Import code to generate RRLP ephemeris data from u-blox GPS receiver
taken from http://www.246tnt.com/files/rrlp-20091101.tar.bz2
diff --git a/rrlp-ephemeris/ubx.c b/rrlp-ephemeris/ubx.c
new file mode 100644
index 0000000..83dd1f0
--- /dev/null
+++ b/rrlp-ephemeris/ubx.c
@@ -0,0 +1,81 @@
+/*
+ * ubx.c
+ *
+ * Implementation of generic UBX helpers
+ *
+ *
+ * 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 <stdio.h>
+#include <stdint.h>
+
+#include "ubx.h"
+
+
+static void
+ubx_checksum(uint8_t *data, int len, uint8_t *cksum)
+{
+ int i;
+ uint8_t ck0 = 0, ck1 = 0;
+ for (i=0; i<len; i++) {
+ ck0 += data[i];
+ ck1 += ck0;
+ }
+ cksum[0] = ck0;
+ cksum[1] = ck1;
+}
+
+
+static ubx_msg_handler_t
+ubx_find_handler(struct ubx_dispatch_entry *dt, uint8_t msg_class, uint8_t msg_id)
+{
+ while (dt->handler) {
+ if ((dt->msg_class == msg_class) && (dt->msg_id == msg_id))
+ return dt->handler;
+ dt++;
+ }
+ return NULL;
+}
+
+
+int
+ubx_msg_dispatch(struct ubx_dispatch_entry *dt,
+ void *msg, int len, void *userdata)
+{
+ struct ubx_hdr *hdr = msg;
+ uint8_t cksum[2], *cksum_ptr;
+ ubx_msg_handler_t h;
+
+ if ((hdr->sync[0] != UBX_SYNC0) || (hdr->sync[1] != UBX_SYNC1)) {
+ fprintf(stderr, "[!] Invalid sync bytes\n");
+ return -1;
+ }
+
+ ubx_checksum(msg + 2, sizeof(struct ubx_hdr) + hdr->payload_len - 2, cksum);
+ cksum_ptr = msg + (sizeof(struct ubx_hdr) + hdr->payload_len);
+ if ((cksum_ptr[0] != cksum[0]) || (cksum_ptr[1] != cksum[1])) {
+ fprintf(stderr, "[!] Invalid checksum\n");
+ return -1;
+ }
+
+ h = ubx_find_handler(dt, hdr->msg_class, hdr->msg_id);
+ if (h)
+ h(hdr, msg + sizeof(struct ubx_hdr), hdr->payload_len, userdata);
+
+ return sizeof(struct ubx_hdr) + hdr->payload_len + 2;
+}
+