gpsd/subframe.c

/* subframe.c -- interpret satellite subframe data.
 *
 * This file is Copyright 2010 by the GPSD project
 * SPDX-License-Identifier: BSD-2-clause
 */

#include "gpsd_config.h"  /* must be before all includes */

#include <math.h>

#include "gpsd.h"

/* convert unsigned to signed */
#define uint2int( u, bit) ( (u & (1<<(bit-1))) ? u - (1<<bit) : u)

gps_mask_t gpsd_interpret_subframe_raw(struct gps_device_t *session,
                                       unsigned int tSVID, uint32_t words[])
{
    unsigned int i;
    uint8_t preamble;

    if (session->subframe_count++ == 0) {
        speed_t speed = gpsd_get_speed(session);

        if (speed < 38400)
            GPSD_LOG(LOG_WARN, &session->context->errout,
                     "speed less than 38,400 may cause data lag and "
                     "loss of functionality\n");
    }

    /*
     * This function assumes an array of 10 ints, each of which carries
     * a raw 30-bit GPS word use your favorite search engine to find the
     * latest version of the specification: IS-GPS-200.
     *
     * Each raw 30-bit word is made of 24 data bits and 6 parity bits. The
     * raw word and transport word are emitted from the GPS MSB-first and
     * right justified. In other words, masking the raw word against 0x3f
     * will return just the parity bits. Masking with 0x3fffffff and shifting
     * 6 bits to the right returns just the 24 data bits. The top two bits
     * (b31 and b30) are undefined; chipset designers may store copies of
     * the bits D29* and D30* here to aid parity checking.
     *
     * Since bits D29* and D30* are not available in word 0, it is tested for
     * a known preamble to help check its validity and determine whether the
     * word is inverted.
     *
     */
    GPSD_LOG(LOG_DATA, &session->context->errout,
             "50B: gpsd_interpret_subframe_raw: "
             "%08x %08x %08x %08x %08x %08x %08x %08x %08x %08x\n",
             words[0], words[1], words[2], words[3], words[4],
             words[5], words[6], words[7], words[8], words[9]);

    preamble = (uint8_t)((words[0] >> 22) & 0xFF);
    if (preamble == 0x8b) {     /* preamble is inverted */
        words[0] ^= 0x3fffffc0; /* invert */
    } else if (preamble != 0x74) {
        /* strangely this is very common, so don't log it */
        GPSD_LOG(LOG_DATA, &session->context->errout,
                 "50B: gpsd_interpret_subframe_raw: bad preamble 0x%x\n",
                 preamble);
        return 0;
    }
    words[0] = (words[0] >> 6) & 0xffffff;

    for (i = 1; i < 10; i++) {
        int invert;
        uint32_t parity;
        /* D30* says invert */
        invert = (words[i] & 0x40000000) ? 1 : 0;
        /* inverted data, invert it back */
        if (invert) {
            words[i] ^= 0x3fffffc0;
        }
        parity = (uint32_t)isgps_parity((isgps30bits_t)words[i]);
        if (parity != (words[i] & 0x3f)) {
            GPSD_LOG(LOG_DATA, &session->context->errout,
                     "50B: gpsd_interpret_subframe_raw parity fail "
                     "words[%d] 0x%x != 0x%x\n",
                     i, parity, (words[i] & 0x1));
            return 0;
        }
        words[i] = (words[i] >> 6) & 0xffffff;
    }

    return gpsd_interpret_subframe(session, tSVID, words);
}

/* you can find up to date almanac data for comparison here:
 * https://gps.afspc.af.mil/gps/Current/current.alm
 */
static void subframe_almanac(const struct gpsd_errout_t *errout,
                             uint8_t tSVID, uint32_t words[],
                             uint8_t subframe, uint8_t sv,
                             uint8_t data_id,
                             struct almanac_t *almp)
{
    almp->sv     = sv; /* ignore the 0 sv problem for now */
    almp->e      = ( words[2] & 0x00FFFF);
    almp->d_eccentricity  = pow(2.0,-21) * almp->e;
    /* careful, each SV can have more than 2 toa's active at the same time
     * you can not just store one or two almanacs for each sat */
    almp->toa      = ((words[3] >> 16) & 0x0000FF);
    almp->l_toa    = almp->toa << 12;
    almp->deltai   = ( words[3] & 0x00FFFF);
    almp->d_deltai = pow(2.0, -19) * almp->deltai;
    almp->Omegad   = ((words[4] >>  8) & 0x00FFFF);
    almp->d_Omegad = pow(2.0, -38) * almp->Omegad;
    almp->svh      = ( words[4] & 0x0000FF);
    almp->sqrtA    = ( words[5] & 0xFFFFFF);
    almp->d_sqrtA  = pow(2.0,-11) * almp->sqrtA;
    almp->Omega0   = ( words[6] & 0xFFFFFF);
    almp->Omega0   = uint2int(almp->Omega0, 24);
    almp->d_Omega0 = pow(2.0, -23) * almp->Omega0;
    almp->omega    = ( words[7] & 0xFFFFFF);
    almp->omega    = uint2int(almp->omega, 24);
    almp->d_omega  = pow(2.0, -23) * almp->omega;
    almp->M0       = ( words[8] & 0x00FFFFFF);
    almp->M0       = uint2int(almp->M0, 24);
    /* if you want radians, multiply by GPS_PI, but we do semi-circles
     * to match IS-GPS-200E */
    almp->d_M0     = pow(2.0,-23) * almp->M0;
    almp->af1      = ((words[9] >>  5) & 0x0007FF);
    almp->af1      = (short)uint2int(almp->af1, 11);
    almp->d_af1    = pow(2.0,-38) * almp->af1;
    almp->af0      = ((words[9] >> 16) & 0x0000FF);
    almp->af0    <<= 3;
    almp->af0     |= ((words[9] >>  2) & 0x000007);
    almp->af0      = (short)uint2int(almp->af0, 11);
    almp->d_af0    = pow(2.0,-20) * almp->af0;
    GPSD_LOG(LOG_PROG, errout,
             "50B: SF:%d SV:%2u TSV:%2u data_id %d e:%g toa:%lu "
             "deltai:%.10e Omegad:%.5e svh:%u sqrtA:%.10g Omega0:%.10e "
             "omega:%.10e M0:%.11e af0:%.5e af1:%.5e\n",
             subframe, almp->sv, tSVID, data_id,
             almp->d_eccentricity,
             almp->l_toa,
             almp->d_deltai,
             almp->d_Omegad,
             almp->svh,
             almp->d_sqrtA,
             almp->d_Omega0,
             almp->d_omega,
             almp->d_M0,
             almp->d_af0,
             almp->d_af1);
}

gps_mask_t gpsd_interpret_subframe(struct gps_device_t *session,
                             unsigned int tSVID, uint32_t words[])
{
    /*
     * Heavy black magic begins here!
     *
     * A description of how to decode these bits is at
     * <http://home-2.worldonline.nl/~samsvl/nav2eu.htm>
     *
     * We're mostly looking for subframe 4 page 18 word 9, the leap second
     * correction. This functions assumes an array of words without parity
     * or inversion (inverted word 0 is OK). It may be called directly by a
     * driver if the chipset emits acceptable data.
     *
     * To date this code has been tested on iTrax, SiRF and ublox.
     */
    /* FIXME!! I really doubt this is Big Endian compatible */
    uint8_t preamble;
    struct subframe_t *subp = &session->gpsdata.subframe;

    GPSD_LOG(LOG_DATA, &session->context->errout,
             "50B: gpsd_interpret_subframe: (%d) "
             "%06x %06x %06x %06x %06x %06x %06x %06x %06x %06x\n",
             tSVID, words[0], words[1], words[2], words[3], words[4],
             words[5], words[6], words[7], words[8], words[9]);

    preamble = (uint8_t)((words[0] >> 16) & 0x0FF);
    if (preamble == 0x8b) {
        /* somehow missed an inversion */
        preamble ^= 0xff;
        words[0] ^= 0xffffff;
    }
    if (preamble != 0x74) {
        GPSD_LOG(LOG_WARN, &session->context->errout,
                 "50B: gpsd_interpret_subframe bad preamble: "
                 "0x%x header 0x%x\n",
                 preamble, words[0]);
        return 0;
    }
    subp->integrity = (bool)((words[0] >> 1) & 0x01);
    /* The subframe ID is in the Hand Over Word (page 80) */
    subp->TOW17 = ((words[1] >> 7) & 0x01FFFF);
    subp->l_TOW17 = (long)(subp->TOW17 * 6);
    subp->tSVID = (uint8_t)tSVID;
    subp->subframe_num = ((words[1] >> 2) & 0x07);
    subp->alert = (bool)((words[1] >> 6) & 0x01);
    subp->antispoof = (bool)((words[1] >> 6) & 0x01);
    GPSD_LOG(LOG_PROG, &session->context->errout,
             "50B: SF:%d SV:%2u TOW17:%7lu Alert:%u AS:%u IF:%d\n",
             subp->subframe_num, subp->tSVID, subp->l_TOW17,
             (unsigned)subp->alert, (unsigned)subp->antispoof,
             (unsigned)subp->integrity);
    /*
     * Consult the latest revision of IS-GPS-200 for the mapping
     * between magic SVIDs and pages.
     */
    subp->pageid  = (words[2] >> 16) & 0x00003F; /* only in frames 4 & 5 */
    subp->data_id = (words[2] >> 22) & 0x3;      /* only in frames 4 & 5 */
    subp->is_almanac = 0;

    switch (subp->subframe_num) {
    case 1:
        /* subframe 1: clock parameters for transmitting SV */
        /* get Week Number (WN) from subframe 1 */
        /*
         * This only extracts 10 bits of GPS week.
         * 13 bits are available in the extension CNAV message,
         * which we don't decode yet because we don't know
         * of any receiver that reports it.
         */
        session->context->gps_week =
            (unsigned short)((words[2] >> 14) & 0x03ff);
        subp->sub1.WN   = (uint16_t)session->context->gps_week;
        subp->sub1.l2   = (uint8_t)((words[2] >> 12) & 0x000003); /* L2 Code */
        /* URA Index */
        subp->sub1.ura  = (unsigned int)((words[2] >>  8) & 0x00000F);
        /* SV health */
        subp->sub1.hlth = (unsigned int)((words[2] >>  2) & 0x00003F);
        subp->sub1.IODC = (words[2] & 0x000003); /* IODC 2 MSB */
        subp->sub1.l2p  = ((words[3] >> 23) & 0x000001); /* L2 P flag */
        subp->sub1.Tgd  = (int8_t)( words[6] & 0x0000FF);
        subp->sub1.d_Tgd  = pow(2.0, -31) * (int)subp->sub1.Tgd;
        subp->sub1.toc  = ( words[7] & 0x00FFFF);
        subp->sub1.l_toc = (long)subp->sub1.toc  << 4;
        subp->sub1.af2  = (int8_t)((words[8] >> 16) & 0x0FF);
        subp->sub1.d_af2  = pow(2.0, -55) * (int)subp->sub1.af2;
        subp->sub1.af1  = (int16_t)( words[8] & 0x00FFFF);
        subp->sub1.d_af1  = pow(2.0, -43) * subp->sub1.af1;
        subp->sub1.af0  = (int32_t)((words[9] >>  2) & 0x03FFFFF);
        subp->sub1.af0  = uint2int(subp->sub1.af0, 22);
        subp->sub1.d_af0  = pow(2.0, -31) * subp->sub1.af0;
        subp->sub1.IODC <<= 8;
        subp->sub1.IODC |= ((words[7] >> 16) & 0x00FF);
        GPSD_LOG(LOG_PROG, &session->context->errout,
                 "50B: SF:1 SV:%2u WN:%4u IODC:%4u"
                 " L2:%u ura:%u hlth:%u L2P:%u Tgd:%g toc:%lu af2:%.4g"
                 " af1:%.6e af0:%.7e\n",
                 subp->tSVID,
                 subp->sub1.WN,
                 subp->sub1.IODC,
                 subp->sub1.l2,
                 subp->sub1.ura,
                 subp->sub1.hlth,
                 subp->sub1.l2p,
                 subp->sub1.d_Tgd,
                 subp->sub1.l_toc,
                 subp->sub1.d_af2,
                 subp->sub1.d_af1,
                 subp->sub1.d_af0);
        break;
    case 2:
        /* subframe 2: ephemeris for transmitting SV */
        subp->sub2.IODE   = ((words[2] >> 16) & 0x00FF);
        subp->sub2.Crs    = (int16_t)( words[2] & 0x00FFFF);
        subp->sub2.d_Crs  = pow(2.0,-5) * subp->sub2.Crs;
        subp->sub2.deltan = (int16_t)((words[3] >>  8) & 0x00FFFF);
        subp->sub2.d_deltan  = pow(2.0,-43) * subp->sub2.deltan;
        subp->sub2.M0     = (int32_t)( words[3] & 0x0000FF);
        subp->sub2.M0   <<= 24;
        subp->sub2.M0    |= ( words[4] & 0x00FFFFFF);
        subp->sub2.d_M0   = pow(2.0,-31) * subp->sub2.M0 * GPS_PI;
        subp->sub2.Cuc    = (int16_t)((words[5] >>  8) & 0x00FFFF);
        subp->sub2.d_Cuc  = pow(2.0,-29) * subp->sub2.Cuc;
        subp->sub2.e      = ( words[5] & 0x0000FF);
        subp->sub2.e    <<= 24;
        subp->sub2.e     |= ( words[6] & 0x00FFFFFF);
        subp->sub2.d_eccentricity  = pow(2.0,-33) * subp->sub2.e;
        subp->sub2.Cus    = (int16_t)((words[7] >>  8) & 0x00FFFF);
        subp->sub2.d_Cus  = pow(2.0,-29) * subp->sub2.Cus;
        subp->sub2.sqrtA  = ( words[7] & 0x0000FF);
        subp->sub2.sqrtA <<= 24;
        subp->sub2.sqrtA |= ( words[8] & 0x00FFFFFF);
        subp->sub2.d_sqrtA = pow(2.0, -19) * subp->sub2.sqrtA;
        subp->sub2.toe    = ((words[9] >>  8) & 0x00FFFF);
        subp->sub2.l_toe  = (long)(subp->sub2.toe << 4);
        subp->sub2.fit    = ((words[9] >>  7) & 0x000001);
        subp->sub2.AODO   = ((words[9] >>  2) & 0x00001F);
        subp->sub2.u_AODO   = subp->sub2.AODO * 900;
        GPSD_LOG(LOG_PROG, &session->context->errout,
                 "50B: SF:2 SV:%2u IODE:%3u Crs:%.6e deltan:%.6e "
                 "M0:%.11e Cuc:%.6e e:%f Cus:%.6e sqrtA:%.11g "
                 "toe:%lu FIT:%u AODO:%5u\n",
                 subp->tSVID,
                 subp->sub2.IODE,
                 subp->sub2.d_Crs,
                 subp->sub2.d_deltan,
                 subp->sub2.d_M0,
                 subp->sub2.d_Cuc,
                 subp->sub2.d_eccentricity,
                 subp->sub2.d_Cus,
                 subp->sub2.d_sqrtA,
                 subp->sub2.l_toe,
                 subp->sub2.fit,
                 subp->sub2.u_AODO);
        break;
    case 3:
        /* subframe 3: ephemeris for transmitting SV */
        subp->sub3.Cic      = (int16_t)((words[2] >>  8) & 0x00FFFF);
        subp->sub3.d_Cic    = pow(2.0, -29) * subp->sub3.Cic;
        subp->sub3.Omega0   = (int32_t)(words[2] & 0x0000FF);
        subp->sub3.Omega0 <<= 24;
        subp->sub3.Omega0  |= ( words[3] & 0x00FFFFFF);
        subp->sub3.d_Omega0 = pow(2.0, -31) * subp->sub3.Omega0;
        subp->sub3.Cis      = (int16_t)((words[4] >>  8) & 0x00FFFF);
        subp->sub3.d_Cis    = pow(2.0, -29) * subp->sub3.Cis;
        subp->sub3.i0       = (int32_t)(words[4] & 0x0000FF);
        subp->sub3.i0     <<= 24;
        subp->sub3.i0      |= ( words[5] & 0x00FFFFFF);
        subp->sub3.d_i0     = pow(2.0, -31) * subp->sub3.i0;
        subp->sub3.Crc      = (int16_t)((words[6] >>  8) & 0x00FFFF);
        subp->sub3.d_Crc    = pow(2.0, -5) * subp->sub3.Crc;
        subp->sub3.omega    = (int32_t)(words[6] & 0x0000FF);
        subp->sub3.omega  <<= 24;
        subp->sub3.omega   |= ( words[7] & 0x00FFFFFF);
        subp->sub3.d_omega  = pow(2.0, -31) * subp->sub3.omega;
        subp->sub3.Omegad   = (int32_t)(words[8] & 0x00FFFFFF);
        subp->sub3.Omegad   = uint2int(subp->sub3.Omegad, 24);
        subp->sub3.d_Omegad = pow(2.0, -43) * subp->sub3.Omegad;
        subp->sub3.IODE     = ((words[9] >> 16) & 0x0000FF);
        subp->sub3.IDOT     = (int16_t)((words[9] >>  2) & 0x003FFF);
        subp->sub3.IDOT     = uint2int(subp->sub3.IDOT, 14);
        subp->sub3.d_IDOT   = pow(2.0, -43) * subp->sub3.IDOT;
        GPSD_LOG(LOG_PROG, &session->context->errout,
                 "50B: SF:3 SV:%2u IODE:%3u I IDOT:%.6g Cic:%.6e Omega0:%.11e "
                 " Cis:%.7g i0:%.11e Crc:%.7g omega:%.11e Omegad:%.6e\n",
                 subp->tSVID, subp->sub3.IODE, subp->sub3.d_IDOT,
                 subp->sub3.d_Cic, subp->sub3.d_Omega0, subp->sub3.d_Cis,
                 subp->sub3.d_i0, subp->sub3.d_Crc, subp->sub3.d_omega,
                 subp->sub3.d_Omegad );
        break;
    case 4:
        {
            int i = 0;   /* handy loop counter */
            int sv = -2;
            switch (subp->pageid) {
            case 0:
                /* almanac for dummy sat 0, which is same as transmitting sat */
                sv = 0;
                break;
            case 1:
            case 6:
            case 11:
            case 16:
            case 21:
            case 57:
                /* for some inscutable reason these pages are all sent
                 * as page 57, IS-GPS-200E Table 20-V */
                break;
            case 12:
            case 24:
            case 62:
                /* for some inscrutable reason these pages are all sent
                 * as page 62, IS-GPS-200E Table 20-V */
                break;
            case 14:
            case 53:
                /* for some inscrutable reason page 14 is sent
                 * as page 53, IS-GPS-200E Table 20-V */
                break;
            case 15:
            case 54:
                /* for some inscrutable reason page 15 is sent
                 * as page 54, IS-GPS-200E Table 20-V */
                break;
            case 19:
                /* for some inscrutable reason page 20 is sent
                 * as page 58, IS-GPS-200E Table 20-V */
                /* reserved page */
                break;
            case 20:
                /* for some inscrutable reason page 20 is sent
                 * as page 59, IS-GPS-200E Table 20-V */
                /* reserved page */
                break;
            case 22:
            case 60:
                /* for some inscrutable reason page 22 is sent
                 * as page 60, IS-GPS-200E Table 20-V */
                /* reserved page */
                break;
            case 23:
            case 61:
                /* for some inscrutable reason page 23 is sent
                 * as page 61, IS-GPS-200E Table 20-V */
                /* reserved page */
                break;

            /* almanac data for SV 25 through 32 respectively; */
            case 2:
                sv = 25;
                break;
            case 3:
                sv = 26;
                break;
            case 4:
                sv = 27;
                break;
            case 5:
                sv = 28;
                break;
            case 7:
                sv = 29;
                break;
            case 8:
                sv = 30;
                break;
            case 9:
                sv = 31;
                break;
            case 10:
                sv = 32;
                break;

            case 13:
            case 52:
                /* NMCT */
                sv = -1;
                subp->sub4_13.ai = (unsigned char)((words[2] >> 22) & 0x000003);
                subp->sub4_13.ERD[1]  = (char)((words[2] >>  8) & 0x00003F);
                subp->sub4_13.ERD[2]  = (char)((words[2] >>  2) & 0x00003F);
                subp->sub4_13.ERD[3]  = (char)((words[2] >>  0) & 0x000003);
                subp->sub4_13.ERD[3] <<= 2;
                subp->sub4_13.ERD[3] |= (char)((words[3] >> 20) & 0x00000F);

                subp->sub4_13.ERD[4]  = (char)((words[3] >> 14) & 0x00003F);
                subp->sub4_13.ERD[5]  = (char)((words[3] >>  8) & 0x00003F);
                subp->sub4_13.ERD[6]  = (char)((words[3] >>  2) & 0x00003F);
                subp->sub4_13.ERD[7]  = (char)((words[3] >>  0) & 0x000003);

                subp->sub4_13.ERD[7] <<= 2;
                subp->sub4_13.ERD[7] |= (char)((words[4] >> 20) & 0x00000F);
                subp->sub4_13.ERD[8]  = (char)((words[4] >> 14) & 0x00003F);
                subp->sub4_13.ERD[9]  = (char)((words[4] >>  8) & 0x00003F);
                subp->sub4_13.ERD[10] = (char)((words[4] >>  2) & 0x00003F);
                subp->sub4_13.ERD[11] = (char)((words[4] >>  0) & 0x00000F);

                subp->sub4_13.ERD[11] <<= 2;
                subp->sub4_13.ERD[11] |= (char)((words[5] >> 20) & 0x00000F);
                subp->sub4_13.ERD[12]  = (char)((words[5] >> 14) & 0x00003F);
                subp->sub4_13.ERD[13]  = (char)((words[5] >>  8) & 0x00003F);
                subp->sub4_13.ERD[14]  = (char)((words[5] >>  2) & 0x00003F);
                subp->sub4_13.ERD[15]  = (char)((words[5] >>  0) & 0x000003);

                subp->sub4_13.ERD[15] <<= 2;
                subp->sub4_13.ERD[15] |= (char)((words[6] >> 20) & 0x00000F);
                subp->sub4_13.ERD[16]  = (char)((words[6] >> 14) & 0x00003F);
                subp->sub4_13.ERD[17]  = (char)((words[6] >>  8) & 0x00003F);
                subp->sub4_13.ERD[18]  = (char)((words[6] >>  2) & 0x00003F);
                subp->sub4_13.ERD[19]  = (char)((words[6] >>  0) & 0x000003);

                subp->sub4_13.ERD[19] <<= 2;
                subp->sub4_13.ERD[19] |= (char)((words[7] >> 20) & 0x00000F);
                subp->sub4_13.ERD[20]  = (char)((words[7] >> 14) & 0x00003F);
                subp->sub4_13.ERD[21]  = (char)((words[7] >>  8) & 0x00003F);
                subp->sub4_13.ERD[22]  = (char)((words[7] >>  2) & 0x00003F);
                subp->sub4_13.ERD[23]  = (char)((words[7] >>  0) & 0x000003);

                subp->sub4_13.ERD[23] <<= 2;
                subp->sub4_13.ERD[23] |= (char)((words[8] >> 20) & 0x00000F);
                subp->sub4_13.ERD[24]  = (char)((words[8] >> 14) & 0x00003F);
                subp->sub4_13.ERD[25]  = (char)((words[8] >>  8) & 0x00003F);
                subp->sub4_13.ERD[26]  = (char)((words[8] >>  2) & 0x00003F);
                subp->sub4_13.ERD[27]  = (char)((words[8] >>  0) & 0x000003);

                subp->sub4_13.ERD[27] <<= 2;
                subp->sub4_13.ERD[27] |= (char)((words[9] >> 20) & 0x00000F);
                subp->sub4_13.ERD[28]  = (char)((words[9] >> 14) & 0x00003F);
                subp->sub4_13.ERD[29]  = (char)((words[9] >>  8) & 0x00003F);
                subp->sub4_13.ERD[30]  = (char)((words[9] >>  2) & 0x00003F);

                for ( i = 1; i < 31; i++ ) {
                    subp->sub4_13.ERD[i]  = uint2int(subp->sub4_13.ERD[i], 6);
                }

                GPSD_LOG(LOG_PROG, &session->context->errout,
                         "50B: SF:4-13 data_id %d ai:%u "
                         "ERD1:%d ERD2:%d ERD3:%d ERD4:%d "
                         "ERD5:%d ERD6:%d ERD7:%d ERD8:%d "
                         "ERD9:%d ERD10:%d ERD11:%d ERD12:%d "
                         "ERD13:%d ERD14:%d ERD15:%d ERD16:%d "
                         "ERD17:%d ERD18:%d ERD19:%d ERD20:%d "
                         "ERD21:%d ERD22:%d ERD23:%d ERD24:%d "
                         "ERD25:%d ERD26:%d ERD27:%d ERD28:%d "
                         "ERD29:%d ERD30:%d\n",
                         subp->data_id, subp->sub4_13.ai,
                         subp->sub4_13.ERD[1], subp->sub4_13.ERD[2],
                         subp->sub4_13.ERD[3], subp->sub4_13.ERD[4],
                         subp->sub4_13.ERD[5], subp->sub4_13.ERD[6],
                         subp->sub4_13.ERD[7], subp->sub4_13.ERD[8],
                         subp->sub4_13.ERD[9], subp->sub4_13.ERD[10],
                         subp->sub4_13.ERD[11], subp->sub4_13.ERD[12],
                         subp->sub4_13.ERD[13], subp->sub4_13.ERD[14],
                         subp->sub4_13.ERD[15], subp->sub4_13.ERD[16],
                         subp->sub4_13.ERD[17], subp->sub4_13.ERD[18],
                         subp->sub4_13.ERD[19], subp->sub4_13.ERD[20],
                         subp->sub4_13.ERD[21], subp->sub4_13.ERD[22],
                         subp->sub4_13.ERD[23], subp->sub4_13.ERD[24],
                         subp->sub4_13.ERD[25], subp->sub4_13.ERD[26],
                         subp->sub4_13.ERD[27], subp->sub4_13.ERD[28],
                         subp->sub4_13.ERD[29], subp->sub4_13.ERD[30]);
                break;

            case 25:
            case 63:
                /* for some inscrutable reason page 25 is sent
                 * as page 63, IS-GPS-200E Table 20-V */
                /* A-S flags/SV configurations for 32 SVs,
                 * plus SV health for SV 25 through 32
                 */

                sv = -1;
                subp->sub4_25.svf[1] = (unsigned char)((words[2] >> 12) & 0x0F);
                subp->sub4_25.svf[2] = (unsigned char)((words[2] >>  8) & 0x0F);
                subp->sub4_25.svf[3] = (unsigned char)((words[2] >>  4) & 0x0F);
                subp->sub4_25.svf[4] = (unsigned char)((words[2] >>  0) & 0x0F);
                subp->sub4_25.svf[5] = (unsigned char)((words[3] >> 20) & 0x0F);
                subp->sub4_25.svf[6] = (unsigned char)((words[3] >> 16) & 0x0F);
                subp->sub4_25.svf[7] = (unsigned char)((words[3] >> 12) & 0x0F);
                subp->sub4_25.svf[8] = (unsigned char)((words[3] >>  8) & 0x0F);
                subp->sub4_25.svf[9] = (unsigned char)((words[3] >>  4) & 0x0F);
                subp->sub4_25.svf[10] = (unsigned char)((words[3] >> 0) & 0x0F);
                subp->sub4_25.svf[11] = (unsigned char)((words[4] >> 20) & 0x0F);
                subp->sub4_25.svf[12] = (unsigned char)((words[4] >> 16) & 0x0F);
                subp->sub4_25.svf[13] = (unsigned char)((words[4] >> 12) & 0x0F);
                subp->sub4_25.svf[14] = (unsigned char)((words[4] >> 8) & 0x0F);
                subp->sub4_25.svf[15] = (unsigned char)((words[4] >> 4) & 0x0F);
                subp->sub4_25.svf[16] = (unsigned char)((words[4] >> 0) & 0x0F);
                subp->sub4_25.svf[17] = (unsigned char)((words[5] >> 20) & 0x0F);
                subp->sub4_25.svf[18] = (unsigned char)((words[5] >> 16) & 0x0F);
                subp->sub4_25.svf[19] = (unsigned char)((words[5] >> 12) & 0x0F);
                subp->sub4_25.svf[20] = (unsigned char)((words[5] >> 8) & 0x0F);
                subp->sub4_25.svf[21] = (unsigned char)((words[5] >> 4) & 0x0F);
                subp->sub4_25.svf[22] = (unsigned char)((words[5] >> 0) & 0x0F);
                subp->sub4_25.svf[23] = (unsigned char)((words[6] >> 20) & 0x0F);
                subp->sub4_25.svf[24] = (unsigned char)((words[6] >> 16) & 0x0F);
                subp->sub4_25.svf[25] = (unsigned char)((words[6] >> 12) & 0x0F);
                subp->sub4_25.svf[26] = (unsigned char)((words[6] >> 8) & 0x0F);
                subp->sub4_25.svf[27] = (unsigned char)((words[6] >> 4) & 0x0F);
                subp->sub4_25.svf[28] = (unsigned char)((words[6] >> 0) & 0x0F);
                subp->sub4_25.svf[29] = (unsigned char)((words[7] >> 20) & 0x0F);
                subp->sub4_25.svf[30] = (unsigned char)((words[7] >> 16) & 0x0F);
                subp->sub4_25.svf[31] = (unsigned char)((words[7] >> 12) & 0x0F);
                subp->sub4_25.svf[32] = (unsigned char)((words[7] >> 8) & 0x0F);

                subp->sub4_25.svhx[0] = ((words[7] >>  0) & 0x00003F);
                subp->sub4_25.svhx[1] = ((words[8] >> 18) & 0x00003F);
                subp->sub4_25.svhx[2] = ((words[8] >> 12) & 0x00003F);
                subp->sub4_25.svhx[3] = ((words[8] >>  6) & 0x00003F);
                subp->sub4_25.svhx[4] = ((words[8] >>  0) & 0x00003F);
                subp->sub4_25.svhx[5] = ((words[9] >> 18) & 0x00003F);
                subp->sub4_25.svhx[6] = ((words[9] >> 12) & 0x00003F);
                subp->sub4_25.svhx[7] = ((words[9] >>  6) & 0x00003F);

                GPSD_LOG(LOG_PROG, &session->context->errout,
                         "50B: SF:4-25 data_id %d "
                         "SV1:%u SV2:%u SV3:%u SV4:%u "
                         "SV5:%u SV6:%u SV7:%u SV8:%u "
                         "SV9:%u SV10:%u SV11:%u SV12:%u "
                         "SV13:%u SV14:%u SV15:%u SV16:%u "
                         "SV17:%u SV18:%u SV19:%u SV20:%u "
                         "SV21:%u SV22:%u SV23:%u SV24:%u "
                         "SV25:%u SV26:%u SV27:%u SV28:%u "
                         "SV29:%u SV30:%u SV31:%u SV32:%u "
                         "SVH25:%u SVH26:%u SVH27:%u SVH28:%u "
                         "SVH29:%u SVH30:%u SVH31:%u SVH32:%u\n",
                         subp->data_id,
                         subp->sub4_25.svf[1],  subp->sub4_25.svf[2],
                         subp->sub4_25.svf[3],  subp->sub4_25.svf[4],
                         subp->sub4_25.svf[5],  subp->sub4_25.svf[6],
                         subp->sub4_25.svf[7],  subp->sub4_25.svf[8],
                         subp->sub4_25.svf[9],  subp->sub4_25.svf[10],
                         subp->sub4_25.svf[11], subp->sub4_25.svf[12],
                         subp->sub4_25.svf[13], subp->sub4_25.svf[14],
                         subp->sub4_25.svf[15], subp->sub4_25.svf[16],
                         subp->sub4_25.svf[17], subp->sub4_25.svf[18],
                         subp->sub4_25.svf[19], subp->sub4_25.svf[20],
                         subp->sub4_25.svf[21], subp->sub4_25.svf[22],
                         subp->sub4_25.svf[23], subp->sub4_25.svf[24],
                         subp->sub4_25.svf[25], subp->sub4_25.svf[26],
                         subp->sub4_25.svf[27], subp->sub4_25.svf[28],
                         subp->sub4_25.svf[29], subp->sub4_25.svf[30],
                         subp->sub4_25.svf[31], subp->sub4_25.svf[32],
                         subp->sub4_25.svhx[0], subp->sub4_25.svhx[1],
                         subp->sub4_25.svhx[2], subp->sub4_25.svhx[3],
                         subp->sub4_25.svhx[4], subp->sub4_25.svhx[5],
                         subp->sub4_25.svhx[6], subp->sub4_25.svhx[7]);
                break;

            case 33:
            case 34:
            case 35:
            case 36:
            case 37:
            case 38:
            case 39:
            case 40:
            case 41:
            case 42:
            case 43:
            case 44:
            case 45:
            case 46:
            case 47:
            case 48:
            case 49:
            case 50:
                /* unassigned */
                break;

            case 51:
                /* unknown */
                break;

            case 17:
            case 55:
                /* for some inscrutable reason page 17 is sent
                 * as page 55, IS-GPS-200E Table 20-V */
                sv = -1;
                /*
                 * "The requisite 176 bits shall occupy bits 9 through 24
                 * of word TWO, the 24 MSBs of words THREE through EIGHT,
                 * plus the 16 MSBs of word NINE." (word numbers changed
                 * to account for zero-indexing)
                 * Since we've already stripped the low six parity bits,
                 * and shifted the data to a byte boundary, we can just
                 * copy it out. */

                i = 0;
                subp->sub4_17.str[i++] = (words[2] >> 8) & 0xff;
                subp->sub4_17.str[i++] = (words[2]) & 0xff;

                subp->sub4_17.str[i++] = (words[3] >> 16) & 0xff;
                subp->sub4_17.str[i++] = (words[3] >> 8) & 0xff;
                subp->sub4_17.str[i++] = (words[3]) & 0xff;

                subp->sub4_17.str[i++] = (words[4] >> 16) & 0xff;
                subp->sub4_17.str[i++] = (words[4] >> 8) & 0xff;
                subp->sub4_17.str[i++] = (words[4]) & 0xff;

                subp->sub4_17.str[i++] = (words[5] >> 16) & 0xff;
                subp->sub4_17.str[i++] = (words[5] >> 8) & 0xff;
                subp->sub4_17.str[i++] = (words[5]) & 0xff;

                subp->sub4_17.str[i++] = (words[6] >> 16) & 0xff;
                subp->sub4_17.str[i++] = (words[6] >> 8) & 0xff;
                subp->sub4_17.str[i++] = (words[6]) & 0xff;

                subp->sub4_17.str[i++] = (words[7] >> 16) & 0xff;
                subp->sub4_17.str[i++] = (words[7] >> 8) & 0xff;
                subp->sub4_17.str[i++] = (words[7]) & 0xff;

                subp->sub4_17.str[i++] = (words[8] >> 16) & 0xff;
                subp->sub4_17.str[i++] = (words[8] >> 8) & 0xff;
                subp->sub4_17.str[i++] = (words[8]) & 0xff;

                subp->sub4_17.str[i++] = (words[9] >> 16) & 0xff;
                subp->sub4_17.str[i++] = (words[9] >> 8) & 0xff;
                subp->sub4_17.str[i] = '\0';
                GPSD_LOG(LOG_PROG, &session->context->errout,
                         "50B: SF:4-17 system message: %.24s\n",
                         subp->sub4_17.str);
                break;
            case 18:
            case 56:
                /* for some inscrutable reason page 18 is sent
                 * as page 56, IS-GPS-200E Table 20-V */
                /* ionospheric and UTC data */

                sv = -1;
                /* current leap seconds */
                subp->sub4_18.alpha0 = (int8_t)((words[2] >> 8) & 0x0000FF);
                subp->sub4_18.d_alpha0 = pow(2.0, -30) *
                                             (int)subp->sub4_18.alpha0;
                subp->sub4_18.alpha1 = (int8_t)((words[2] >> 0) & 0x0000FF);
                subp->sub4_18.d_alpha1 = pow(2.0, -27) * 
                                            (int)subp->sub4_18.alpha1;
                subp->sub4_18.alpha2 = (int8_t)((words[3] >> 16) & 0x0000FF);
                subp->sub4_18.d_alpha2 = pow(2.0, -24) * 
                                            (int)subp->sub4_18.alpha2;
                subp->sub4_18.alpha3 = (int8_t)((words[3] >>  8) & 0x0000FF);
                subp->sub4_18.d_alpha3 = pow(2.0, -24) * 
                                            (int)subp->sub4_18.alpha3;

                subp->sub4_18.beta0  = (int8_t)((words[3] >>  0) & 0x0000FF);
                subp->sub4_18.d_beta0 = pow(2.0, 11) * (int)subp->sub4_18.beta0;
                subp->sub4_18.beta1  = (int8_t)((words[4] >> 16) & 0x0000FF);
                subp->sub4_18.d_beta1 = pow(2.0, 14) * (int)subp->sub4_18.beta1;
                subp->sub4_18.beta2  = (int8_t)((words[4] >>  8) & 0x0000FF);
                subp->sub4_18.d_beta2 = pow(2.0, 16) * (int)subp->sub4_18.beta2;
                subp->sub4_18.beta3  = (int8_t)((words[4] >>  0) & 0x0000FF);
                subp->sub4_18.d_beta3 = pow(2.0, 16) * (int)subp->sub4_18.beta3;

                subp->sub4_18.A1     = (int32_t)((words[5] >>  0) & 0xFFFFFF);
                subp->sub4_18.A1     = uint2int(subp->sub4_18.A1, 24);
                subp->sub4_18.d_A1   = pow(2.0,-50) * subp->sub4_18.A1;
                subp->sub4_18.A0     = (int32_t)((words[6] >>  0) & 0xFFFFFF);
                subp->sub4_18.A0   <<= 8;
                subp->sub4_18.A0    |= ((words[7] >> 16) & 0x0000FF);
                subp->sub4_18.d_A0   = pow(2.0,-30) * subp->sub4_18.A0;

                /* careful WN is 10 bits, but WNt is 8 bits! */
                /* WNt (Week Number of LSF) */
                subp->sub4_18.tot    = ((words[7] >> 8) & 0x0000FF);
                subp->sub4_18.t_tot  = 2e12 * subp->sub4_18.tot;
                subp->sub4_18.WNt    = ((words[7] >> 0) & 0x0000FF);
                subp->sub4_18.leap  = (int8_t)((words[8] >> 16) & 0x0000FF);
                subp->sub4_18.WNlsf  = ((words[8] >>  8) & 0x0000FF);

                /* DN (Day Number of LSF) */
                subp->sub4_18.DN = (words[8] & 0x0000FF);
                /* leap second future */
                subp->sub4_18.lsf = (int8_t)((words[9] >> 16) & 0x0000FF);

                GPSD_LOG(LOG_PROG, &session->context->errout,
                         "50B: SF:4-18 a0:%.5g a1:%.5g a2:%.5g a3:%.5g "
                         "b0:%.5g b1:%.5g b2:%.5g b3:%.5g "
                         "A1:%.11e A0:%.11e tot:%lld WNt:%u "
                         "ls: %d WNlsf:%u DN:%u, lsf:%d\n",
                         subp->sub4_18.d_alpha0, subp->sub4_18.d_alpha1,
                         subp->sub4_18.d_alpha2, subp->sub4_18.d_alpha3,
                         subp->sub4_18.d_beta0, subp->sub4_18.d_beta1,
                         subp->sub4_18.d_beta2, subp->sub4_18.d_beta3,
                         subp->sub4_18.d_A1, subp->sub4_18.d_A0,
                         (long long)subp->sub4_18.t_tot, subp->sub4_18.WNt,
                         subp->sub4_18.leap, subp->sub4_18.WNlsf,
                         subp->sub4_18.DN, subp->sub4_18.lsf);

                /* notify the leap seconds correction in the end
                 * of current day */
                /* IS-GPS-200 Revision E, paragraph 20.3.3.5.2.4 */
                /* FIXME: only allow LEAPs in June and December */
                // only need to check whole seconds
                if (((session->context->gps_week % 256) ==
                     (unsigned short)subp->sub4_18.WNlsf) &&
                    (((subp->sub4_18.DN - 1) * SECS_PER_DAY) <
                     session->context->gps_tow.tv_sec) &&
                    ((subp->sub4_18.DN * SECS_PER_DAY) >
                     session->context->gps_tow.tv_sec)) {

                   if (subp->sub4_18.leap < subp->sub4_18.lsf) {
                        session->context->leap_notify = LEAP_ADDSECOND;
                   } else if (subp->sub4_18.leap > subp->sub4_18.lsf) {
                        session->context->leap_notify = LEAP_DELSECOND;
                   } else {
                        session->context->leap_notify = LEAP_NOWARNING;
                   }
                } else {
                   session->context->leap_notify = LEAP_NOWARNING;
                }

                session->context->leap_seconds = (int)subp->sub4_18.leap;
                session->context->valid |= LEAP_SECOND_VALID;
                break;
            default:
                ;                       /* no op */
            }
            if ( -1 < sv ) {
                subp->is_almanac = 1;
                subframe_almanac(&session->context->errout,
                                 subp->tSVID, words, subp->subframe_num,
                                 (uint8_t)sv, subp->data_id,
                                 &subp->sub4.almanac);
            } else if ( -2 == sv ) {
                /* unknown or secret page */
                GPSD_LOG(LOG_PROG, &session->context->errout,
                         "50B: SF:4-%d data_id %d\n",
                         subp->pageid, subp->data_id);
                return 0;
            }
            /* else, already handled */
        }
        break;
    case 5:
        /* Pages 0, dummy almanac for dummy SV 0
         * Pages 1 through 24: almanac data for SV 1 through 24
         * Page 25: SV health data for SV 1 through 24, the almanac
         * reference time, the almanac reference week number.
         */
        if ( 25 > subp->pageid ) {
            subp->is_almanac = 1;
            subframe_almanac(&session->context->errout,
                             subp->tSVID, words, subp->subframe_num,
                             subp->pageid, subp->data_id, &subp->sub5.almanac);
        } else if ( 51 == subp->pageid ) {
            /* for some inscrutable reason page 25 is sent as page 51
             * IS-GPS-200E Table 20-V */

            subp->sub5_25.toa   = ((words[2] >> 8) & 0x0000FF);
            subp->sub5_25.l_toa <<= 12;
            subp->sub5_25.WNa   = ( words[2] & 0x0000FF);
            subp->sub5_25.sv[1] = ((words[2] >> 18) & 0x00003F);
            subp->sub5_25.sv[2] = ((words[2] >> 12) & 0x00003F);
            subp->sub5_25.sv[3] = ((words[2] >>  6) & 0x00003F);
            subp->sub5_25.sv[4] = ((words[2] >>  0) & 0x00003F);
            subp->sub5_25.sv[5] = ((words[3] >> 18) & 0x00003F);
            subp->sub5_25.sv[6] = ((words[3] >> 12) & 0x00003F);
            subp->sub5_25.sv[7] = ((words[3] >>  6) & 0x00003F);
            subp->sub5_25.sv[8] = ((words[3] >>  0) & 0x00003F);
            subp->sub5_25.sv[9] = ((words[4] >> 18) & 0x00003F);
            subp->sub5_25.sv[10] = ((words[4] >> 12) & 0x00003F);
            subp->sub5_25.sv[11] = ((words[4] >>  6) & 0x00003F);
            subp->sub5_25.sv[12] = ((words[4] >>  0) & 0x00003F);
            subp->sub5_25.sv[13] = ((words[5] >> 18) & 0x00003F);
            subp->sub5_25.sv[14] = ((words[5] >> 12) & 0x00003F);
            subp->sub5_25.sv[15] = ((words[5] >>  6) & 0x00003F);
            subp->sub5_25.sv[16] = ((words[5] >>  0) & 0x00003F);
            subp->sub5_25.sv[17] = ((words[6] >> 18) & 0x00003F);
            subp->sub5_25.sv[18] = ((words[6] >> 12) & 0x00003F);
            subp->sub5_25.sv[19] = ((words[6] >>  6) & 0x00003F);
            subp->sub5_25.sv[20] = ((words[6] >>  0) & 0x00003F);
            subp->sub5_25.sv[21] = ((words[7] >> 18) & 0x00003F);
            subp->sub5_25.sv[22] = ((words[7] >> 12) & 0x00003F);
            subp->sub5_25.sv[23] = ((words[7] >>  6) & 0x00003F);
            subp->sub5_25.sv[24] = ((words[7] >>  0) & 0x00003F);
            GPSD_LOG(LOG_PROG, &session->context->errout,
                     "50B: SF:5-25 SV:%2u ID:%u toa:%lu WNa:%u "
                     "SV1:%u SV2:%u SV3:%u SV4:%u "
                     "SV5:%u SV6:%u SV7:%u SV8:%u "
                     "SV9:%u SV10:%u SV11:%u SV12:%u "
                     "SV13:%u SV14:%u SV15:%u SV16:%u "
                     "SV17:%u SV18:%u SV19:%u SV20:%u "
                     "SV21:%u SV22:%u SV23:%u SV24:%u\n",
                     subp->tSVID, subp->data_id,
                     subp->sub5_25.l_toa, subp->sub5_25.WNa,
                     subp->sub5_25.sv[1], subp->sub5_25.sv[2],
                     subp->sub5_25.sv[3], subp->sub5_25.sv[4],
                     subp->sub5_25.sv[5], subp->sub5_25.sv[6],
                     subp->sub5_25.sv[7], subp->sub5_25.sv[8],
                     subp->sub5_25.sv[9], subp->sub5_25.sv[10],
                     subp->sub5_25.sv[11], subp->sub5_25.sv[12],
                     subp->sub5_25.sv[13], subp->sub5_25.sv[14],
                     subp->sub5_25.sv[15], subp->sub5_25.sv[16],
                     subp->sub5_25.sv[17], subp->sub5_25.sv[18],
                     subp->sub5_25.sv[19], subp->sub5_25.sv[20],
                     subp->sub5_25.sv[21], subp->sub5_25.sv[22],
                     subp->sub5_25.sv[23], subp->sub5_25.sv[24]);
        } else {
            /* unknown page */
            GPSD_LOG(LOG_PROG, &session->context->errout,
                     "50B: SF:5-%d data_id %d unknown page\n",
                     subp->pageid, subp->data_id);
            return 0;
        }
        break;
    default:
        /* unknown/illegal subframe */
        return 0;
    }
    return SUBFRAME_SET;
}

// vim: set expandtab shiftwidth=4