cs_RssiAndChannel.h

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/*
 * Author: Crownstone Team
 * Copyright: Crownstone (https://crownstone.rocks)
 * Date: Sep 15, 2021
 * License: LGPLv3+, Apache License 2.0, and/or MIT (triple-licensed)
 */
 
#pragma once
 
#include <util/cs_Math.h>
 
// ---------------------------------------------------------------------
 
uint8_t inline compressChannel(uint8_t channel) {
    switch (channel) {
        case 37: return 1;
        case 38: return 2;
        case 39: return 3;
        default: return 0;
    }
}
 
uint8_t inline decompressChannel(uint8_t compressedChannel) {
    return compressedChannel == 0 ? 0 : compressedChannel + 36;
}
 
uint8_t inline compressRssi(int8_t rssi) {
    if (rssi < 0) {
        rssi = -rssi;
    }
    else {
        // All positive values are compressed to 0.
        rssi = 0;
    }
 
    return rssi / 2;
}
 
int8_t inline decompressRssi(uint8_t compressedRssi) {
    return -2 * compressedRssi;
}
 
// ---------------------------------------------------------------------
 
class rssi_and_channel_float_t {
public:
    float _rssi;       // signed rssi, usually negative. higher is closer.
    uint8_t _channel;  // 37-39
 
    rssi_and_channel_float_t(float rssi, uint8_t channel = 0) : _rssi(rssi), _channel(channel) {}
 
    bool isCloserThan(const rssi_and_channel_float_t& other) { return _rssi > other._rssi; }
 
    bool isCloserEqual(const rssi_and_channel_float_t& other) { return isCloserThan(other) || _rssi == other._rssi; }
 
    rssi_and_channel_float_t fallOff(float rate_db_sec, float dt_sec) {
        return rssi_and_channel_float_t(_rssi - rate_db_sec * dt_sec, _channel);
    }
};
 
// ---------------------------------------------------------------------
 
struct __attribute__((__packed__)) rssi_and_channel_t {
    uint8_t channel : 2;     // 0 = unknown, 1 = channel 37, 2 = channel 38, 3 = channel 39
    uint8_t rssiHalved : 6;  // half of the absolute value of the original rssi.
 
    rssi_and_channel_t() = default;
 
    rssi_and_channel_t(int8_t rssi, uint8_t ch = 0) {
        channel    = compressChannel(ch);
        rssiHalved = compressRssi(rssi);
    }
 
    uint8_t getChannel() const { return decompressChannel(channel); }
 
    int8_t getRssi() const { return decompressRssi(rssiHalved); }
 
    rssi_and_channel_float_t toFloat() { return rssi_and_channel_float_t(getRssi(), getChannel()); }
 
    rssi_and_channel_float_t fallOff(float rate_db_sec, float dt_sec) { return toFloat().fallOff(rate_db_sec, dt_sec); }
};