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dsd-fme/p25p1_hdu.c

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/*
* Copyright (C) 2010 DSD Author
* GPG Key ID: 0x3F1D7FD0 (74EF 430D F7F2 0A48 FCE6 F630 FAA2 635D 3F1D 7FD0)
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
* REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
* AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
* INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
* LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
* OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
* PERFORMANCE OF THIS SOFTWARE.
*/
#include "dsd.h"
#include "p25p1_hdu.h"
#include "p25p1_check_hdu.h"
#include "p25p1_heuristics.h"
int
read_dibit (dsd_opts* opts, dsd_state* state, char* output, int* status_count, int* analog_signal, int* did_read_status)
{
int dibit;
int status;
if (*status_count == 35) {
#ifdef TRACE_DSD
char prev_prefix = state->debug_prefix;
state->debug_prefix = 's';
#endif
// Status bits now
status = getDibit (opts, state);
// TODO: do something useful with the status bits...
if (did_read_status != NULL) {
*did_read_status = 1;
}
*status_count = 1;
#ifdef TRACE_DSD
state->debug_prefix = prev_prefix;
#endif
} else {
if (did_read_status != NULL) {
*did_read_status = 0;
}
(*status_count)++;
}
dibit = get_dibit_and_analog_signal (opts, state, analog_signal);
output[0] = (1 & (dibit >> 1)); // bit 1
output[1] = (1 & dibit); // bit 0
return dibit;
}
void
read_dibit_update_analog_data (dsd_opts* opts, dsd_state* state, char* output, unsigned int count, int* status_count,
AnalogSignal* analog_signal_array, int* analog_signal_index)
{
unsigned int i;
unsigned int debug_left, debug_right;
for (i=0; i<count; i+=2)
{
// We read two bits on each call
int analog_signal;
int did_read_status;
int dibit;
dibit = read_dibit(opts, state, output + i, status_count, &analog_signal, &did_read_status);
if (analog_signal_array != NULL)
{
// Fill up the AnalogSignal struct
analog_signal_array[*analog_signal_index].value = analog_signal;
analog_signal_array[*analog_signal_index].dibit = dibit;
analog_signal_array[*analog_signal_index].sequence_broken = did_read_status;
(*analog_signal_index)++;
}
}
}
void
read_word (dsd_opts* opts, dsd_state* state, char* word, unsigned int length, int* status_count,
AnalogSignal* analog_signal_array, int* analog_signal_index)
{
read_dibit_update_analog_data(opts, state, word, length, status_count, analog_signal_array, analog_signal_index);
}
void
read_golay24_parity (dsd_opts* opts, dsd_state* state, char* parity, int* status_count,
AnalogSignal* analog_signal_array, int* analog_signal_index)
{
read_dibit_update_analog_data(opts, state, parity, 12, status_count, analog_signal_array, analog_signal_index);
}
void
read_hamm_parity (dsd_opts* opts, dsd_state* state, char* parity, int* status_count,
AnalogSignal* analog_signal_array, int* analog_signal_index)
{
// Read 2 dibits = read 4 bits.
read_dibit_update_analog_data(opts, state, parity, 4, status_count, analog_signal_array, analog_signal_index);
}
/**
* Corrects a hex (6 bit) word using the Golay 24 FEC.
*/
static void
correct_hex_word (dsd_state* state, char* hex, char* parity)
{
int fixed_errors;
int irrecoverable_errors;
irrecoverable_errors = check_and_fix_golay_24_6(hex, parity, &fixed_errors);
state->debug_header_errors += fixed_errors;
if (irrecoverable_errors != 0)
{
state->debug_header_critical_errors++;
}
}
/**
* Reads an hex word, its parity bits and attempts to error correct it using the Golay24 algorithm.
*/
static void
read_and_correct_hex_word (dsd_opts* opts, dsd_state* state, char* hex, int* status_count,
AnalogSignal* analog_signal_array, int* analog_signal_index)
{
char parity[12];
// Read the hex word
read_word (opts, state, hex, 6, status_count, analog_signal_array, analog_signal_index);
// Read the parity
read_golay24_parity (opts, state, parity, status_count, analog_signal_array, analog_signal_index);
// Use the Golay24 FEC to correct it. This call modifies the content of hex to fix it, hopefully
correct_hex_word (state, hex, parity);
}
/**
* Uses the information from a corrected sequence of hex words to update the AnalogSignal data.
* The proper Golay 24 parity is calculated from the corrected hex word so we can also fix the Golay parity
* that we read originally from the signal.
* \param corrected_hex_data Pointer to a sequence of hex words that has been error corrected and therefore
* we trust it's correct. Typically this are hex words that has been decoded successfully using a
* Reed-Solomon variant.
* \param hex_count The number of hex words in the sequence.
* \param analog_signal_array A pointer to the AnalogSignal information for the sequence of hex words.
*/
static void
correct_golay_dibits_6(char* corrected_hex_data, int hex_count, AnalogSignal* analog_signal_array)
{
int i, j;
int analog_signal_index;
int dibit;
char parity[12];
analog_signal_index = 0;
for (i=hex_count-1; i>=0; i--)
{
for (j=0; j<6; j+=2) // 3 iterations -> 3 dibits
{
// Given the bits, calculates the dibit
dibit = (corrected_hex_data[i*6+j] << 1) | corrected_hex_data[i*6+j+1];
// Now we know the dibit we should have read from the signal
analog_signal_array[analog_signal_index].corrected_dibit = dibit;
#ifdef HEURISTICS_DEBUG
if (analog_signal_array[analog_signal_index].dibit != dibit)
{
printf("HDU data word corrected from %i to %i, analog value %i\n",
analog_signal_array[analog_signal_index].dibit, dibit, analog_signal_array[analog_signal_index].value);
}
#endif
analog_signal_index++;
}
// Calculate the Golay 24 parity for the corrected hex word
encode_golay_24_6(corrected_hex_data+i*6, parity);
// Now we know the parity we should have read from the signal. Use this information
for (j=0; j<12; j+=2) // 6 iterations -> 6 dibits
{
// Given the bits, calculates the dibit
dibit = (parity[j] << 1) | parity[j+1];
// Now we know the dibit we should have read from the signal
analog_signal_array[analog_signal_index].corrected_dibit = dibit;
#ifdef HEURISTICS_DEBUG
if (analog_signal_array[analog_signal_index].dibit != dibit)
{
printf("HDU parity corrected from %i to %i, analog value %i\n",
analog_signal_array[analog_signal_index].dibit, dibit, analog_signal_array[analog_signal_index].value);
}
#endif
analog_signal_index++;
}
}
}
/**
* The important method that processes a full P25 HD unit.
*/
void
processHDU(dsd_opts* opts, dsd_state* state)
{
char mi[73], mfid[9], algid[9], kid[17], tgid[17], tmpstr[255];
int i, j;
long talkgroup;
int algidhex, kidhex;
char hex[6];
int status_count;
int status;
char hex_data[20][6]; // Data in hex-words (6 bit words). A total of 20 hex words.
char hex_parity[16][6]; // Parity of the data, again in hex-word format. A total of 16 parity hex words.
int irrecoverable_errors;
AnalogSignal analog_signal_array[20*(3+6)+16*(3+6)];
int analog_signal_index;
analog_signal_index = 0;
// we skip the status dibits that occur every 36 symbols
// the next status symbol comes in 14 dibits from here
// so we start counter at 36-14-1 = 21
status_count = 21;
// Read 20 hex words, correct them using their Golay 24 parity data.
for (i=19; i>=0; i--)
{
read_and_correct_hex_word (opts, state, hex, &status_count, analog_signal_array, &analog_signal_index);
// Store the corrected hex word into the hex_data store:
for (j=0; j<6; j++)
{
hex_data[i][j] = hex[j];
}
}
// Read the 16 parity hex word. These are used to FEC the 20 hex words using Reed-Solomon.
for (i=15; i>=0; i--)
{
read_and_correct_hex_word (opts, state, hex, &status_count, analog_signal_array, &analog_signal_index);
// Store the corrected hex word into the hex_parity store:
for (j=0; j<6; j++)
{
hex_parity[i][j] = hex[j];
}
}
// Don't forget to mark the first element as the start of a new sequence
analog_signal_array[0].sequence_broken = 1;
// Use the Reed-Solomon algorithm to correct the data. hex_data is modified in place
irrecoverable_errors = check_and_fix_redsolomon_36_20_17((char*)hex_data, (char*)hex_parity);
if (irrecoverable_errors != 0)
{
// The hex words failed the Reed-Solomon check. There were too many errors. Still we can use this
// information to update an estimate of the BER.
state->debug_header_critical_errors++;
// We can correct (17-1)/2 = 8 errors. If we failed, it means that there were more than 8 errors in
// these 20+16 words. But take into account that each hex word was already error corrected with
// Golay 24, which can correct 3 bits on each sequence of (6+12) bits. We could say that there were
// 9 errors of 4 bits.
update_error_stats(&state->p25_heuristics, 20*6+16*6, 9*4);
}
else
{
// The hex words passed the Reed-Solomon check. This means that very likely they are correct and we
// can trust that the digitizer did a good job with them. In other words, each analog value was
// correctly assigned to a dibit. This is extremely useful information for the digitizer and we are
// going to exploit it.
char fixed_parity[16*6];
// Correct the dibits that we did read according with the newly corrected hex_data values
correct_golay_dibits_6((char*)hex_data, 20, analog_signal_array);
// Generate again the Reed-Solomon parity for the corrected data
encode_reedsolomon_36_20_17((char*)hex_data, fixed_parity);
// Correct the dibits that we read according with the corrected parity values
correct_golay_dibits_6(fixed_parity, 16, analog_signal_array+20*(3+6));
// Now we have a bunch of dibits (composed of data and parity of different kinds) that we trust are all
// correct. We also keep a record of the analog values from where each dibit is coming from.
// This information is gold for the heuristics module.
contribute_to_heuristics(state->rf_mod, &(state->p25_heuristics), analog_signal_array, 20*(3+6)+16*(3+6));
}
// Now put the corrected data on the DSD structures
mi[72] = 0;
mfid[8] = 0;
algid[8] = 0;
kid[16] = 0;
tgid[16] = 0;
mi[ 0] = hex_data[19][0] + '0';
mi[ 1] = hex_data[19][1] + '0';
mi[ 2] = hex_data[19][2] + '0';
mi[ 3] = hex_data[19][3] + '0';
mi[ 4] = hex_data[19][4] + '0';
mi[ 5] = hex_data[19][5] + '0';
mi[ 6] = hex_data[18][0] + '0';
mi[ 7] = hex_data[18][1] + '0';
mi[ 8] = hex_data[18][2] + '0';
mi[ 9] = hex_data[18][3] + '0';
mi[10] = hex_data[18][4] + '0';
mi[11] = hex_data[18][5] + '0';
mi[12] = hex_data[17][0] + '0';
mi[13] = hex_data[17][1] + '0';
mi[14] = hex_data[17][2] + '0';
mi[15] = hex_data[17][3] + '0';
mi[16] = hex_data[17][4] + '0';
mi[17] = hex_data[17][5] + '0';
mi[18] = hex_data[16][0] + '0';
mi[19] = hex_data[16][1] + '0';
mi[20] = hex_data[16][2] + '0';
mi[21] = hex_data[16][3] + '0';
mi[22] = hex_data[16][4] + '0';
mi[23] = hex_data[16][5] + '0';
mi[24] = hex_data[15][0] + '0';
mi[25] = hex_data[15][1] + '0';
mi[26] = hex_data[15][2] + '0';
mi[27] = hex_data[15][3] + '0';
mi[28] = hex_data[15][4] + '0';
mi[29] = hex_data[15][5] + '0';
mi[30] = hex_data[14][0] + '0';
mi[31] = hex_data[14][1] + '0';
mi[32] = hex_data[14][2] + '0';
mi[33] = hex_data[14][3] + '0';
mi[34] = hex_data[14][4] + '0';
mi[35] = hex_data[14][5] + '0';
mi[36] = hex_data[13][0] + '0';
mi[37] = hex_data[13][1] + '0';
mi[38] = hex_data[13][2] + '0';
mi[39] = hex_data[13][3] + '0';
mi[40] = hex_data[13][4] + '0';
mi[41] = hex_data[13][5] + '0';
mi[42] = hex_data[12][0] + '0';
mi[43] = hex_data[12][1] + '0';
mi[44] = hex_data[12][2] + '0';
mi[45] = hex_data[12][3] + '0';
mi[46] = hex_data[12][4] + '0';
mi[47] = hex_data[12][5] + '0';
mi[48] = hex_data[11][0] + '0';
mi[49] = hex_data[11][1] + '0';
mi[50] = hex_data[11][2] + '0';
mi[51] = hex_data[11][3] + '0';
mi[52] = hex_data[11][4] + '0';
mi[53] = hex_data[11][5] + '0';
mi[54] = hex_data[10][0] + '0';
mi[55] = hex_data[10][1] + '0';
mi[56] = hex_data[10][2] + '0';
mi[57] = hex_data[10][3] + '0';
mi[58] = hex_data[10][4] + '0';
mi[59] = hex_data[10][5] + '0';
mi[60] = hex_data[ 9][0] + '0';
mi[61] = hex_data[ 9][1] + '0';
mi[62] = hex_data[ 9][2] + '0';
mi[63] = hex_data[ 9][3] + '0';
mi[64] = hex_data[ 9][4] + '0';
mi[65] = hex_data[ 9][5] + '0';
mi[66] = hex_data[ 8][0] + '0';
mi[67] = hex_data[ 8][1] + '0';
mi[68] = hex_data[ 8][2] + '0';
mi[69] = hex_data[ 8][3] + '0';
mi[70] = hex_data[ 8][4] + '0';
mi[71] = hex_data[ 8][5] + '0';
mfid[0] = hex_data[ 7][0] + '0';
mfid[1] = hex_data[ 7][1] + '0';
mfid[2] = hex_data[ 7][2] + '0';
mfid[3] = hex_data[ 7][3] + '0';
mfid[4] = hex_data[ 7][4] + '0';
mfid[5] = hex_data[ 7][5] + '0';
mfid[6] = hex_data[ 6][0] + '0';
mfid[7] = hex_data[ 6][1] + '0';
algid[0] = hex_data[ 6][2] + '0'; // The important algorithm ID. This indicates whether the data is
algid[1] = hex_data[ 6][3] + '0'; // encrypted and if so what is the encryption algorithm used.
algid[2] = hex_data[ 6][4] + '0'; // A code 0x80 here means that the data is unencrypted.
algid[3] = hex_data[ 6][5] + '0';
algid[4] = hex_data[ 5][0] + '0';
algid[5] = hex_data[ 5][1] + '0';
algid[6] = hex_data[ 5][2] + '0';
algid[7] = hex_data[ 5][3] + '0';
kid[ 0] = hex_data[ 5][4] + '0';
kid[ 1] = hex_data[ 5][5] + '0';
kid[ 2] = hex_data[ 4][0] + '0'; // The encryption key ID
kid[ 3] = hex_data[ 4][1] + '0';
kid[ 4] = hex_data[ 4][2] + '0';
kid[ 5] = hex_data[ 4][3] + '0';
kid[ 6] = hex_data[ 4][4] + '0';
kid[ 7] = hex_data[ 4][5] + '0';
kid[ 8] = hex_data[ 3][0] + '0';
kid[ 9] = hex_data[ 3][1] + '0';
kid[10] = hex_data[ 3][2] + '0';
kid[11] = hex_data[ 3][3] + '0';
kid[12] = hex_data[ 3][4] + '0';
kid[13] = hex_data[ 3][5] + '0';
kid[14] = hex_data[ 2][0] + '0';
kid[15] = hex_data[ 2][1] + '0';
tgid[ 0] = hex_data[ 2][2] + '0'; // Talk group ID
tgid[ 1] = hex_data[ 2][3] + '0';
tgid[ 2] = hex_data[ 2][4] + '0';
tgid[ 3] = hex_data[ 2][5] + '0';
tgid[ 4] = hex_data[ 1][0] + '0';
tgid[ 5] = hex_data[ 1][1] + '0';
tgid[ 6] = hex_data[ 1][2] + '0';
tgid[ 7] = hex_data[ 1][3] + '0';
tgid[ 8] = hex_data[ 1][4] + '0';
tgid[ 9] = hex_data[ 1][5] + '0';
tgid[10] = hex_data[ 0][0] + '0';
tgid[11] = hex_data[ 0][1] + '0';
tgid[12] = hex_data[ 0][2] + '0';
tgid[13] = hex_data[ 0][3] + '0';
tgid[14] = hex_data[ 0][4] + '0';
tgid[15] = hex_data[ 0][5] + '0';
state->p25kid = strtol(kid, NULL, 2);
skipDibit (opts, state, 5);
status = getDibit (opts, state);
//TODO: Do something useful with the status bits...
if (opts->p25enc == 1)
{
algidhex = strtol (algid, NULL, 2);
kidhex = strtol (kid, NULL, 2);
printf ("mi: %s algid: $%x kid: $%x\n", mi, algidhex, kidhex);
}
if (opts->p25lc == 1)
{
printf ("mfid: %s tgid: %s ", mfid, tgid);
if (opts->p25tg == 0)
{
printf ("\n");
}
}
j = 0;
if (strcmp (mfid, "10010000") == 0)
{
for (i = 4; i < 16; i++)
{
if (state->tgcount < 24)
{
state->tg[state->tgcount][j] = tgid[i];
}
tmpstr[j] = tgid[i];
j++;
}
tmpstr[12] = '0';
tmpstr[13] = '0';
tmpstr[14] = '0';
tmpstr[15] = '0';
}
else
{
for (i = 0; i < 16; i++)
{
if (state->tgcount < 24)
{
state->tg[state->tgcount][j] = tgid[i];
}
tmpstr[j] = tgid[i];
j++;
}
}
tmpstr[16] = 0;
talkgroup = strtol (tmpstr, NULL, 2);
state->lasttg = talkgroup;
if (state->tgcount < 24)
{
state->tgcount = state->tgcount + 1;
}
if (opts->p25tg == 1)
{
printf ("tg: %li\n", talkgroup);
}
}
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