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/*
* Copyright (C) 2023 Kyle Reed, zxkmm
*
* 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.
*/
/* Helpers for handling oversampling and interpolation. */
#ifndef __OVERSAMPLE_H__
#define __OVERSAMPLE_H__
#include "message.hpp"
#include "utility.hpp"
/* TODO:
* The decision to oversample/interpolate should only be a baseband concern.
* However, the baseband can't set up the radio (M0 code), so the apps also
* need to know about the "actual" sample rate so the radio settings can be
* applied correctly. Ideally the baseband would tell the apps what the
* actual sample rate is. Currently the apps are telling the baseband and
* that feels like a separation of concerns problem. */
/* HackRF suggests a minimum sample rate of 2M so a oversample rate is applied
* to the sample rate (pre-scale) to get the sample rate closer to that target.
* The baseband needs to know how to correctly decimate (or interpolate) so
* the set of allowed scalars is fixed (See OversampleRate enum).
* In testing, a minimum rate of 400kHz seems to the functional minimum.
*/
/* Gets the oversample rate for a given sample rate.
* The oversample rate is used to increase the sample rate to improve SNR and quality.
* This is also used as the interpolation rate when replaying captures. */
inline OversampleRate get_oversample_rate(uint32_t sample_rate) {
if (sample_rate < 50'000) return OversampleRate::x128; // 25kk..12k5, prepared for future, OVS ok, but decim. :128 still not implemented.
if (sample_rate < 100'000) return OversampleRate::x64; // 50k, prepared for future, OVS ok, but decim. :64 still not implemented.
if (sample_rate < 250'000) return OversampleRate::x16; // Now tentatively applied to 150k..100k - but as soon as we got decim :32, (150k x16, and 100k x32)
return OversampleRate::x8; // 250k .. 1Mhz, that decim :8 , is already applied.(OVS and decim OK)
}
/* Gets the actual sample rate for a given sample rate.
* This is the rate with the correct oversampling rate applied. */
inline uint32_t get_actual_sample_rate(uint32_t sample_rate) {
return sample_rate * toUType(get_oversample_rate(sample_rate));
}
#endif /*__OVERSAMPLE_H__*/