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Diffstat (limited to 'rrlp-ephemeris/gps.c')
-rw-r--r-- | rrlp-ephemeris/gps.c | 126 |
1 files changed, 126 insertions, 0 deletions
diff --git a/rrlp-ephemeris/gps.c b/rrlp-ephemeris/gps.c new file mode 100644 index 000000000..c23574840 --- /dev/null +++ b/rrlp-ephemeris/gps.c @@ -0,0 +1,126 @@ +/* + * gps.c + * + * A few utility functions to deal with low level GPS data + * + * + * Copyright (C) 2009 Sylvain Munaut <tnt@246tNt.com> + * + * This program is free software: you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation, either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program. If not, see <http://www.gnu.org/licenses/>. + */ + +#include "gps.h" + + +#define GET_FIELD_U(w, nb, pos) (((w) >> (pos)) & ((1<<(nb))-1)) +#define GET_FIELD_S(w, nb, pos) (((int)((w) << (32-(nb)-(pos)))) >> (32-(nb))) + +/* + * Unpacks GPS Subframe 1,2,3 payloads (3 * 8 words) + * + * Note: eph->sv_id is not filled here since not present in those subframes + * + * (no parity bit checking is done, only the lower 24 bits of each word + * are used) + */ +int +gps_unpack_sf123(uint32_t *sf, struct gps_ephemeris_sv *eph) +{ + uint32_t *sf1 = &sf[0]; + uint32_t *sf2 = &sf[8]; + uint32_t *sf3 = &sf[16]; + + int iode1, iode2; + + eph->week_no = GET_FIELD_U(sf1[0], 10, 14); + eph->code_on_l2 = GET_FIELD_U(sf1[0], 2, 12); + eph->sv_ura = GET_FIELD_U(sf1[0], 4, 8); + eph->sv_health = GET_FIELD_U(sf1[0], 6, 2); + eph->l2_p_flag = GET_FIELD_U(sf1[1], 1, 23); + eph->t_gd = GET_FIELD_S(sf1[4], 8, 0); + eph->iodc = (GET_FIELD_U(sf1[0], 2, 0) << 8) | \ + GET_FIELD_U(sf1[5], 8, 16); + eph->t_oc = GET_FIELD_U(sf1[5], 16, 0); + eph->a_f2 = GET_FIELD_S(sf1[6], 8, 16); + eph->a_f1 = GET_FIELD_S(sf1[6], 16, 0); + eph->a_f0 = GET_FIELD_S(sf1[7], 22, 2); + + iode1 = GET_FIELD_U(sf2[0], 8, 16); + eph->c_rs = GET_FIELD_S(sf2[0], 16, 0); + eph->delta_n = GET_FIELD_S(sf2[1], 16, 8); + eph->m_0 = (GET_FIELD_S(sf2[1], 8, 0) << 24) | \ + GET_FIELD_U(sf2[2], 24, 0); + eph->c_uc = GET_FIELD_S(sf2[3], 16, 8); + eph->e = (GET_FIELD_U(sf2[3], 8, 0) << 24) | \ + GET_FIELD_U(sf2[4], 24, 0); + eph->c_us = GET_FIELD_S(sf2[5], 16, 8); + eph->a_powhalf = (GET_FIELD_U(sf2[5], 8, 0) << 24) | \ + GET_FIELD_U(sf2[6], 24, 0); + eph->t_oe = GET_FIELD_U(sf2[7], 16, 8); + eph->fit_flag = GET_FIELD_U(sf2[7], 1, 7); + + eph->c_ic = GET_FIELD_S(sf3[0], 16, 8); + eph->omega_0 = (GET_FIELD_S(sf3[0], 8, 0) << 24) | \ + GET_FIELD_U(sf3[1], 24, 0); + eph->c_is = GET_FIELD_S(sf3[2], 16, 8); + eph->i_0 = (GET_FIELD_S(sf3[2], 8, 0) << 24) | \ + GET_FIELD_U(sf3[3], 24, 0); + eph->c_rc = GET_FIELD_S(sf3[4], 16, 8); + eph->w = (GET_FIELD_S(sf3[4], 8, 0) << 24) | \ + GET_FIELD_U(sf3[5], 24, 0); + eph->omega_dot = GET_FIELD_S(sf3[6], 24, 0); + iode2 = GET_FIELD_U(sf3[7], 8, 16); + eph->idot = GET_FIELD_S(sf3[7], 14, 2); + + eph->_rsvd1 = GET_FIELD_U(sf1[1], 23, 0); + eph->_rsvd2 = GET_FIELD_U(sf1[2], 24, 0); + eph->_rsvd3 = GET_FIELD_U(sf1[3], 24, 0); + eph->_rsvd4 = GET_FIELD_U(sf1[4], 16, 8); + eph->aodo = GET_FIELD_U(sf2[7], 5, 2); + + /* Check & cross-validate iodc[7:0], iode1, iode2 */ + if ((iode1 != iode2) || (iode1 != (eph->iodc & 0xff))) + return -1; + + return 0; +} + + +/* + * Unpacks GPS Subframe 4 or 5 Almanac pages payload (8 words) + * + * (no parity bit checking is done, only the lower 24 bits of each word + * are used) + */ +int +gps_unpack_sf45_almanac(uint32_t *sf, struct gps_almanac_sv *alm) +{ + alm->sv_id = GET_FIELD_U(sf[0], 6, 16); + + alm->e = GET_FIELD_U(sf[0], 16, 0); + alm->t_oa = GET_FIELD_U(sf[1], 8, 16); + alm->ksii = GET_FIELD_S(sf[1], 16, 0); + alm->omega_dot = GET_FIELD_S(sf[2], 16, 8); + alm->sv_health = GET_FIELD_U(sf[2], 8, 0); + alm->a_powhalf = GET_FIELD_U(sf[3], 24, 0); + alm->omega_0 = GET_FIELD_S(sf[4], 24, 0); + alm->w = GET_FIELD_S(sf[5], 24, 0); + alm->m_0 = GET_FIELD_S(sf[6], 24, 0); + alm->a_f0 = (GET_FIELD_S(sf[7], 8, 16) << 3) | \ + GET_FIELD_U(sf[7], 3, 2); + alm->a_f1 = GET_FIELD_S(sf[7], 11, 5); + + return 0; +} + |