portapack-mayhem/firmware/common/oversample.hpp
Brumi-2021 a4636d7872
Finalise all low bit rate Capture App with x64 (#1386)
* Finalise all low bit rate Capture App with x64

* Adding back also 25k BW option
2023-08-18 14:49:22 +02:00

74 lines
3.4 KiB
C++

/*
* 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.
*
* There are several different concepts or terms related to Capture and Replay,
* (1) oversampling (x8, x16 ,...) / decimation (/8, /16...)
* In Capture App , when ADC can not handle directly a requiered low sample rates ,
* we need to apply oversampling (x8. x16 ex) , getting more real samples than needed) by "x_number" ,
* and later to write it to SD card with the proper needed real sample rate , we apply Decimation , "/ number" .
*
* (2) up-sampling or re-escale or interpolation. (x8, x16, ...)
* In Replay-list App, when we got too low bit rate data for Hackrf ,
* we need to upsampling or interpolate or resampling to increase those low bit rates
* to a proper sample rate higher than the min. to be able to be transmitted by Hackrf.
*/
/* 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 < 30'000) return OversampleRate::x64; // 25k, 16k, 12k5.
if (sample_rate < 80'000) return OversampleRate::x32; // 75k, 50k, 32k.
if (sample_rate < 250'000) return OversampleRate::x16; // 100k and 150k.
return OversampleRate::x8; // 250k .. 1Mhz, that decim x8 , is already applied.(OVerSampling 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__*/