Use the builtin RTC and display it

Its roughly %15 fast, and initializes to zero, but the display
currently shows HH:MM:SS AM/PM.

macros.h

@@ -27,8 +27,22 @@
 
 #include <assert.h>
 
+/**
+ * I'll probably regret writing all of these at some point.
+ */
+
 #define ARRAY_SIZE(x) (sizeof(x) / sizeof(x[0]))
 
+#define MIN(a,b) ((a > b) ? (b) : (a))
+#define MAX(a,b) ((a < b) ? (b) : (a))
+
+/*
+ * For usage with STM32 libraries
+ */
+
+#define STM32_FIELD(x, name)                    \
+    ((x) & name##_Msk) >> (name##_Pos)
+
 /*
  * Bitwise Operations
  */