Fixed FT8 v2.0 encoding
This commit is contained in:
Karlis Goba
parent
41e7aef8b8
commit
c2f10e8cb2
6 changed files with 95 additions and 49 deletions
2
Makefile
2
Makefile
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@ -1,5 +1,5 @@
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CXXFLAGS = -std=c++14
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LDFLAGS = -lm
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gen_ft8: gen_ft8.o encode.o pack.o text.o
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gen_ft8: gen_ft8.o encode.o pack.o text.o pack_77.o encode_91.o
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$(CXX) $(LDFLAGS) -o $@ $^
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@ -228,8 +228,8 @@ void genft8(const uint8_t *payload, uint8_t i3, uint8_t *itone) {
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// Append 3 bits of i3 at the end of 72 bit payload
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a87[9] = ((i3 & 0x07) << 5);
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// Calculate CRC of 76 bits (yes, 72 + 3 + 1 zero bit), see WSJT-X code
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uint16_t checksum = ft8_crc(a87, 76);
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// Calculate CRC of 11 bytes = 88 bits, see WSJT-X code
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uint16_t checksum = ft8_crc(a87, 88 - 12);
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// Store the CRC at the end of 75 bit message (yes, 72 + 3)
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uint16_t tmp = (checksum << 1);
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103
encode_91.cpp
103
encode_91.cpp
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@ -1,5 +1,7 @@
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#include "encode.h"
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#include <stdio.h>
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namespace ft8_v2 {
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constexpr int N = 174, K = 91, M = N-K; // Define the LDPC sizes
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@ -109,8 +111,10 @@ const uint8_t colorder[N] = {
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};
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// Costas 7x7 tone pattern
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const uint8_t ICOS7[] = { 2,5,6,0,4,1,3 };
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const uint8_t ICOS7[] = { 3,1,4,0,6,5,2 };
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// Gray code map
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const uint8_t GRAY[8] = { 0,1,3,2,5,6,4,7 };
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// Returns 1 if an odd number of bits are set in x, zero otherwise
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uint8_t parity8(uint8_t x) {
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@ -121,26 +125,26 @@ uint8_t parity8(uint8_t x) {
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}
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// Encode an 87-bit message and return a 174-bit codeword.
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// Encode a 91-bit message and return a 174-bit codeword.
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// The generator matrix has dimensions (87,87).
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// The code is a (174,87) regular ldpc code with column weight 3.
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// The code is a (174,91) regular ldpc code with column weight 3.
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// The code was generated using the PEG algorithm.
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// After creating the codeword, the columns are re-ordered according to
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// "colorder" to make the codeword compatible with the parity-check matrix
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// Arguments:
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// [IN] message - array of 87 bits stored as 11 bytes (MSB first)
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// [IN] message - array of 91 bits stored as 12 bytes (MSB first)
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// [OUT] codeword - array of 174 bits stored as 22 bytes (MSB first)
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void encode174(const uint8_t *message, uint8_t *codeword) {
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// Here we don't generate the generator bit matrix as in WSJT-X implementation
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// Instead we access the generator bits straight from the binary representation in G
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// Also we don't use the itmp temporary buffer, instead filling codeword bit by bit
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// in the reordered order as we compute the result.
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// For reference:
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// itmp(1:M)=pchecks
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// itmp(M+1:N)=message(1:K)
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// codeword(colorder+1)=itmp(1:N)
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// codeword(1:K)=message
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// codeword(K+1:N)=pchecks
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printf("Encode ");
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for (int i = 0; i < K_BYTES; ++i) {
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printf("%02x ", message[i]);
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}
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printf("\n");
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int colidx = 0; // track the current column in codeword
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@ -149,6 +153,22 @@ void encode174(const uint8_t *message, uint8_t *codeword) {
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codeword[i] = 0;
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}
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// Compute the second part of itmp (M+1:N) and store the result in codeword
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uint8_t mask = 0x80; // Rolling mask starting with the MSB
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for (int j = 0; j < K; ++j) {
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// Copy the j-th bit from message to codeword
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if (message[j/8] & mask) {
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//uint8_t col = colorder[colidx]; // Index of the bit to set
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uint8_t col = colidx;
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codeword[col/8] |= (1 << (7 - col%8));
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}
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++colidx;
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// Roll the bitmask to the right
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mask >>= 1;
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if (mask == 0) mask = 0x80;
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}
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// Compute the first part of itmp (1:M) and store the result in codeword
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for (int i = 0; i < M; ++i) { // do i=1,M
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// Fast implementation of bitwise multiplication and parity checking
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@ -161,26 +181,18 @@ void encode174(const uint8_t *message, uint8_t *codeword) {
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}
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// Check if we need to set a bit in codeword
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if (nsum % 2) { // pchecks(i)=mod(nsum,2)
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uint8_t col = colorder[colidx]; // Index of the bit to set
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//uint8_t col = colorder[colidx]; // Index of the bit to set
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uint8_t col = colidx;
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codeword[col/8] |= (1 << (7 - col%8));
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}
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++colidx;
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}
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// Compute the second part of itmp (M+1:N) and store the result in codeword
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uint8_t mask = 0x80; // Rolling mask starting with the MSB
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for (int j = 0; j < K; ++j) {
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// Copy the j-th bit from message to codeword
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if (message[j/8] & mask) {
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uint8_t col = colorder[colidx]; // Index of the bit to set
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codeword[col/8] |= (1 << (7 - col%8));
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}
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++colidx;
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// Roll the bitmask to the right
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mask >>= 1;
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if (mask == 0) mask = 0x80;
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printf("Result ");
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for (int i = 0; i < (N + 7) / 8; ++i) {
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printf("%02x ", codeword[i]);
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}
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printf("\n");
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}
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@ -192,6 +204,12 @@ uint16_t ft8_crc(uint8_t *message, int num_bits) {
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constexpr int WIDTH = 14;
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constexpr uint16_t TOPBIT = (1 << (WIDTH - 1));
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printf("CRC, %d bits: ", num_bits);
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for (int i = 0; i < (num_bits + 7) / 8; ++i) {
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printf("%02x ", message[i]);
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}
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printf("\n");
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uint16_t remainder = 0;
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int idx_byte = 0;
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@ -211,6 +229,7 @@ uint16_t ft8_crc(uint8_t *message, int num_bits) {
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remainder = (remainder << 1);
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}
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}
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printf("CRC = %04xh\n", remainder & ((1 << WIDTH) - 1));
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return remainder & ((1 << WIDTH) - 1);
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}
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@ -227,13 +246,18 @@ void genft8(const uint8_t *payload, uint8_t *itone) {
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// Clear 3 bits after the payload to make 80 bits
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a91[9] &= 0xF8;
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a91[10] = 0;
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a91[11] = 0;
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// Calculate CRC of 80 bits (yes, 77 + 3 zero bits), see WSJT-X code
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uint16_t checksum = ft8_crc(a91, 80);
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// Calculate CRC of 12 bytes = 96 bits, see WSJT-X code
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uint16_t checksum = ft8_crc(a91, 96 - 14);
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// 3dcf = 0011 1101 1100 1111
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// 111 1011 1001 111
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// Store the CRC at the end of 77 bit message
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a91[9] |= (uint8_t)(checksum >> 11);
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a91[10] = (uint8_t)(checksum >> 3);
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a91[11] = (uint8_t)(checksum << 5);
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// a87 contains 77 bits of payload + 14 bits of CRC
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uint8_t codeword[22];
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@ -247,18 +271,27 @@ void genft8(const uint8_t *payload, uint8_t *itone) {
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}
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int k = 7; // Skip over the first set of Costas symbols
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uint8_t mask = 0x80;
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int i_byte = 0;
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for (int j = 0; j < ND; ++j) { // do j=1,ND
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if (j == 29) {
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k += 7; // Skip over the second set of Costas symbols
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}
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// Extract 3 bits from codeword at i-th position
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itone[k] = 0;
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int i = 3*j;
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if (codeword[i/8] & (1 << (7 - i%8))) itone[k] |= 4;
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++i;
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if (codeword[i/8] & (1 << (7 - i%8))) itone[k] |= 2;
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++i;
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if (codeword[i/8] & (1 << (7 - i%8))) itone[k] |= 1;
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uint8_t bits3 = 0;
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if (codeword[i_byte] & mask) bits3 |= 4;
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if (0 == (mask >>= 1)) { mask = 0x80; i_byte++; }
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if (codeword[i_byte] & mask) bits3 |= 2;
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if (0 == (mask >>= 1)) { mask = 0x80; i_byte++; }
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if (codeword[i_byte] & mask) bits3 |= 1;
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if (0 == (mask >>= 1)) { mask = 0x80; i_byte++; }
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// Before Gray: 2560413 00000000117314000020544743734 2560413 74502537003717523102453566214 2560413
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// After Gray: 2560413 00000000117215000030655752725 2560413 75603627002717632103562644315 2560413
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itone[k] = GRAY[bits3];
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++k;
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}
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}
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13
gen_ft8.cpp
13
gen_ft8.cpp
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@ -6,6 +6,9 @@
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#include "pack.h"
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#include "encode.h"
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#include "pack_77.h"
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#include "encode_91.h"
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void convert_8bit_to_6bit(uint8_t *dst, const uint8_t *src, int nBits) {
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// Zero-fill the destination array as we will only be setting bits later
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@ -169,8 +172,9 @@ int main(int argc, char **argv) {
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const char *wav_path = argv[2];
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// First, pack the text data into 72-bit binary message
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uint8_t packed[9];
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int rc = packmsg(message, packed);
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uint8_t packed[10];
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//int rc = packmsg(message, packed);
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int rc = ft8_v2::pack77(message, packed);
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if (rc < 0) {
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printf("Cannot parse message!\n");
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printf("RC = %d\n", rc);
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@ -178,14 +182,15 @@ int main(int argc, char **argv) {
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}
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printf("Packed data: ");
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for (int j = 0; j < 9; ++j) {
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for (int j = 0; j < 10; ++j) {
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printf("%02x ", packed[j]);
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}
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printf("\n");
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// Second, encode the binary message as a sequence of FSK tones
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uint8_t tones[NN]; // NN = 79, lack of better name at the moment
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genft8(packed, 0, tones);
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//genft8(packed, 0, tones);
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ft8_v2::genft8(packed, tones);
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printf("FSK tones: ");
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for (int j = 0; j < NN; ++j) {
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20
pack_77.cpp
20
pack_77.cpp
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@ -3,6 +3,8 @@
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#include "text.h"
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#include <stdio.h>
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namespace ft8_v2 {
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// TODO: This is wasteful, should figure out something more elegant
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@ -77,6 +79,7 @@ int32_t pack28(const char *callsign) {
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(i2 = index(A3, c6[2])) >= 0 && (i3 = index(A4, c6[3])) >= 0 &&
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(i4 = index(A4, c6[4])) >= 0 && (i5 = index(A4, c6[5])) >= 0)
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{
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printf("Pack28: idx=[%d, %d, %d, %d, %d, %d]\n", i0, i1, i2, i3, i4, i5);
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// This is a standard callsign
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int32_t n28 = i0;
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n28 = n28 * 36 + i1;
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@ -84,6 +87,7 @@ int32_t pack28(const char *callsign) {
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n28 = n28 * 27 + i3;
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n28 = n28 * 27 + i4;
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n28 = n28 * 27 + i5;
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printf("Pack28: n28=%d (%04xh)\n", n28, n28);
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return NTOKENS + MAX22 + n28;
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}
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@ -144,10 +148,10 @@ uint16_t packgrid(const char *grid4) {
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is_digit(grid4[2]) && is_digit(grid4[3]))
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{
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//if (w(3).eq.'R ') ir=1
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uint16_t igrid4 = (grid4[3] - '0');
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uint16_t igrid4 = (grid4[0] - 'A');
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igrid4 = igrid4 * 18 + (grid4[1] - 'A');
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igrid4 = igrid4 * 10 + (grid4[2] - '0');
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igrid4 = igrid4 * 10 + (grid4[1] - 'A');
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igrid4 = igrid4 * 18 + (grid4[0] - 'A');
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igrid4 = igrid4 * 10 + (grid4[3] - '0');
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return igrid4;
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}
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@ -208,14 +212,18 @@ int pack77_1(const char *msg, uint8_t *b77) {
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// write(c77,1000) n28a,ipa,n28b,ipb,ir,igrid4,i3
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// 1000 format(2(b28.28,b1),b1,b15.15,b3.3)
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// 00 00 00 27 b3 00 01 0b 27 8f b9 e0
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// (00 00 00 2) 0 (f0 85 ab e) (0)
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// 7842D5F
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b77[0] = (n28a >> 21);
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b77[1] = (n28a >> 13);
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b77[2] = (n28a >> 5);
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b77[3] = (uint8_t)(n28a << 3) | (uint8_t)(n28b >> 26);
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b77[4] = (n28b >> 18);
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b77[5] = (n28a >> 10);
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b77[6] = (n28a >> 2);
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b77[7] = (uint8_t)(n28a << 6) | (uint8_t)(igrid4 >> 10);
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b77[5] = (n28b >> 10);
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b77[6] = (n28b >> 2);
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b77[7] = (uint8_t)(n28b << 6) | (uint8_t)(igrid4 >> 10);
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b77[8] = (igrid4 >> 2);
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b77[9] = (uint8_t)(igrid4 << 6) | (uint8_t)(i3 << 3);
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@ -7,6 +7,6 @@ namespace ft8_v2 {
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// Pack FT8 text message into 72 bits
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// [IN] msg - FT8 message (e.g. "CQ TE5T KN01")
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// [OUT] c77 - 10 byte array to store the 77 bit payload (MSB first)
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int pack77(const char *msg, uint8_t *c77)
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int pack77(const char *msg, uint8_t *c77);
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};
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