summaryrefslogtreecommitdiffstats
path: root/gps.c
diff options
context:
space:
mode:
Diffstat (limited to 'gps.c')
-rw-r--r--gps.c126
1 files changed, 126 insertions, 0 deletions
diff --git a/gps.c b/gps.c
new file mode 100644
index 0000000..c235748
--- /dev/null
+++ b/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;
+}
+