Add new system for startup.

Now instead of init() and main() being responsible for all
initialization, individual modules can link in their own
initialization routines.

There are 7 levels for these initializiation routines.

So far these are how the levels are defined

level 0 - Here the world is dark. Nothing is initialized.
          This level is responsible for initializing the
          system clock.

level 1 - The system clock has been configured, but nothing else. Not
          even global variables. This level is responsible for loading
          the data sections from flash and clearing the .bss section.

level 2 - USART2 is enabled and set to be the main kernel logging
          vehicle. From this point on klogf(...) can be used.

level 3 - The NVIC is reset to point to the flash. From this point
          on interrupts can be received. I expect this is where
          most core initialization routines will take place

levels 4 to 7 - User initializiation levels.

main - main() is called after all 8 initialization levels have executed,
       so in a sense main() is like a 9th initialization level, except
       that there is can be only one main() routine whereas there can be
       multiple initalization routines per level.

1 files changed, 67 insertions, 0 deletions

diff --git a/02-usart/include/kern/init.h b/02-usart/include/kern/init.h
new file mode 100644
index 0000000..737b85f
--- /dev/null
+++ b/02-usart/include/kern/init.h
@@ -0,0 +1,67 @@
+#ifndef INIT_H_
+#define INIT_H_
+
+/** Globals annotated with _no_init will not be set during init1 bootup
+ * where the data segement is loaded from flash and the bss segment is
+ * cleared.
+ *
+ * This is useful for routines that run in the init0 boot procedure
+ * that need persistent globals.
+ *
+ * Note that initializing a global annotated with _no_init will have
+ * no effect as the variable will remain uninitialized until explicitly
+ * set by by the program.
+ */
+#define _no_init \
+  __attribute((__section__(".noinit")))
+
+#define init0 \
+  static void init0fn(); \
+  static __attribute((__section__(".init0"))) \
+  __attribute((__used__)) \
+  void(*init0_ptr)() = init0fn; \
+  static void init0fn
+#define init1 \
+  static void init1fn(); \
+  static __attribute((__section__(".init1"))) \
+  __attribute((__used__)) \
+  void(*init1_ptr)() = init1fn; \
+  static void init1fn
+#define init2 \
+  static void init2fn(); \
+  static __attribute((__section__(".init2"))) \
+  __attribute((__used__)) \
+  void(*init2_ptr)() = init2fn; \
+  static void init2fn
+#define init3 \
+  static void init3fn(); \
+  static __attribute((__section__(".init3"))) \
+  __attribute((__used__)) \
+  void(*init3_ptr)() = init3fn; \
+  static void init3fn
+#define init4 \
+  static void init4fn(); \
+  static __attribute((__section__(".init4"))) \
+  __attribute((__used__)) \
+  void(*init4_ptr)() = init4fn; \
+  static void init4fn
+#define init5 \
+  static void init5fn(); \
+  static __attribute((__section__(".init5"))) \
+  __attribute((__used__)) \
+  void(*init5_ptr)() = init5fn; \
+  static void init5fn
+#define init6 \
+  static void init6fn(); \
+  static __attribute((__section__(".init6"))) \
+  __attribute((__used__)) \
+  void(*init6_ptr)() = init6fn; \
+  static void init6fn
+#define init7 \
+  static void init7fn(); \
+  static __attribute((__section__(".init7"))) \
+  __attribute((__used__)) \
+  void(*init7_ptr)() = init7fn; \
+  static void init7fn
+
+#endif /* INIT_H_ */