kopia lustrzana https://github.com/cyoung/stratux
94 wiersze
2.8 KiB
C
94 wiersze
2.8 KiB
C
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//
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// Copyright 2015, Oliver Jowett <oliver@mutability.co.uk>
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//
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// This file is free software: you may copy, redistribute and/or modify it
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// under the terms of the GNU General Public License as published by the
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// Free Software Foundation, either version 2 of the License, or (at your
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// option) any later version.
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//
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// This file is distributed in the hope that it will be useful, but
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// WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program. If not, see <http://www.gnu.org/licenses/>.
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#include <stdio.h>
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#include <stdlib.h>
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#include <stdint.h>
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#include <string.h>
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#include <math.h>
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#include <unistd.h>
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#include "uat.h"
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#include "fec/rs.h"
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static void *rs_uplink;
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static void *rs_adsb_short;
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static void *rs_adsb_long;
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#define UPLINK_POLY 0x187
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#define ADSB_POLY 0x187
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void init_fec(void)
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{
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rs_adsb_short = init_rs_char(8, /* gfpoly */ ADSB_POLY, /* fcr */ 120, /* prim */ 1, /* nroots */ 12, /* pad */ 225);
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rs_adsb_long = init_rs_char(8, /* gfpoly */ ADSB_POLY, /* fcr */ 120, /* prim */ 1, /* nroots */ 14, /* pad */ 207);
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rs_uplink = init_rs_char(8, /* gfpoly */ UPLINK_POLY, /* fcr */ 120, /* prim */ 1, /* nroots */ 20, /* pad */ 163);
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}
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int correct_adsb_frame(uint8_t *to, int *rs_errors)
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{
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// Try decoding as a Long UAT.
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// We rely on decode_rs_char not modifying the data if there were
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// uncorrectable errors.
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int n_corrected = decode_rs_char(rs_adsb_long, to, NULL, 0);
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if (n_corrected >= 0 && n_corrected <= 7 && (to[0]>>3) != 0) {
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// Valid long frame.
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*rs_errors = n_corrected;
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return 2;
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}
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// Retry as Basic UAT
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n_corrected = decode_rs_char(rs_adsb_short, to, NULL, 0);
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if (n_corrected >= 0 && n_corrected <= 6 && (to[0]>>3) == 0) {
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// Valid short frame
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*rs_errors = n_corrected;
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return 1;
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}
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// Failed.
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*rs_errors = 9999;
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return -1;
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}
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int correct_uplink_frame(uint8_t *from, uint8_t *to, int *rs_errors)
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{
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int block;
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int total_corrected = 0;
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for (block = 0; block < UPLINK_FRAME_BLOCKS; ++block) {
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int i, n_corrected;
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uint8_t *blockdata = &to[block * UPLINK_BLOCK_DATA_BYTES];
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for (i = 0; i < UPLINK_BLOCK_BYTES; ++i)
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blockdata[i] = from[i * UPLINK_FRAME_BLOCKS + block];
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// error-correct in place
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n_corrected = decode_rs_char(rs_uplink, blockdata, NULL, 0);
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if (n_corrected < 0 || n_corrected > 10) {
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// Failed
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*rs_errors = 9999;
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return -1;
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}
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total_corrected += n_corrected;
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// next block (if there is one) will overwrite the ECC bytes.
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}
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*rs_errors = total_corrected;
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return 1;
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}
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