feat(radio): move inputNames to arena with sparse side-array indexing

Replace the fixed char inputNames[MAX_INPUTS][LEN_INPUT_NAME] array in
ModelData with a sparse arena section (ARENA_INPUT_NAMES) indexed by a
uint8_t inputNameIndex[MAX_INPUTS] side-array. Only named inputs consume
arena space; 0xFF in the index means "no name".

Accessor API: inputName() for O(1) read, inputNameAlloc() for
alloc-on-demand, inputNameClear() with swap-with-last compaction.

YAML serialization uses YAML_IDX_CUST so the custom index read/write
maps between sparse arena slots and YAML input numbers directly — no
expand/compact buffers needed.

Saves 96 bytes (color) / 64 bytes (B&W) from ModelData for typical
models that name only a few inputs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: raphaelcoeffic

radio/src/datastructs.h

@@ -89,35 +89,35 @@ static inline void check_struct()
 #endif
 
 #if defined(RADIO_TPRO) || defined(RADIO_TPROV2) || defined(RADIO_BUMBLEBEE)
-  CHKSIZE(ModelData, 1781);
+  CHKSIZE(ModelData, 1717);
 #elif defined(RADIO_FAMILY_T20)
-  CHKSIZE(ModelData, 1781);
+  CHKSIZE(ModelData, 1717);
 #elif defined(RADIO_GX12)
-  CHKSIZE(ModelData, 1845);
+  CHKSIZE(ModelData, 1781);
 #elif defined(PCBX9E)
-  CHKSIZE(ModelData, 2225);
+  CHKSIZE(ModelData, 2129);
 #elif defined(PCBX9D) || defined(PCBX9DP)
-  CHKSIZE(ModelData, 2224);
+  CHKSIZE(ModelData, 2128);
 #elif defined(PCBX7) || defined(PCBXLITE) || defined(PCBX9LITE) || defined(RADIO_T14) || defined(RADIO_T12MAX)
-  CHKSIZE(ModelData, 1755);
+  CHKSIZE(ModelData, 1691);
 #elif defined(PCBPL18)
   #if defined(RADIO_NB4P) || defined(RADIO_NV14_FAMILY)
-    CHKSIZE(ModelData, 2221);
+    CHKSIZE(ModelData, 2125);
   #else
-    CHKSIZE(ModelData, 2223);
+    CHKSIZE(ModelData, 2127);
   #endif
 #elif defined(PCBST16) || defined(RADIO_T15PRO) || defined(RADIO_TX15)
-  CHKSIZE(ModelData, 2837);
+  CHKSIZE(ModelData, 2741);
 #elif defined(PCBPA01)
-  CHKSIZE(ModelData, 2814);
+  CHKSIZE(ModelData, 2718);
 #elif defined(RADIO_T15)
-  CHKSIZE(ModelData, 2249);
+  CHKSIZE(ModelData, 2153);
 #elif defined(RADIO_TX16SMK3)
-  CHKSIZE(ModelData, 2838);
+  CHKSIZE(ModelData, 2742);
 #elif defined(RADIO_H7RS)
   // CHKSIZE()
 #elif defined(PCBHORUS)
-  CHKSIZE(ModelData, 2223);
+  CHKSIZE(ModelData, 2127);
 #else
   #error CHKSIZE not set up
 #endif

radio/src/datastructs_private.h

@@ -766,6 +766,14 @@ PACK(struct USBJoystickChData {
 #endif
 });
 
+// YAML-visible struct for input name strings (adapts to LEN_INPUT_NAME).
+// CUST_IDX provides custom index read/write so the YAML index is the input
+// number while the arena stores names sparsely.
+PACK(struct InputNameStr {
+  CUST_IDX(inputNames, r_input_name_idx, w_input_name_idx);
+  char val[LEN_INPUT_NAME];
+});
+
 PACK(struct ModelData {
   CUST_ATTR(semver,nullptr,w_semver);
   ModelHeader header;
@@ -834,7 +842,8 @@ PACK(struct ModelData {
 
   SCRIPT_DATA
 
-  NOBACKUP(char inputNames[MAX_INPUTS][LEN_INPUT_NAME]);
+  NOBACKUP(uint8_t inputNameIndex[MAX_INPUTS]) SKIP;
+  CUST_EXTERN_ARRAY_NOIDX(inputNames, struct_InputNameStr, MAX_INPUTS, yaml_drv_input_names);
   NOBACKUP(potwarnen_t potsWarnEnabled);
   NOBACKUP(int8_t potsWarnPosition[MAX_POTS]);
 

radio/src/expos.cpp

@@ -23,9 +23,12 @@
 #include "tasks/mixer_task.h"
 #include "hal/adc_driver.h"
 #include "model_arena.h"
+#include "dataconstants.h"
 
 #include "edgetx.h"
 
+#include <string.h>
+
 static uint8_t _nb_expo_lines;
 
 ExpoData* expoAddress(uint8_t idx) {
@@ -81,7 +84,7 @@ void deleteExpo(uint8_t idx)
   g_modelArena.deleteFromSection(ARENA_EXPOS, idx, sizeof(ExpoData));
 
   if (!isInputAvailable(input)) {
-    memclear(&g_model.inputNames[input], LEN_INPUT_NAME);
+    inputNameClear(input);
   }
   mixerTaskStart();
 
@@ -174,3 +177,73 @@ void updateExpoCount()
 {
   _nb_expo_lines = _countExpoLines();
 }
+
+// ---------------------------------------------------------------------------
+// Input name accessors (arena-backed, sparse via side-array index)
+// ---------------------------------------------------------------------------
+
+#define INPUT_NAME_NO_SLOT 0xFF
+
+void inputNameIndexReset()
+{
+  memset(g_model.inputNameIndex, INPUT_NAME_NO_SLOT,
+         sizeof(g_model.inputNameIndex));
+}
+
+static inline char* _inputNameSlot(uint8_t slot)
+{
+  return reinterpret_cast<char*>(
+      g_modelArena.sectionBase(ARENA_INPUT_NAMES)) + slot * LEN_INPUT_NAME;
+}
+
+const char* inputName(uint8_t input)
+{
+  uint8_t slot = g_model.inputNameIndex[input];
+  if (slot == INPUT_NAME_NO_SLOT)
+    return nullptr;
+  return _inputNameSlot(slot);
+}
+
+bool hasInputName(uint8_t input)
+{
+  return g_model.inputNameIndex[input] != INPUT_NAME_NO_SLOT;
+}
+
+char* inputNameAlloc(uint8_t input)
+{
+  uint8_t slot = g_model.inputNameIndex[input];
+  if (slot != INPUT_NAME_NO_SLOT)
+    return _inputNameSlot(slot);
+
+  // Append a new slot
+  uint16_t count = g_modelArena.sectionCount(ARENA_INPUT_NAMES);
+  if (!g_modelArena.ensureSectionCapacity(ARENA_INPUT_NAMES, count + 1))
+    return nullptr;
+
+  g_model.inputNameIndex[input] = count;
+  return _inputNameSlot(count);
+}
+
+void inputNameClear(uint8_t input)
+{
+  uint8_t slot = g_model.inputNameIndex[input];
+  if (slot == INPUT_NAME_NO_SLOT)
+    return;
+
+  uint16_t count = g_modelArena.sectionCount(ARENA_INPUT_NAMES);
+  uint16_t lastSlot = count - 1;
+
+  if (slot != lastSlot) {
+    // Find which input owns the last slot and swap
+    for (uint8_t i = 0; i < MAX_INPUTS; i++) {
+      if (g_model.inputNameIndex[i] == lastSlot) {
+        memcpy(_inputNameSlot(slot), _inputNameSlot(lastSlot), LEN_INPUT_NAME);
+        g_model.inputNameIndex[i] = slot;
+        break;
+      }
+    }
+  }
+
+  g_model.inputNameIndex[input] = INPUT_NAME_NO_SLOT;
+  g_modelArena.trimSectionTo(ARENA_INPUT_NAMES, lastSlot);
+}

radio/src/expos.h

@@ -49,3 +49,23 @@ uint8_t getExpoCount();
 // Should only be called from storage
 // right after a model has been loaded
 void updateExpoCount();
+
+// --- Input name accessors (arena-backed, sparse) ---
+
+// Read-only lookup. Returns pointer to name or nullptr if input has no name.
+const char* inputName(uint8_t input);
+
+// Returns true if the input has a name allocated.
+bool hasInputName(uint8_t input);
+
+// Ensure a name slot exists for 'input' and return a writable pointer.
+// Allocates a new arena slot if needed. Returns nullptr on arena exhaustion.
+char* inputNameAlloc(uint8_t input);
+
+// Remove the name for 'input', freeing the arena slot (swap-with-last).
+void inputNameClear(uint8_t input);
+
+// Clear the entire inputNameIndex (set all to 0xFF).
+// Called on model init / clear before loading names.
+void inputNameIndexReset();
+

radio/src/gui/128x64/model_input_edit.cpp

@@ -88,7 +88,7 @@ void menuModelExpoOne(event_t event)
     switch (i) {
       case EXPO_FIELD_INPUT_NAME:
         editSingleName(EXPO_ONE_2ND_COLUMN, y,
-                       STR_INPUTNAME, g_model.inputNames[ed->chn],
+                       STR_INPUTNAME, inputNameAlloc(ed->chn),
                        LEN_INPUT_NAME, event, (attr != 0), old_editMode);
         break;
 

radio/src/gui/212x64/model_input_edit.cpp

@@ -90,7 +90,7 @@ void menuModelExpoOne(event_t event)
     switch (i) {
       case EXPO_FIELD_INPUT_NAME:
         editSingleName(EXPO_ONE_2ND_COLUMN, y, STR_INPUTNAME,
-                       g_model.inputNames[ed->chn], LEN_INPUT_NAME, event, attr,
+                       inputNameAlloc(ed->chn), LEN_INPUT_NAME, event, attr,
                        old_editMode);
         break;
 

radio/src/gui/colorlcd/model/input_edit.cpp

@@ -158,7 +158,7 @@ void InputEditWindow::buildBody(Window* form)
   // Input Name
   auto line = form->newLine(grid);
   new StaticText(line, rect_t{}, STR_INPUTNAME);
-  new ModelTextEdit(line, rect_t{}, g_model.inputNames[input->chn],
+  new ModelTextEdit(line, rect_t{}, inputNameAlloc(input->chn),
                     LEN_INPUT_NAME,
                     [=]() {
                       setTitle();

radio/src/gui/common/stdlcd/draw_functions.cpp

@@ -561,9 +561,11 @@ void drawSource(coord_t x, coord_t y, const SourceRef& ref, LcdFlags att)
       break;
 
     case SOURCE_TYPE_INPUT:
+    {
+      const char* iName = inputName(idx);
       if (att & RIGHT) {
-        if (g_model.inputNames[idx][0])
-          lcdDrawSizedText(x, y, g_model.inputNames[idx], LEN_INPUT_NAME, att);
+        if (iName && iName[0])
+          lcdDrawSizedText(x, y, iName, LEN_INPUT_NAME, att);
         else
           lcdDrawNumber(x, y, idx + 1, att|LEADING0, 2);
         x = lcdLastLeftPos - 5;
@@ -578,12 +580,13 @@ void drawSource(coord_t x, coord_t y, const SourceRef& ref, LcdFlags att)
         }
         lcdDrawChar(x+1, y+1, CHR_INPUT, TINSIZE);
         lcdDrawSolidFilledRect(x, y, 5, 7);
-        if (g_model.inputNames[idx][0])
-          lcdDrawSizedText(x+6, y, g_model.inputNames[idx], LEN_INPUT_NAME, att);
+        if (iName && iName[0])
+          lcdDrawSizedText(x+6, y, iName, LEN_INPUT_NAME, att);
         else
           lcdDrawNumber(x+6, y, idx + 1, att|LEADING0, 2);
       }
       break;
+    }
 
 #if defined(LUA_INPUTS)
     case SOURCE_TYPE_LUA:

radio/src/lua/api_model.cpp

@@ -654,7 +654,8 @@ static int luaModelGetInput(lua_State *L)
     ExpoData * expo = expoAddress(first+idx);
     lua_newtable(L);
     lua_pushtablenstring(L, "name", expo->name);
-    lua_pushtablenstring(L, "inputName", g_model.inputNames[chn]);
+    const char* iName = inputName(chn);
+    lua_pushtablenstring(L, "inputName", iName ? iName : "");
     lua_pushtableinteger(L, "source", expo->srcRaw.toUint32());
     lua_pushtableinteger(L, "scale", expo->scale);
     lua_pushtableinteger(L, "weight", valueOrSourceToLuaInt(expo->weight));
@@ -707,7 +708,11 @@ static int luaModelInsertInput(lua_State *L)
       }
       else if (!strcmp(key, "inputName")) {
         const char * name = luaL_checkstring(L, -1);
-        strncpy(g_model.inputNames[chn], name, LEN_INPUT_NAME);
+        if (name[0]) {
+          strncpy(inputNameAlloc(chn), name, LEN_INPUT_NAME);
+        } else {
+          inputNameClear(chn);
+        }
       }
       else if (!strcmp(key, "source")) {
         expo->srcRaw = SourceRef::fromUint32(luaL_checkinteger(L, -1));

radio/src/model_arena.cpp

@@ -39,6 +39,7 @@ static const uint8_t modelElemSizes[MODEL_ARENA_NUM_SECTIONS] = {
   sizeof(FlightModeData),
   sizeof(GVarData),
   sizeof(gvar_t),
+  LEN_INPUT_NAME,
 };
 
 const ArenaDesc modelArenaDesc = { MODEL_ARENA_NUM_SECTIONS, modelElemSizes };