Dynamic allocation for SDCARD_SORT_ALPHA

Marlin/Configuration_adv.h

@@ -463,6 +463,7 @@
    *  - SDSORT_USES_RAM provides faster sorting via a static directory buffer.
    *  - SDSORT_USES_STACK does the same, but uses a local stack-based buffer.
    *  - SDSORT_CACHE_NAMES will retain the sorted file listing in RAM. (Expensive!)
+   *  - SDSORT_DYNAMIC_RAM only uses RAM when the SD menu is visible. (Use with caution!)
    */
   //#define SDCARD_SORT_ALPHA
 
@@ -474,6 +475,7 @@
     #define SDSORT_USES_RAM    false  // Pre-allocate a static array for faster pre-sorting.
     #define SDSORT_USES_STACK  false  // Prefer the stack for pre-sorting to give back some SRAM. (Negated by next 2 options.)
     #define SDSORT_CACHE_NAMES false  // Keep sorted items in RAM longer for speedy performance. Most expensive option.
+    #define SDSORT_DYNAMIC_RAM false  // Use dynamic allocation (within SD menus). Least expensive option. Set SDSORT_LIMIT before use!
   #endif
 
   // Show a progress bar on HD44780 LCDs for SD printing

Marlin/SanityCheck.h

@@ -213,8 +213,12 @@
     #error "SDSORT_LIMIT must be 256 or smaller."
   #elif SDSORT_LIMIT < 10
     #error "SDSORT_LIMIT should be greater than 9 to be useful."
-  #elif DISABLED(SDSORT_USES_RAM) && ENABLED(SDSORT_CACHE_NAMES)
-    #error "SDSORT_CACHE_NAMES requires SDSORT_USES_RAM (which reads the directory into RAM)."
+  #elif DISABLED(SDSORT_USES_RAM)
+    #if ENABLED(SDSORT_DYNAMIC_RAM)
+      #error "SDSORT_DYNAMIC_RAM requires SDSORT_USES_RAM (which reads the directory into RAM)."
+    #elif ENABLED(SDSORT_CACHE_NAMES)
+      #error "SDSORT_CACHE_NAMES requires SDSORT_USES_RAM (which reads the directory into RAM)."
+    #endif
   #endif
 #endif
 

Marlin/cardreader.cpp

@@ -676,16 +676,30 @@ void CardReader::updir() {
       // If you use folders to organize, 20 may be enough
       if (fileCnt > SDSORT_LIMIT) fileCnt = SDSORT_LIMIT;
 
+      // Sort order is always needed. May be static or dynamic.
+      #if ENABLED(SDSORT_DYNAMIC_RAM)
+        sort_order = new uint8_t[fileCnt];
+      #endif
+
       // Use RAM to store the entire directory during pre-sort.
       // SDSORT_LIMIT should be set to prevent over-allocation.
       #if ENABLED(SDSORT_USES_RAM)
 
-        #if ENABLED(SDSORT_USES_STACK)
-          #if DISABLED(SDSORT_CACHE_NAMES)
-            char sortnames[fileCnt][LONG_FILENAME_LENGTH];
+        // If using dynamic ram for names, allocate on the heap.
+        #if ENABLED(SDSORT_CACHE_NAMES)
+          #if ENABLED(SDSORT_DYNAMIC_RAM)
+            sortshort = new char*[fileCnt];
+            sortnames = new char*[fileCnt];
           #endif
-          // Folder sorting needs 1 bit per entry for flags.
-          #if HAS_FOLDER_SORTING
+        #elif ENABLED(SDSORT_USES_STACK)
+          char sortnames[fileCnt][LONG_FILENAME_LENGTH];
+        #endif
+
+        // Folder sorting needs 1 bit per entry for flags.
+        #if HAS_FOLDER_SORTING
+          #if ENABLED(SDSORT_DYNAMIC_RAM)
+            isDir = new uint8_t[(fileCnt + 7) >> 3];
+          #elif ENABLED(SDSORT_USES_STACK)
             uint8_t isDir[(fileCnt + 7) >> 3];
           #endif
         #endif
@@ -707,9 +721,20 @@ void CardReader::updir() {
           // If using RAM then read all filenames now.
           #if ENABLED(SDSORT_USES_RAM)
             getfilename(i);
-            strcpy(sortnames[i], LONGEST_FILENAME);
-            #if ENABLED(SDSORT_CACHE_NAMES)
-              strcpy(sortshort[i], filename);
+            #if ENABLED(SDSORT_DYNAMIC_RAM)
+              // Use dynamic method to copy long filename
+              sortnames[i] = strdup(LONGEST_FILENAME);
+              #if ENABLED(SDSORT_CACHE_NAMES)
+                // When caching also store the short name, since
+                // we're replacing the getfilename() behavior.
+                sortshort[i] = strdup(filename);
+              #endif
+            #else
+              // Copy filenames into the static array
+              strcpy(sortnames[i], LONGEST_FILENAME);
+              #if ENABLED(SDSORT_CACHE_NAMES)
+                strcpy(sortshort[i], filename);
+              #endif
             #endif
             // char out[30];
             // sprintf_P(out, PSTR("---- %i %s %s"), i, filenameIsDir ? "D" : " ", sortnames[i]);
@@ -780,13 +805,30 @@ void CardReader::updir() {
           }
           if (!didSwap) break;
         }
+        // Using RAM but not keeping names around
+        #if ENABLED(SDSORT_USES_RAM) && DISABLED(SDSORT_CACHE_NAMES)
+          #if ENABLED(SDSORT_DYNAMIC_RAM)
+            for (uint16_t i = 0; i < fileCnt; ++i) free(sortnames[i]);
+            #if HAS_FOLDER_SORTING
+              free(isDir);
+            #endif
+          #endif
+        #endif
       }
       else {
         sort_order[0] = 0;
         #if ENABLED(SDSORT_USES_RAM) && ENABLED(SDSORT_CACHE_NAMES)
           getfilename(0);
-          strcpy(sortnames[0], LONGEST_FILENAME);
-          strcpy(sortshort[0], filename);
+          #if ENABLED(SDSORT_DYNAMIC_RAM)
+            sortnames = new char*[1];
+            sortnames[0] = strdup(LONGEST_FILENAME); // malloc
+            sortshort = new char*[1];
+            sortshort[0] = strdup(filename);         // malloc
+            isDir = new uint8_t[1];
+          #else
+            strcpy(sortnames[0], LONGEST_FILENAME);
+            strcpy(sortshort[0], filename);
+          #endif
           isDir[0] = filenameIsDir ? 0x01 : 0x00;
         #endif
       }
@@ -796,7 +838,20 @@ void CardReader::updir() {
   }
 
   void CardReader::flush_presort() {
-    sort_count = 0;
+    if (sort_count > 0) {
+      #if ENABLED(SDSORT_DYNAMIC_RAM)
+        delete sort_order;
+        #if ENABLED(SDSORT_CACHE_NAMES)
+          for (uint8_t i = 0; i < sort_count; ++i) {
+            free(sortshort[i]); // strdup
+            free(sortnames[i]); // strdup
+          }
+          delete sortshort;
+          delete sortnames;
+        #endif
+      #endif
+      sort_count = 0;
+    }
   }
 
 #endif // SDCARD_SORT_ALPHA

Marlin/cardreader.h

@@ -104,22 +104,35 @@ private:
       //bool sort_reverse;      // Flag to enable / disable reverse sorting
     #endif
 
-    uint8_t sort_order[SDSORT_LIMIT];
+    // By default the sort index is static
+    #if ENABLED(SDSORT_DYNAMIC_RAM)
+      uint8_t *sort_order;
+    #else
+      uint8_t sort_order[SDSORT_LIMIT];
+    #endif
 
     // Cache filenames to speed up SD menus.
     #if ENABLED(SDSORT_USES_RAM)
 
       // If using dynamic ram for names, allocate on the heap.
       #if ENABLED(SDSORT_CACHE_NAMES)
-        char sortshort[SDSORT_LIMIT][FILENAME_LENGTH];
-        char sortnames[SDSORT_LIMIT][FILENAME_LENGTH];
+        #if ENABLED(SDSORT_DYNAMIC_RAM)
+          char **sortshort, **sortnames;
+        #else
+          char sortshort[SDSORT_LIMIT][FILENAME_LENGTH];
+          char sortnames[SDSORT_LIMIT][FILENAME_LENGTH];
+        #endif
       #elif DISABLED(SDSORT_USES_STACK)
         char sortnames[SDSORT_LIMIT][FILENAME_LENGTH];
       #endif
 
       // Folder sorting uses an isDir array when caching items.
-      #if HAS_FOLDER_SORTING && (ENABLED(SDSORT_CACHE_NAMES) || DISABLED(SDSORT_USES_STACK))
-        uint8_t isDir[(SDSORT_LIMIT+7)>>3];
+      #if HAS_FOLDER_SORTING
+        #if ENABLED(SDSORT_DYNAMIC_RAM)
+          uint8_t *isDir;
+        #elif ENABLED(SDSORT_CACHE_NAMES) || DISABLED(SDSORT_USES_STACK)
+          uint8_t isDir[(SDSORT_LIMIT+7)>>3];
+        #endif
       #endif
 
     #endif // SDSORT_USES_RAM

Marlin/example_configurations/Cartesio/Configuration_adv.h

@@ -463,6 +463,7 @@
    *  - SDSORT_USES_RAM provides faster sorting via a static directory buffer.
    *  - SDSORT_USES_STACK does the same, but uses a local stack-based buffer.
    *  - SDSORT_CACHE_NAMES will retain the sorted file listing in RAM. (Expensive!)
+   *  - SDSORT_DYNAMIC_RAM only uses RAM when the SD menu is visible. (Use with caution!)
    */
   //#define SDCARD_SORT_ALPHA
 
@@ -474,6 +475,7 @@
     #define SDSORT_USES_RAM    false  // Pre-allocate a static array for faster pre-sorting.
     #define SDSORT_USES_STACK  false  // Prefer the stack for pre-sorting to give back some SRAM. (Negated by next 2 options.)
     #define SDSORT_CACHE_NAMES false  // Keep sorted items in RAM longer for speedy performance. Most expensive option.
+    #define SDSORT_DYNAMIC_RAM false  // Use dynamic allocation (within SD menus). Least expensive option. Set SDSORT_LIMIT before use!
   #endif
 
   // Show a progress bar on HD44780 LCDs for SD printing

Marlin/example_configurations/Felix/Configuration_adv.h

@@ -463,6 +463,7 @@
    *  - SDSORT_USES_RAM provides faster sorting via a static directory buffer.
    *  - SDSORT_USES_STACK does the same, but uses a local stack-based buffer.
    *  - SDSORT_CACHE_NAMES will retain the sorted file listing in RAM. (Expensive!)
+   *  - SDSORT_DYNAMIC_RAM only uses RAM when the SD menu is visible. (Use with caution!)
    */
   //#define SDCARD_SORT_ALPHA
 
@@ -474,6 +475,7 @@
     #define SDSORT_USES_RAM    false  // Pre-allocate a static array for faster pre-sorting.
     #define SDSORT_USES_STACK  false  // Prefer the stack for pre-sorting to give back some SRAM. (Negated by next 2 options.)
     #define SDSORT_CACHE_NAMES false  // Keep sorted items in RAM longer for speedy performance. Most expensive option.
+    #define SDSORT_DYNAMIC_RAM false  // Use dynamic allocation (within SD menus). Least expensive option. Set SDSORT_LIMIT before use!
   #endif
 
   // Show a progress bar on HD44780 LCDs for SD printing

Marlin/example_configurations/Hephestos/Configuration_adv.h

@@ -463,6 +463,7 @@
    *  - SDSORT_USES_RAM provides faster sorting via a static directory buffer.
    *  - SDSORT_USES_STACK does the same, but uses a local stack-based buffer.
    *  - SDSORT_CACHE_NAMES will retain the sorted file listing in RAM. (Expensive!)
+   *  - SDSORT_DYNAMIC_RAM only uses RAM when the SD menu is visible. (Use with caution!)
    */
   //#define SDCARD_SORT_ALPHA
 
@@ -474,6 +475,7 @@
     #define SDSORT_USES_RAM    false  // Pre-allocate a static array for faster pre-sorting.
     #define SDSORT_USES_STACK  false  // Prefer the stack for pre-sorting to give back some SRAM. (Negated by next 2 options.)
     #define SDSORT_CACHE_NAMES false  // Keep sorted items in RAM longer for speedy performance. Most expensive option.
+    #define SDSORT_DYNAMIC_RAM false  // Use dynamic allocation (within SD menus). Least expensive option. Set SDSORT_LIMIT before use!
   #endif
 
   // Show a progress bar on HD44780 LCDs for SD printing

Marlin/example_configurations/Hephestos_2/Configuration_adv.h

@@ -463,6 +463,7 @@
    *  - SDSORT_USES_RAM provides faster sorting via a static directory buffer.
    *  - SDSORT_USES_STACK does the same, but uses a local stack-based buffer.
    *  - SDSORT_CACHE_NAMES will retain the sorted file listing in RAM. (Expensive!)
+   *  - SDSORT_DYNAMIC_RAM only uses RAM when the SD menu is visible. (Use with caution!)
    */
   //#define SDCARD_SORT_ALPHA
 
@@ -474,6 +475,7 @@
     #define SDSORT_USES_RAM    false  // Pre-allocate a static array for faster pre-sorting.
     #define SDSORT_USES_STACK  false  // Prefer the stack for pre-sorting to give back some SRAM. (Negated by next 2 options.)
     #define SDSORT_CACHE_NAMES false  // Keep sorted items in RAM longer for speedy performance. Most expensive option.
+    #define SDSORT_DYNAMIC_RAM false  // Use dynamic allocation (within SD menus). Least expensive option. Set SDSORT_LIMIT before use!
   #endif
 
   // Show a progress bar on HD44780 LCDs for SD printing

Marlin/example_configurations/K8200/Configuration_adv.h

@@ -476,6 +476,7 @@
    *  - SDSORT_USES_RAM provides faster sorting via a static directory buffer.
    *  - SDSORT_USES_STACK does the same, but uses a local stack-based buffer.
    *  - SDSORT_CACHE_NAMES will retain the sorted file listing in RAM. (Expensive!)
+   *  - SDSORT_DYNAMIC_RAM only uses RAM when the SD menu is visible. (Use with caution!)
    */
   //#define SDCARD_SORT_ALPHA
 
@@ -487,6 +488,7 @@
     #define SDSORT_USES_RAM    false  // Pre-allocate a static array for faster pre-sorting.
     #define SDSORT_USES_STACK  false  // Prefer the stack for pre-sorting to give back some SRAM. (Negated by next 2 options.)
     #define SDSORT_CACHE_NAMES false  // Keep sorted items in RAM longer for speedy performance. Most expensive option.
+    #define SDSORT_DYNAMIC_RAM false  // Use dynamic allocation (within SD menus). Least expensive option. Set SDSORT_LIMIT before use!
   #endif
 
   // Show a progress bar on HD44780 LCDs for SD printing

Marlin/example_configurations/K8400/Configuration_adv.h

@@ -463,6 +463,7 @@
    *  - SDSORT_USES_RAM provides faster sorting via a static directory buffer.
    *  - SDSORT_USES_STACK does the same, but uses a local stack-based buffer.
    *  - SDSORT_CACHE_NAMES will retain the sorted file listing in RAM. (Expensive!)
+   *  - SDSORT_DYNAMIC_RAM only uses RAM when the SD menu is visible. (Use with caution!)
    */
   //#define SDCARD_SORT_ALPHA
 
@@ -474,6 +475,7 @@
     #define SDSORT_USES_RAM    false  // Pre-allocate a static array for faster pre-sorting.
     #define SDSORT_USES_STACK  false  // Prefer the stack for pre-sorting to give back some SRAM. (Negated by next 2 options.)
     #define SDSORT_CACHE_NAMES false  // Keep sorted items in RAM longer for speedy performance. Most expensive option.
+    #define SDSORT_DYNAMIC_RAM false  // Use dynamic allocation (within SD menus). Least expensive option. Set SDSORT_LIMIT before use!
   #endif
 
   // Show a progress bar on HD44780 LCDs for SD printing

Marlin/example_configurations/RigidBot/Configuration_adv.h

@@ -463,6 +463,7 @@
    *  - SDSORT_USES_RAM provides faster sorting via a static directory buffer.
    *  - SDSORT_USES_STACK does the same, but uses a local stack-based buffer.
    *  - SDSORT_CACHE_NAMES will retain the sorted file listing in RAM. (Expensive!)
+   *  - SDSORT_DYNAMIC_RAM only uses RAM when the SD menu is visible. (Use with caution!)
    */
   //#define SDCARD_SORT_ALPHA
 
@@ -474,6 +475,7 @@
     #define SDSORT_USES_RAM    false  // Pre-allocate a static array for faster pre-sorting.
     #define SDSORT_USES_STACK  false  // Prefer the stack for pre-sorting to give back some SRAM. (Negated by next 2 options.)
     #define SDSORT_CACHE_NAMES false  // Keep sorted items in RAM longer for speedy performance. Most expensive option.
+    #define SDSORT_DYNAMIC_RAM false  // Use dynamic allocation (within SD menus). Least expensive option. Set SDSORT_LIMIT before use!
   #endif
 
   // Show a progress bar on HD44780 LCDs for SD printing

Marlin/example_configurations/SCARA/Configuration_adv.h

@@ -463,6 +463,7 @@
    *  - SDSORT_USES_RAM provides faster sorting via a static directory buffer.
    *  - SDSORT_USES_STACK does the same, but uses a local stack-based buffer.
    *  - SDSORT_CACHE_NAMES will retain the sorted file listing in RAM. (Expensive!)
+   *  - SDSORT_DYNAMIC_RAM only uses RAM when the SD menu is visible. (Use with caution!)
    */
   //#define SDCARD_SORT_ALPHA
 
@@ -474,6 +475,7 @@
     #define SDSORT_USES_RAM    false  // Pre-allocate a static array for faster pre-sorting.
     #define SDSORT_USES_STACK  false  // Prefer the stack for pre-sorting to give back some SRAM. (Negated by next 2 options.)
     #define SDSORT_CACHE_NAMES false  // Keep sorted items in RAM longer for speedy performance. Most expensive option.
+    #define SDSORT_DYNAMIC_RAM false  // Use dynamic allocation (within SD menus). Least expensive option. Set SDSORT_LIMIT before use!
   #endif
 
   // Show a progress bar on HD44780 LCDs for SD printing

Marlin/example_configurations/TAZ4/Configuration_adv.h

@@ -471,6 +471,7 @@
    *  - SDSORT_USES_RAM provides faster sorting via a static directory buffer.
    *  - SDSORT_USES_STACK does the same, but uses a local stack-based buffer.
    *  - SDSORT_CACHE_NAMES will retain the sorted file listing in RAM. (Expensive!)
+   *  - SDSORT_DYNAMIC_RAM only uses RAM when the SD menu is visible. (Use with caution!)
    */
   //#define SDCARD_SORT_ALPHA
 
@@ -482,6 +483,7 @@
     #define SDSORT_USES_RAM    false  // Pre-allocate a static array for faster pre-sorting.
     #define SDSORT_USES_STACK  false  // Prefer the stack for pre-sorting to give back some SRAM. (Negated by next 2 options.)
     #define SDSORT_CACHE_NAMES false  // Keep sorted items in RAM longer for speedy performance. Most expensive option.
+    #define SDSORT_DYNAMIC_RAM false  // Use dynamic allocation (within SD menus). Least expensive option. Set SDSORT_LIMIT before use!
   #endif
 
   // Show a progress bar on HD44780 LCDs for SD printing

Marlin/example_configurations/WITBOX/Configuration_adv.h

@@ -463,6 +463,7 @@
    *  - SDSORT_USES_RAM provides faster sorting via a static directory buffer.
    *  - SDSORT_USES_STACK does the same, but uses a local stack-based buffer.
    *  - SDSORT_CACHE_NAMES will retain the sorted file listing in RAM. (Expensive!)
+   *  - SDSORT_DYNAMIC_RAM only uses RAM when the SD menu is visible. (Use with caution!)
    */
   //#define SDCARD_SORT_ALPHA
 
@@ -474,6 +475,7 @@
     #define SDSORT_USES_RAM    false  // Pre-allocate a static array for faster pre-sorting.
     #define SDSORT_USES_STACK  false  // Prefer the stack for pre-sorting to give back some SRAM. (Negated by next 2 options.)
     #define SDSORT_CACHE_NAMES false  // Keep sorted items in RAM longer for speedy performance. Most expensive option.
+    #define SDSORT_DYNAMIC_RAM false  // Use dynamic allocation (within SD menus). Least expensive option. Set SDSORT_LIMIT before use!
   #endif
 
   // Show a progress bar on HD44780 LCDs for SD printing

Marlin/example_configurations/delta/generic/Configuration_adv.h

@@ -465,6 +465,7 @@
    *  - SDSORT_USES_RAM provides faster sorting via a static directory buffer.
    *  - SDSORT_USES_STACK does the same, but uses a local stack-based buffer.
    *  - SDSORT_CACHE_NAMES will retain the sorted file listing in RAM. (Expensive!)
+   *  - SDSORT_DYNAMIC_RAM only uses RAM when the SD menu is visible. (Use with caution!)
    */
   //#define SDCARD_SORT_ALPHA
 
@@ -476,6 +477,7 @@
     #define SDSORT_USES_RAM    false  // Pre-allocate a static array for faster pre-sorting.
     #define SDSORT_USES_STACK  false  // Prefer the stack for pre-sorting to give back some SRAM. (Negated by next 2 options.)
     #define SDSORT_CACHE_NAMES false  // Keep sorted items in RAM longer for speedy performance. Most expensive option.
+    #define SDSORT_DYNAMIC_RAM false  // Use dynamic allocation (within SD menus). Least expensive option. Set SDSORT_LIMIT before use!
   #endif
 
   // Show a progress bar on HD44780 LCDs for SD printing

Marlin/example_configurations/delta/kossel_mini/Configuration_adv.h

@@ -465,6 +465,7 @@
    *  - SDSORT_USES_RAM provides faster sorting via a static directory buffer.
    *  - SDSORT_USES_STACK does the same, but uses a local stack-based buffer.
    *  - SDSORT_CACHE_NAMES will retain the sorted file listing in RAM. (Expensive!)
+   *  - SDSORT_DYNAMIC_RAM only uses RAM when the SD menu is visible. (Use with caution!)
    */
   //#define SDCARD_SORT_ALPHA
 
@@ -476,6 +477,7 @@
     #define SDSORT_USES_RAM    false  // Pre-allocate a static array for faster pre-sorting.
     #define SDSORT_USES_STACK  false  // Prefer the stack for pre-sorting to give back some SRAM. (Negated by next 2 options.)
     #define SDSORT_CACHE_NAMES false  // Keep sorted items in RAM longer for speedy performance. Most expensive option.
+    #define SDSORT_DYNAMIC_RAM false  // Use dynamic allocation (within SD menus). Least expensive option. Set SDSORT_LIMIT before use!
   #endif
 
   // Show a progress bar on HD44780 LCDs for SD printing

Marlin/example_configurations/delta/kossel_pro/Configuration_adv.h

@@ -470,6 +470,7 @@
    *  - SDSORT_USES_RAM provides faster sorting via a static directory buffer.
    *  - SDSORT_USES_STACK does the same, but uses a local stack-based buffer.
    *  - SDSORT_CACHE_NAMES will retain the sorted file listing in RAM. (Expensive!)
+   *  - SDSORT_DYNAMIC_RAM only uses RAM when the SD menu is visible. (Use with caution!)
    */
   //#define SDCARD_SORT_ALPHA
 
@@ -481,6 +482,7 @@
     #define SDSORT_USES_RAM    false  // Pre-allocate a static array for faster pre-sorting.
     #define SDSORT_USES_STACK  false  // Prefer the stack for pre-sorting to give back some SRAM. (Negated by next 2 options.)
     #define SDSORT_CACHE_NAMES false  // Keep sorted items in RAM longer for speedy performance. Most expensive option.
+    #define SDSORT_DYNAMIC_RAM false  // Use dynamic allocation (within SD menus). Least expensive option. Set SDSORT_LIMIT before use!
   #endif
 
   // Show a progress bar on HD44780 LCDs for SD printing

Marlin/example_configurations/delta/kossel_xl/Configuration_adv.h

@@ -465,6 +465,7 @@
    *  - SDSORT_USES_RAM provides faster sorting via a static directory buffer.
    *  - SDSORT_USES_STACK does the same, but uses a local stack-based buffer.
    *  - SDSORT_CACHE_NAMES will retain the sorted file listing in RAM. (Expensive!)
+   *  - SDSORT_DYNAMIC_RAM only uses RAM when the SD menu is visible. (Use with caution!)
    */
   //#define SDCARD_SORT_ALPHA
 
@@ -476,6 +477,7 @@
     #define SDSORT_USES_RAM    false  // Pre-allocate a static array for faster pre-sorting.
     #define SDSORT_USES_STACK  false  // Prefer the stack for pre-sorting to give back some SRAM. (Negated by next 2 options.)
     #define SDSORT_CACHE_NAMES false  // Keep sorted items in RAM longer for speedy performance. Most expensive option.
+    #define SDSORT_DYNAMIC_RAM false  // Use dynamic allocation (within SD menus). Least expensive option. Set SDSORT_LIMIT before use!
   #endif
 
   // Show a progress bar on HD44780 LCDs for SD printing

Marlin/example_configurations/makibox/Configuration_adv.h

@@ -463,6 +463,7 @@
    *  - SDSORT_USES_RAM provides faster sorting via a static directory buffer.
    *  - SDSORT_USES_STACK does the same, but uses a local stack-based buffer.
    *  - SDSORT_CACHE_NAMES will retain the sorted file listing in RAM. (Expensive!)
+   *  - SDSORT_DYNAMIC_RAM only uses RAM when the SD menu is visible. (Use with caution!)
    */
   //#define SDCARD_SORT_ALPHA
 
@@ -474,6 +475,7 @@
     #define SDSORT_USES_RAM    false  // Pre-allocate a static array for faster pre-sorting.
     #define SDSORT_USES_STACK  false  // Prefer the stack for pre-sorting to give back some SRAM. (Negated by next 2 options.)
     #define SDSORT_CACHE_NAMES false  // Keep sorted items in RAM longer for speedy performance. Most expensive option.
+    #define SDSORT_DYNAMIC_RAM false  // Use dynamic allocation (within SD menus). Least expensive option. Set SDSORT_LIMIT before use!
   #endif
 
   // Show a progress bar on HD44780 LCDs for SD printing

Marlin/example_configurations/tvrrug/Round2/Configuration_adv.h

@@ -463,6 +463,7 @@
    *  - SDSORT_USES_RAM provides faster sorting via a static directory buffer.
    *  - SDSORT_USES_STACK does the same, but uses a local stack-based buffer.
    *  - SDSORT_CACHE_NAMES will retain the sorted file listing in RAM. (Expensive!)
+   *  - SDSORT_DYNAMIC_RAM only uses RAM when the SD menu is visible. (Use with caution!)
    */
   //#define SDCARD_SORT_ALPHA
 
@@ -474,6 +475,7 @@
     #define SDSORT_USES_RAM    false  // Pre-allocate a static array for faster pre-sorting.
     #define SDSORT_USES_STACK  false  // Prefer the stack for pre-sorting to give back some SRAM. (Negated by next 2 options.)
     #define SDSORT_CACHE_NAMES false  // Keep sorted items in RAM longer for speedy performance. Most expensive option.
+    #define SDSORT_DYNAMIC_RAM false  // Use dynamic allocation (within SD menus). Least expensive option. Set SDSORT_LIMIT before use!
   #endif
 
   // Show a progress bar on HD44780 LCDs for SD printing