
    } else {
        return (t.imag() < 0) ? -1.5707963268f : 1.5707963268f;
    }
}

static inline float angle_precise(const complex32_t t) {
    return atan2f(t.imag(), t.real());
}

buffer_f32_t FM::execute(
    const buffer_c16_t& src,
    const buffer_f32_t& dst) {
    auto z = z_;

    const void* src_p = src.p;
    const auto src_end = &src.p[src.count];
    auto dst_p = dst.p;
    while (src_p < src_end) {
        const auto s0 = *__SIMD32(src_p)++;
        const auto s1 = *__SIMD32(src_p)++;
        const auto t0 = multiply_conjugate_s16_s32(s0, z);
        const auto t1 = multiply_conjugate_s16_s32(s1, s0);
        z = s1;
        *(dst_p++) = angle_precise(t0) * kf;
        *(dst_p++) = angle_precise(t1) * kf;
    }
    z_ = z;

    return {dst.p, src.count, src.sampling_rate};
}

buffer_s16_t FM::execute(
    const buffer_c16_t& src,
    const buffer_s16_t& dst) {
    auto z = z_;

    const void* src_p = src.p;
    const auto src_end = &src.p[src.count];
    void* dst_p = dst.p;
    while (src_p < src_end) {
        const auto s0 = *__SIMD32(src_p)++;
        const auto s1 = *__SIMD32(src_p)++;
        const auto t0 = multiply_conjugate_s16_s32(s0, z);
        const auto t1 = multiply_conjugate_s16_s32(s1, s0);
        z = s1;
        const int32_t theta0_int = angle_approx_0deg27(t0) * ks16;
        const int32_t theta0_sat = __SSAT(theta0_int, 16);
        const int32_t theta1_int = angle_approx_0deg27(t1) * ks16;
        const int32_t theta1_sat = __SSAT(theta1_int, 16);
        *__SIMD32(dst_p)++ = __PKHBT(
            theta0_sat,
            theta1_sat,
            16);
    }
    z_ = z;

    return {dst.p, src.count, src.sampling_rate};
}

void FM::configure(const float sampling_rate, const float deviation_hz) {
    /*
     * angle: -pi to pi. output range: -32768 to 32767.
     * Maximum delta-theta (output of atan2) at maximum deviation frequency:
     * delta_theta_max = 2 * pi * deviation / sampling_rate
     */
    kf = static_cast<float>(1.0f / (2.0 * pi * deviation_hz / sampling_rate));
    ks16 = 32767.0f * kf;
}

}  // namespace demodulate
}  // namespace dsp