mrtk_l6.c

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/*------------------------------------------------------------------------------
 * mrtk_l6.c : QZSS L6 frame header parsing and service classification
 *
 * Copyright (C) 2026 H.SHIONO (MRTKLIB Project)
 *
 * SPDX-License-Identifier: BSD-2-Clause
 *----------------------------------------------------------------------------*/
#include "mrtklib/mrtk_l6.h"
 
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
/* nominal L6 PRN assignments (see l6_prn_info_t). MADOCA iono regions:
 * PRN 200 Philippines/Indonesia/western Australia, PRN 201 Japan/eastern
 * Australia. */
static const l6_prn_info_t l6_prn_table[] = {
    {193, "QZS1", 0, L6_SVC_CLAS, -1, 0},         {194, "QZS2", 0, L6_SVC_CLAS, -1, 204},
    {195, "QZS4", 0, L6_SVC_CLAS, -1, 205},       {196, "QZS1R", 0, L6_SVC_CLAS, -1, 206},
    {197, "QZS5", 0, L6_SVC_CLAS, -1, 207},       {199, "QZS3", 0, L6_SVC_CLAS, -1, 209},
    {200, "QZS6", 0, L6_SVC_MADOCA_IONO, 0, 210}, {201, "QZS7", 0, L6_SVC_MADOCA_IONO, 1, 211},
    {204, "QZS2", 1, L6_SVC_MADOCA, -1, 194},     {205, "QZS4", 1, L6_SVC_MADOCA, -1, 195},
    {206, "QZS1R", 1, L6_SVC_MADOCA, -1, 196},    {207, "QZS5", 1, L6_SVC_MADOCA, -1, 197},
    {209, "QZS3", 1, L6_SVC_MADOCA, -1, 199},     {210, "QZS6", 1, L6_SVC_MADOCA, -1, 200},
    {211, "QZS7", 1, L6_SVC_MADOCA, -1, 201},
};
 
extern int l6_is_null(const uint8_t* frame) {
    int i;
 
    if (frame[5] != 0 || !(frame[6] & 0x80)) {
        return 0;
    }
    /* byte 6 = alert bit + first 7 data bits "0101010"b = 0xAA */
    for (i = 6; i < L6_FRAME_LEN; i++) {
        if (frame[i] != 0xAA) {
            return 0;
        }
    }
    return 1;
}
 
extern int l6_parse_header(const uint8_t* frame, l6_header_t* h) {
    h->preamble = ((uint32_t)frame[0] << 24) | ((uint32_t)frame[1] << 16) | ((uint32_t)frame[2] << 8) | frame[3];
    h->prn = frame[4];
    h->msgid = frame[5];
    h->vid = (h->msgid >> 5) & 0x07;
    h->fac = (h->msgid >> 3) & 0x03;
    h->ptn = (h->msgid >> 1) & 0x03;
    h->csid = (h->msgid >> 2) & 0x01;
    h->anme = (h->msgid >> 1) & 0x01;
    h->sf_ind = h->msgid & 0x01;
    h->alert = (frame[6] >> 7) & 0x01;
 
    if (h->preamble != L6_PREAMBLE) {
        h->svc = L6_SVC_UNKNOWN;
        return 0;
    }
    if (l6_is_null(frame)) {
        h->svc = L6_SVC_NULL;
    } else if (h->vid == L6_VID_CLAS) {
        h->svc = L6_SVC_CLAS;
    } else if (h->vid == L6_VID_MADOCA) {
        h->svc = h->csid ? L6_SVC_MADOCA_IONO : L6_SVC_MADOCA;
    } else if (h->vid == L6_VID_QZNMA) {
        h->svc = L6_SVC_QZNMA;
    } else {
        h->svc = L6_SVC_UNKNOWN;
    }
    return 1;
}
 
extern const l6_prn_info_t* l6_prn_info(int prn) {
    size_t i;
 
    for (i = 0; i < sizeof(l6_prn_table) / sizeof(l6_prn_table[0]); i++) {
        if (l6_prn_table[i].prn == prn) {
            return l6_prn_table + i;
        }
    }
    return NULL;
}
 
extern int l6_service_expected(const l6_header_t* h) {
    const l6_prn_info_t* info = l6_prn_info(h->prn);
 
    if (h->svc == L6_SVC_NULL) {
        return 1;
    }
    if (!info) {
        return 0;
    }
    if (info->l6e) {
        return h->svc == L6_SVC_MADOCA || h->svc == L6_SVC_QZNMA;
    }
    return h->svc == info->svc;
}
 
extern l6_file_type_t l6_file_type(const char* file) {
    static const char* const ext[] = {".l6", ".l6d", ".l6e"};
    const char* p = strrchr(file, '.');
    size_t i, k;
 
    if (!p) {
        return L6_FILE_NONE;
    }
    for (i = 0; i < sizeof(ext) / sizeof(ext[0]); i++) {
        for (k = 0; p[k] && ext[i][k]; k++) {
            char c = p[k] >= 'A' && p[k] <= 'Z' ? (char)(p[k] - 'A' + 'a') : p[k];
            if (c != ext[i][k]) break;
        }
        if (!p[k] && !ext[i][k]) {
            return (l6_file_type_t)(L6_FILE_L6 + i);
        }
    }
    return L6_FILE_NONE;
}
 
extern l6_service_t l6_file_service(const char* file) {
    l6_service_t svc = L6_SVC_UNKNOWN;
    l6_header_t hdr;
    uint8_t* buf;
    FILE* fp;
    size_t n, i, keep;
 
    if (!(fp = fopen(file, "rb"))) {
        return L6_SVC_UNKNOWN;
    }
    if (!(buf = (uint8_t*)malloc(L6_FILE_SCAN_BYTES + L6_FRAME_LEN))) {
        fclose(fp);
        return L6_SVC_UNKNOWN;
    }
    /* read in chunks until the first classifiable frame or the end of the
     * file: a long run of null messages must not hide the service. "keep"
     * bytes of the previous chunk are carried over so a frame that straddles
     * two chunks is still seen. */
    keep = 0;
    while (svc == L6_SVC_UNKNOWN && (n = fread(buf + keep, 1, L6_FILE_SCAN_BYTES, fp)) > 0) {
        n += keep;
        for (i = 0; i + L6_FRAME_LEN <= n; i++) {
            if (!l6_parse_header(buf + i, &hdr)) {
                continue;
            }
            if (hdr.svc != L6_SVC_NULL && hdr.svc != L6_SVC_UNKNOWN) {
                svc = hdr.svc;
                break;
            }
            i += L6_FRAME_LEN - 1; /* null / reserved frame: skip to the next one */
        }
        if (svc != L6_SVC_UNKNOWN) {
            break;
        }
        keep = n - i < L6_FRAME_LEN ? n - i : 0; /* partial frame at the end */
        memmove(buf, buf + n - keep, keep);
    }
    fclose(fp);
    free(buf);
    return svc;
}
 
extern const char* l6_service_name(l6_service_t svc) {
    switch (svc) {
        case L6_SVC_NULL:
            return "NULL";
        case L6_SVC_CLAS:
            return "CLAS";
        case L6_SVC_MADOCA:
            return "MADOCA";
        case L6_SVC_MADOCA_IONO:
            return "MADOCA-IONO";
        case L6_SVC_QZNMA:
            return "QZNMA";
        default:
            return "UNKNOWN";
    }
}