From 5cf2c2740ef3134bb9c4136405ee3bc0b88dedc8 Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <andrew@tridgell.net>
Date: Sun, 13 Nov 2022 10:27:37 +1100
Subject: [PATCH] AP_Terrain: added parameter for terrain cache size

---
 libraries/AP_Terrain/AP_Terrain.cpp | 13 ++++++++++---
 libraries/AP_Terrain/AP_Terrain.h   |  3 +++
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/libraries/AP_Terrain/AP_Terrain.cpp b/libraries/AP_Terrain/AP_Terrain.cpp
index d2aab8bf1d8ab..48966bfbe161c 100644
--- a/libraries/AP_Terrain/AP_Terrain.cpp
+++ b/libraries/AP_Terrain/AP_Terrain.cpp
@@ -77,7 +77,14 @@ const AP_Param::GroupInfo AP_Terrain::var_info[] = {
     // @Range: 0 50
     // @User: Advanced
     AP_GROUPINFO("OFS_MAX",  4, AP_Terrain, offset_max, 30),
-    
+
+    // @Param: CACHE_SZ
+    // @DisplayName: Terrain cache size
+    // @Description: The number of 32x28 cache blocks to keep in memory. Each block uses about 1800 bytes of memory
+    // @Range: 0 128
+    // @User: Advanced
+    AP_GROUPINFO("CACHE_SZ",  5, AP_Terrain, config_cache_size, TERRAIN_GRID_BLOCK_CACHE_SIZE),
+
     AP_GROUPEND
 };
 
@@ -488,13 +495,13 @@ bool AP_Terrain::allocate(void)
     if (cache != nullptr) {
         return true;
     }
-    cache = (struct grid_cache *)calloc(TERRAIN_GRID_BLOCK_CACHE_SIZE, sizeof(cache[0]));
+    cache = (struct grid_cache *)calloc(config_cache_size, sizeof(cache[0]));
     if (cache == nullptr) {
         GCS_SEND_TEXT(MAV_SEVERITY_CRITICAL, "Terrain: Allocation failed");
         memory_alloc_failed = true;
         return false;
     }
-    cache_size = TERRAIN_GRID_BLOCK_CACHE_SIZE;
+    cache_size = config_cache_size;
     return true;
 }
 
diff --git a/libraries/AP_Terrain/AP_Terrain.h b/libraries/AP_Terrain/AP_Terrain.h
index 8a6be4579db06..7dfd2653d8475 100644
--- a/libraries/AP_Terrain/AP_Terrain.h
+++ b/libraries/AP_Terrain/AP_Terrain.h
@@ -51,7 +51,9 @@
 #define TERRAIN_GRID_BLOCK_SIZE_Y (TERRAIN_GRID_MAVLINK_SIZE*TERRAIN_GRID_BLOCK_MUL_Y)
 
 // number of grid_blocks in the LRU memory cache
+#ifndef TERRAIN_GRID_BLOCK_CACHE_SIZE
 #define TERRAIN_GRID_BLOCK_CACHE_SIZE 12
+#endif
 
 // format of grid on disk
 #define TERRAIN_GRID_FORMAT_VERSION 1
@@ -371,6 +373,7 @@ class AP_Terrain {
     AP_Int16 grid_spacing; // meters between grid points
     AP_Int16 options; // option bits
     AP_Float offset_max;
+    AP_Int16 config_cache_size;
 
     enum class Options {
         DisableDownload = (1U<<0),