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sdrangel/modemm17/LinkSetupFrame.h
2022-07-31 05:15:58 +02:00

183 lines
5.2 KiB
C++

// Copyright 2020 Mobilinkd LLC.
#pragma once
#include <array>
#include <cstdint>
#include <cmath>
#include <stdexcept>
#include <algorithm>
#include "export.h"
namespace modemm17
{
struct MODEMM17_API LinkSetupFrame
{
using call_t = std::array<char,10>; // NUL-terminated C-string.
using encoded_call_t = std::array<uint8_t, 6>;
using gnss_t = std::array<uint8_t, 14>;
using frame_t = std::array<uint8_t, 30>;
static const encoded_call_t BROADCAST_ADDRESS;
static const call_t BROADCAST_CALL;
enum TxType { PACKET, STREAM };
enum DataType { DT_RESERVED, DATA, VOICE, MIXED };
enum EncType { NONE, AES, LFSR, ET_RESERVED };
call_t tocall_ = {0}; // Destination
call_t mycall_ = {0}; // Source
TxType tx_type_ = TxType::STREAM;
DataType data_type_ = DataType::VOICE;
EncType encryption_type_ = EncType::NONE;
/**
* The callsign is encoded in base-40 starting with the right-most
* character. The final value is written out in "big-endian" form, with
* the most-significant value first. This leads to 0-padding of shorter
* callsigns.
*
* @param[in] callsign is the callsign to encode.
* @param[in] strict is a flag (disabled by default) which indicates whether
* invalid characters are allowed and assugned a value of 0 or not allowed,
* resulting in an exception.
* @return the encoded callsign as an array of 6 bytes.
* @throw invalid_argument when strict is true and an invalid callsign (one
* containing an unmappable character) is passed.
*/
static encoded_call_t encode_callsign(call_t callsign, bool strict = false)
{
// Encode the characters to base-40 digits.
uint64_t encoded = 0;
std::reverse(callsign.begin(), callsign.end());
for (auto c : callsign)
{
encoded *= 40;
if ((c >= 'A') && (c <= 'Z'))
{
encoded += c - 'A' + 1;
}
else if ((c >= '0') && (c <= '9'))
{
encoded += c - '0' + 27;
}
else if (c == '-')
{
encoded += 37;
}
else if (c == '/')
{
encoded += 38;
}
else if (c == '.')
{
encoded += 39;
}
else if (strict)
{
throw std::invalid_argument("bad callsign");
}
}
const auto p = reinterpret_cast<uint8_t*>(&encoded);
encoded_call_t result;
std::copy(p, p + 6, result.rbegin());
return result;
}
/**
* Decode a base-40 encoded callsign to its text representation. This decodes
* a 6-byte big-endian value into a string of up to 9 characters.
*/
static call_t decode_callsign(encoded_call_t callsign)
{
static const char callsign_map[] = "xABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-/.";
call_t result;
if (callsign == BROADCAST_ADDRESS)
{
result = BROADCAST_CALL;
return result;
}
uint64_t encoded = 0; // This only works on little endian architectures.
auto p = reinterpret_cast<uint8_t*>(&encoded);
std::copy(callsign.rbegin(), callsign.rend(), p);
// decode each base-40 digit and map them to the appriate character.
result.fill(0);
size_t index = 0;
while (encoded)
{
result[index++] = callsign_map[encoded % 40];
encoded /= 40;
}
return result;
}
static gnss_t encode_gnss(float lat, float lon, float alt)
{
gnss_t result;
result.fill(0);
double lat_int, lat_frac;
double lon_int, lon_frac;
uint16_t lat_dec, lon_dec;
lat_frac = modf(lat, &lat_int);
lon_frac = modf(lon, &lon_int);
bool north = lat_int >= 0;
bool east = lon_int >= 0;
result[2] = (int) std::abs(lat_int);
lat_dec = std::abs(lat_frac) * 65536.0f;
result[3] = lat_dec >> 8;
result[4] = lat_dec & 0xFF;
result[5] = (int) std::abs(lon_int);
lon_dec = std::abs(lon_frac) * 65536.0f;
result[6] = lon_dec >> 8;
result[7] = lon_dec & 0xFF;
result[8] = (north ? 0 : 1) | ((east ? 0 : 1)<<1) | (1<<2);
uint16_t alt_enc = (alt * 3.28084f) + 1500;
result[9] = alt_enc >> 8;
result[10] = alt_enc & 0xFF;
return result;
}
static void decode_gnss(const gnss_t& gnss_enc, float& lat, float& lon, float& alt)
{
bool north = (gnss_enc[8] & 1) != 0;
bool east = (gnss_enc[8] & 2) != 0;
uint32_t lat_int = gnss_enc[2];
uint16_t lat_frac = (gnss_enc[3] << 8) + gnss_enc[4];
uint32_t lon_int = gnss_enc[5];
uint16_t lon_frac = (gnss_enc[6] << 8) + gnss_enc[7];
lat = lat_int + (lat_frac / 65536.0f);
lat = north ? lat : -lat;
lon = lon_int + (lon_frac / 65536.0f);
lat = east ? lon : -lon;
uint16_t alt_enc = (gnss_enc[9] << 8) + gnss_enc[10];
alt = (alt_enc - 1500) / 3.28084f;
}
LinkSetupFrame()
{}
LinkSetupFrame& myCall(const char*)
{
return *this;
}
};
} // modemm17