mirror of
https://github.com/portapack-mayhem/mayhem-firmware.git
synced 2024-12-15 20:50:28 +00:00
12dbf957b3
* working_x32_Capture_till_75Khz * format issues * apply better accurate comments * auto format issues
75 lines
3.6 KiB
C++
75 lines
3.6 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 < 50'000) return OversampleRate::x128; // 25k..12k5, prepared for future, OVS ok, but decim. x128 still not implemented.
|
|
if (sample_rate < 100'000) return OversampleRate::x64; // 50k, prepared for future, OVS ok, but decim. x64 still not implemented.
|
|
if (sample_rate < 150'000) return OversampleRate::x32; // 100k needs x32
|
|
if (sample_rate < 250'000) return OversampleRate::x16; // 150k needs x16
|
|
|
|
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__*/
|