initial clock mode impl

GUI/GUI.h

@@ -0,0 +1,15 @@
+#ifndef __GUI_H
+#define __GUI_H
+
+#include <stdint.h>
+#include "EPD_driver.h"
+
+typedef enum {
+    MODE_NONE = 0,
+    MODE_CALENDAR = 1,
+    MODE_CLOCK = 2,
+} display_mode_t;
+
+void DrawGUI(epd_model_t *epd, uint32_t timestamp, display_mode_t mode);
+
+#endif