Dot Matrix: Replace std::map to avoid excessive init heap usage.

drivers/ltp305/dotfont.hpp

@@ -8,10 +8,11 @@ namespace pimoroni {
   static const uint8_t DOT_CHAR_WIDTH = 5;
 
   struct DotChar {
+    uint16_t code;
     uint8_t data[DOT_CHAR_WIDTH];
   };
 
-  static const std::map<uint16_t, DotChar> dotfont = {
+  static const DotChar dotfont[] = {
     {32, {0x00, 0x00, 0x00, 0x00, 0x00}},   // (space)
     {33, {0x00, 0x00, 0x5f, 0x00, 0x00}},   // !
     {34, {0x00, 0x07, 0x00, 0x07, 0x00}},   // "

drivers/ltp305/ltp305.cpp

@@ -64,13 +64,18 @@ namespace pimoroni {
   }
 
   void LTP305::set_character(uint8_t x, uint16_t ch) {
-    std::map<uint16_t, DotChar>::const_iterator it = dotfont.find(ch);
+    uint8_t *data = nullptr;
+    for(auto c : dotfont) {
+      if(c.code == ch) {
+        data = &c.data[0];
+        break;
+      }
+    }
 
-    if(it != dotfont.end()) {
-      DotChar dchar = it->second;
+    if(data) {
       for(uint8_t cx = 0; cx < DOT_CHAR_WIDTH; cx++) {
         for(uint8_t cy = 0; cy < HEIGHT; cy++) {
-          uint8_t c = dchar.data[cx] & (0b1 << cy);
+          uint8_t c = data[cx] & (0b1 << cy);
           set_pixel(x + cx, cy, c);
         }
       }