verify that loaded almanac is valid (within a certain week number range)

Invalidate almanac in memory if invalid for a particular PRN

src/manage.c

@@ -12,6 +12,7 @@
 
 #include <math.h>
 #include <string.h>
+#include <stdlib.h>
 
 #include <ch.h>
 
@@ -88,7 +89,8 @@ static void almanac_callback(u16 sender_id, u8 len, u8 msg[], void* context)
 
   almanac_t *new_almanac = (almanac_t*)msg;
 
-  log_info("Received alamanc for PRN %02d\n", new_almanac->prn);
+  log_info("Received alamanc for PRN %02d with week %03d\n", new_almanac->prn,
+           new_almanac->week);
   memcpy(&almanac[new_almanac->prn-1], new_almanac, sizeof(almanac_t));
 
   int fd = cfs_open("almanac", CFS_WRITE);
@@ -129,26 +131,36 @@ void manage_acq_setup()
     acq_prn_param[prn].dopp_hint_low = ACQ_FULL_CF_MIN;
     acq_prn_param[prn].dopp_hint_high = ACQ_FULL_CF_MAX;
   }
-
   int fd = cfs_open("almanac", CFS_READ);
   if (fd != -1) {
     cfs_read(fd, almanac, 32*sizeof(almanac_t));
-    log_info("Loaded almanac from flash\n");
+    u16 wn = 0;
+    for (u8 prn=0; prn<32; prn++){
+      /* get the week number for the first valid satellite to report */
+      if(almanac[prn].valid) {
+        wn=almanac[prn].week;
+        break;
+        }
+    }
+    /* we only print that the almanac was loaded if there was a valid sat within */
+    if (wn != 0) {
+    log_info("Loaded almanac from flash with week number %03d\n", wn);
+    }
     cfs_close(fd);
-  } else {
+  }
+  else {
     log_info("No almanac file present in flash, create an empty one\n");
     cfs_coffee_reserve("almanac", 32*sizeof(almanac_t));
     cfs_coffee_configure_log("almanac", 256, sizeof(almanac_t));
-
+    /* set all satellites to invalid when creating a placeholder */
     for (u8 prn=0; prn<32; prn++) {
-      almanac[prn].valid = 0;
+    almanac[prn].valid = 0;
     }
   }
-
-  sbp_register_cbk(
-    SBP_MSG_ALMANAC,
-    &almanac_callback,
-    &almanac_callback_node
+    sbp_register_cbk(
+      SBP_MSG_ALMANAC,
+      &almanac_callback,
+      &almanac_callback_node
   );
 
   chThdCreateStatic(
@@ -171,8 +183,16 @@ static void manage_calc_almanac_scores(void)
       /* No almanac or position/time information, give it the benefit of the
        * doubt. */
       acq_prn_param[prn].score[ACQ_HINT_ALMANAC] = 0;
+    } else if (almanac[prn].valid && time_quality > TIME_COARSE &&
+              (abs(almanac[prn].week - t.wn%1024) > MAX_ALM_WEEK_DIFF)) {
+      /* If our almanac is out of date with respect to a time estimate of
+       * coarse or better, we invalidate it */
+      log_info("Almanac for prn %i and week %i is out of date, invalidating it.",
+               prn, almanac[prn].week);
+      almanac[prn].valid = 0;
     } else {
-      calc_sat_az_el_almanac(&almanac[prn], t.tow, t.wn-1024, position_solution.pos_ecef, &az, &el);
+      calc_sat_az_el_almanac(&almanac[prn], t.tow, t.wn-1024,
+                             position_solution.pos_ecef, &az, &el);
       float dopp = -calc_sat_doppler_almanac(&almanac[prn], t.tow, t.wn,
                                              position_solution.pos_ecef);
       acq_prn_param[prn].score[ACQ_HINT_ALMANAC] =

src/manage.h

@@ -38,6 +38,7 @@
 #define MANAGE_TRACK_THREAD_PRIORITY (NORMALPRIO-2)
 #define MANAGE_TRACK_THREAD_STACK    3000
 
+#define MAX_ALM_WEEK_DIFF 6
 /** \} */
 
 void manage_acq_setup(void);