spektrum_rssi.h
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/****************************************************************************
*
* Copyright (c) 2012-2015 PX4 Development Team. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name PX4 nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************/
/**
* @file spektrum_rssi.h
*
* RSSI dBm to percentage conversion for Spektrum telemetry receivers
*
* @author Kurt Kiefer <kekiefer@gmail.com>
*/
#pragma once
#include <climits>
/*
min_rssi_dbm = -92.0
max_rssi_dbm = -42.0
def dbm_to_percent(abs_dbm):
if -abs_dbm < min_rssi_dbm:
return 0.0
elif -abs_dbm > max_rssi_dbm:
return 100.0
else:
return 100.0 * math.log10(1.0 + (float)(-abs_dbm - min_rssi_dbm) * (9.0 / (max_rssi_dbm - min_rssi_dbm)))
*/
constexpr int8_t lu_dbm_percent[] = {
100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100,
100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100,
100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 99, 98, 98, 97, 96,
95, 94, 93, 92, 91, 90, 89, 88, 87, 86, 85, 84, 83, 82, 81, 79,
78, 77, 75, 74, 73, 71, 70, 68, 66, 65, 63, 61, 59, 57, 55, 52,
50, 47, 45, 42, 39, 35, 32, 28, 24, 19, 13, 7, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0,
};
#define MASK(n) (n >> (sizeof(n) * CHAR_BIT - 1))
/* constexpr-compatible version of abs() */
constexpr unsigned c_abs(int n)
{
return (n + MASK(n)) ^ MASK(n);
}
/* convert signed spektrum dbm (-92 to -42) to percentage */
constexpr int8_t spek_dbm_to_percent(int8_t dbm)
{
return lu_dbm_percent[c_abs(dbm)];
}
static_assert(spek_dbm_to_percent(0) == 100, "0 dbm should be 100%");
static_assert(spek_dbm_to_percent(-42) == 100, "-42 dbm should be 100%");
static_assert(spek_dbm_to_percent(-80) == 50, "-80 dbm should be 50%");
static_assert(spek_dbm_to_percent(-92) == 0, "-92 dbm should be 0%");
static_assert(spek_dbm_to_percent(-128) == 0, "-128 dbm should be 0%");