alanbjohnston
5 years ago
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@ -0,0 +1,152 @@
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/*
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* TelemEncoding.c
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*
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Fox-1 telemetry encoder
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January 2014 Phil Karn KA9Q
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This file has two external functions:
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void update_rs(unsigned char parity[32],unsigned char data);
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int encode_8b10b(int *state,int data).
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update_rs() is the Reed-Solomon encoder. Its first argument is the 32-byte
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encoder shift register, the second is the 8-bit data byte being encoded. It updates
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the shift register in place and returns void. At the end of each frame, it contains
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the parities ready for transmission, starting with parity[0].
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Be sure to zero this array before each new frame!
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encode_8b10b() is the 8b10b encoder. Its first argument is a pointer to a single integer
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with the 1-bit encoder state (the current run disparity, or RD). Initialize it to 0
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JUST ONCE at startup (not between frames).
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The second argument is the data byte being encoded. It updates the state and returns
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an integer containing the 10-bit encoded word, right justified.
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Transmit this word from left to right.
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The data argument is an int so it can hold the special value -1 to indicate end of frame;
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it generates the 8b10b control word K.28.5, which is used as an inter-frame flag.
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Some assert() calls are made to verify legality of arguments. These can be turned off in
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production code.
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sample frame transmission code:
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unsigned char data[64]; // Data block to be sent
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unsigned char parity[32]; // RS parities
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void transmit_word(int); // User provided transmit function: 10 bits of data in bits 9....0
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int state,i;
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state = 0; // Only once at startup, not between frames
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memset(parity,0,sizeof(parity); // Do this before every frame
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// Transmit the data, updating the RS encoder
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for(i=0;i<64;i++){
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update_rs(parity,data[i]);
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transmit_word(encode_8b10b(&state,data[i]);
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}
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// get the RS parities
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for(i=0;i<32;i++)
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transmit_word(encode_8b10b(&state,parity[i]);
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transmit_word(encode_8b10b(&state,-1); // Transmit end-of-frame flag
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*/
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#include <string.h>
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//#include "Fox.h"
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#include "TelemEncoding.h"
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#ifndef NULL
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#define NULL ((void *)0)
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#endif
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#define NN (0xff) // Frame size in symbols
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#define A0 (NN) // special value for log(0)
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// GF Antilog lookup table table
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static unsigned char CCSDS_alpha_to[NN+1] = {
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0x01,0x02,0x04,0x08,0x10,0x20,0x40,0x80,0x87,0x89,0x95,0xad,0xdd,0x3d,0x7a,0xf4,
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0x6f,0xde,0x3b,0x76,0xec,0x5f,0xbe,0xfb,0x71,0xe2,0x43,0x86,0x8b,0x91,0xa5,0xcd,
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0x1d,0x3a,0x74,0xe8,0x57,0xae,0xdb,0x31,0x62,0xc4,0x0f,0x1e,0x3c,0x78,0xf0,0x67,
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0xce,0x1b,0x36,0x6c,0xd8,0x37,0x6e,0xdc,0x3f,0x7e,0xfc,0x7f,0xfe,0x7b,0xf6,0x6b,
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0xd6,0x2b,0x56,0xac,0xdf,0x39,0x72,0xe4,0x4f,0x9e,0xbb,0xf1,0x65,0xca,0x13,0x26,
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0x4c,0x98,0xb7,0xe9,0x55,0xaa,0xd3,0x21,0x42,0x84,0x8f,0x99,0xb5,0xed,0x5d,0xba,
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0xf3,0x61,0xc2,0x03,0x06,0x0c,0x18,0x30,0x60,0xc0,0x07,0x0e,0x1c,0x38,0x70,0xe0,
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0x47,0x8e,0x9b,0xb1,0xe5,0x4d,0x9a,0xb3,0xe1,0x45,0x8a,0x93,0xa1,0xc5,0x0d,0x1a,
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0x34,0x68,0xd0,0x27,0x4e,0x9c,0xbf,0xf9,0x75,0xea,0x53,0xa6,0xcb,0x11,0x22,0x44,
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0x88,0x97,0xa9,0xd5,0x2d,0x5a,0xb4,0xef,0x59,0xb2,0xe3,0x41,0x82,0x83,0x81,0x85,
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0x8d,0x9d,0xbd,0xfd,0x7d,0xfa,0x73,0xe6,0x4b,0x96,0xab,0xd1,0x25,0x4a,0x94,0xaf,
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0xd9,0x35,0x6a,0xd4,0x2f,0x5e,0xbc,0xff,0x79,0xf2,0x63,0xc6,0x0b,0x16,0x2c,0x58,
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0xb0,0xe7,0x49,0x92,0xa3,0xc1,0x05,0x0a,0x14,0x28,0x50,0xa0,0xc7,0x09,0x12,0x24,
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0x48,0x90,0xa7,0xc9,0x15,0x2a,0x54,0xa8,0xd7,0x29,0x52,0xa4,0xcf,0x19,0x32,0x64,
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0xc8,0x17,0x2e,0x5c,0xb8,0xf7,0x69,0xd2,0x23,0x46,0x8c,0x9f,0xb9,0xf5,0x6d,0xda,
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0x33,0x66,0xcc,0x1f,0x3e,0x7c,0xf8,0x77,0xee,0x5b,0xb6,0xeb,0x51,0xa2,0xc3,0x00,
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};
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// GF log lookup table. Special value represents log(0)
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static unsigned char CCSDS_index_of[NN+1] = {
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A0, 0, 1, 99, 2,198,100,106, 3,205,199,188,101,126,107, 42,
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4,141,206, 78,200,212,189,225,102,221,127, 49,108, 32, 43,243,
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5, 87,142,232,207,172, 79,131,201,217,213, 65,190,148,226,180,
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103, 39,222,240,128,177, 50, 53,109, 69, 33, 18, 44, 13,244, 56,
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6,155, 88, 26,143,121,233,112,208,194,173,168, 80,117,132, 72,
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202,252,218,138,214, 84, 66, 36,191,152,149,249,227, 94,181, 21,
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104, 97, 40,186,223, 76,241, 47,129,230,178, 63, 51,238, 54, 16,
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110, 24, 70,166, 34,136, 19,247, 45,184, 14, 61,245,164, 57, 59,
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7,158,156,157, 89,159, 27, 8,144, 9,122, 28,234,160,113, 90,
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209, 29,195,123,174, 10,169,145, 81, 91,118,114,133,161, 73,235,
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203,124,253,196,219, 30,139,210,215,146, 85,170, 67, 11, 37,175,
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192,115,153,119,150, 92,250, 82,228,236, 95, 74,182,162, 22,134,
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105,197, 98,254, 41,125,187,204,224,211, 77,140,242, 31, 48,220,
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130,171,231, 86,179,147, 64,216, 52,176,239, 38, 55, 12, 17, 68,
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111,120, 25,154, 71,116,167,193, 35, 83,137,251, 20, 93,248,151,
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46, 75,185, 96, 15,237, 62,229,246,135,165, 23, 58,163, 60,183,
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};
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// Only half the coefficients are given here because the
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// generator polynomial is palindromic; G0 = G32, G1 = G31, etc.
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// Only G16 is unique
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static unsigned char CCSDS_poly[] = {
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0,249, 59, 66, 4, 43,126,251, 97, 30, 3,213, 50, 66,170, 5,
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24,
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};
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static inline int modnn(int x){
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while (x >= NN) {
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x -= NN;
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x = (x >> 8) + (x & NN);
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}
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return x;
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}
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// Update Reed-Solomon encoder
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// parity -> 32-byte reed-solomon encoder state; clear this to zero before each frame
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void update_rs(
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unsigned char parity[32], // 32-byte encoder state; zero before each frame
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unsigned char c) // Current data byte to update
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{
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unsigned char feedback;
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int j,t;
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assert(parity != NULL);
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feedback = CCSDS_index_of[c ^ parity[0]];
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if(feedback != A0){ // only if feedback is non-zero
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// Take advantage of palindromic polynomial to halve the multiplies
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// Do G1...G15, which is the same as G17...G31
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for(j=1;j<NP/2;j++){
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t = CCSDS_alpha_to[modnn(feedback + CCSDS_poly[j])];
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parity[j] ^= t;
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parity[NP-j] ^= t;
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}
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// Do G16, which is used in only parity[16]
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t = CCSDS_alpha_to[modnn(feedback + CCSDS_poly[j])];
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parity[j] ^= t;
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}
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// shift left
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memmove(&parity[0],&parity[1],NP-1);
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// G0 is 1 in alpha form, 0 in index form; don't need to multiply by it
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parity[NP-1] = CCSDS_alpha_to[feedback];
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//taskYIELD();
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}
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#define SYNC (0x0fa) // K.28.5, RD=-1
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void write_little_endian(unsigned int word, int num_bytes, FILE *wav_file)
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{
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unsigned buf;
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while(num_bytes>0)
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{ buf = word & 0xff;
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fwrite(&buf, 1,1, wav_file);
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num_bytes--;
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word >>= 8;
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}
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}
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