fix problem with cache

Author: error414

src/main/terrain/terrain.c

@@ -92,6 +92,9 @@ static float getGeigHtAmslMeters(const gpsLocation_t *loc)
 
     // find the grid
     gridBlock_t *grid = &(findGridCache(&info)->gridBlock);
+    if(grid  == NULL){
+        return TERRAIN_STATUS_CACHE_FULL;
+    }
 
     // check we have all 4 required heights, it's check if grid is loaded from SD card
     if (!checkBitmap(grid, info.idx_x,   info.idx_y) || !checkBitmap(grid, info.idx_x, info.idx_y + 1) || !checkBitmap(grid, info.idx_x + 1, info.idx_y) || !checkBitmap(grid, info.idx_x + 1, info.idx_y + 1)) {

src/main/terrain/terrain.h

@@ -36,6 +36,7 @@
 #define TERRAIN_STATUS_WRONG_BITMAP (-3)
 #define TERRAIN_STATUS_NO_DATA (-4)
 #define TERRAIN_STATUS_NO_CARD (-5)
+#define TERRAIN_STATUS_CACHE_FULL (-6)
 
 // MAVLink sends 4x4 grids
 #define TERRAIN_GRID_MAVLINK_SIZE 4

src/main/terrain/terrain_utils.c

@@ -177,7 +177,7 @@ uint32_t eastBlocks(gridBlock_t *gridBlock)
  */
 gridCache_t* findGridCache(gridInfo_t *info)
 {
-    uint16_t oldest_i = 0;
+    int16_t oldest_i = -1;
 
     // see if we have that grid
     const timeMs_t nowMs = millis();
@@ -190,13 +190,17 @@ gridCache_t* findGridCache(gridInfo_t *info)
             cache[i].lastAccessMs = nowMs;
             return &cache[i];
         }
-        if (cache[i].lastAccessMs < cache[oldest_i].lastAccessMs) {
-            oldest_i = i;
+        if (cache[i].lastAccessMs < cache[oldest_i].lastAccessMs && cache[oldest_i].state != GRID_CACHE_DISKWAIT) {
+            oldest_i = (int16_t)i;
         }
     }
 
     // Not found. Use the oldest grid and make it this grid,
     // initially unpopulated
+    if(oldest_i < 0){
+        return NULL;
+    }
+
     gridCache_t *gridCache = &cache[oldest_i];
     memset(gridCache, 0, sizeof(gridCache_t));