more tests

canvas.h

@@ -8,20 +8,20 @@
 #define CANVAS_HEIGHT 11 
 
 typedef struct {
-  uint8_t width;
-  uint8_t height;
-  uint8_t size;
-  uint8_t *canvas;
+  const uint8_t width;
+  const uint8_t height;
+  const uint8_t size;
+  uint8_t * const canvas;
 } canvas_t;
 
 void canvasInit();
 void canvasClear();
 void canvasSetAll(uint8_t color);
-canvas_t *canvasGet();
 void canvasShow();
 void canvasSetPixel(uint8_t column, uint8_t row, uint8_t color);
 void canvasWipeRow(uint8_t row);
 uint8_t canvasIsRowFilled(uint8_t row);
 
+extern const canvas_t canvas;
 
 #endif // _CANVAS_H_