mayhem-firmware/firmware/baseband/channel_decimator.cpp

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/*
* 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 "channel_decimator.hpp"
buffer_c16_t ChannelDecimator::execute_decimation(const buffer_c8_t& buffer) {
const buffer_c16_t work_baseband_buffer {
work_baseband.data(),
work_baseband.size()
};
const buffer_s16_t work_audio_buffer {
(int16_t*)work_baseband.data(),
sizeof(work_baseband) / sizeof(int16_t)
};
/* 3.072MHz complex<int8_t>[2048], [-128, 127]
* -> Shift by -fs/4
* -> 3rd order CIC: -0.1dB @ 0.028fs, -1dB @ 0.088fs, -60dB @ 0.468fs
* -0.1dB @ 86kHz, -1dB @ 270kHz, -60dB @ 1.44MHz
* -> gain of 256
* -> decimation by 2
* -> 1.544MHz complex<int16_t>[1024], [-32768, 32512] */
auto stage_0_out = execute_stage_0(buffer, work_baseband_buffer);
if( decimation_factor == DecimationFactor::By2 ) {
return stage_0_out;
}
/* 1.536MHz complex<int16_t>[1024], [-32768, 32512]
* -> 3rd order CIC: -0.1dB @ 0.028fs, -1dB @ 0.088fs, -60dB @ 0.468fs
* -0.1dB @ 43kHz, -1dB @ 136kHz, -60dB @ 723kHz
* -> gain of 8
* -> decimation by 2
* -> 768kHz complex<int16_t>[512], [-8192, 8128] */
auto cic_1_out = cic_1.execute(stage_0_out, work_baseband_buffer);
if( decimation_factor == DecimationFactor::By4 ) {
return cic_1_out;
}
/* 768kHz complex<int16_t>[512], [-32768, 32512]
* -> 3rd order CIC decimation by 2, gain of 1
* -> 384kHz complex<int16_t>[256], [-32768, 32512] */
auto cic_2_out = cic_2.execute(cic_1_out, work_baseband_buffer);
if( decimation_factor == DecimationFactor::By8 ) {
return cic_2_out;
}
/* 384kHz complex<int16_t>[256], [-32768, 32512]
* -> 3rd order CIC decimation by 2, gain of 1
* -> 192kHz complex<int16_t>[128], [-32768, 32512] */
auto cic_3_out = cic_3.execute(cic_2_out, work_baseband_buffer);
if( decimation_factor == DecimationFactor::By16 ) {
return cic_3_out;
}
/* 192kHz complex<int16_t>[128], [-32768, 32512]
* -> 3rd order CIC decimation by 2, gain of 1
* -> 96kHz complex<int16_t>[64], [-32768, 32512] */
auto cic_4_out = cic_4.execute(cic_3_out, work_baseband_buffer);
return cic_4_out;
}
buffer_c16_t ChannelDecimator::execute_stage_0(
const buffer_c8_t& buffer,
const buffer_c16_t& work_baseband_buffer
) {
if( fs_over_4_downconvert ) {
return translate.execute(buffer, work_baseband_buffer);
} else {
return cic_0.execute(buffer, work_baseband_buffer);
}
}