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, 19 insertions, 0 deletions

diff --git a/02-usart/linker/linker_script.ld b/02-usart/linker/linker_script.ld
index 348d03b..9a9f5b3 100644
--- a/02-usart/linker/linker_script.ld
+++ b/02-usart/linker/linker_script.ld
@@ -23,8 +23,27 @@ SECTIONS
     *(.data);
     DATA_SEGMENT_STOP = .;
 
+    INIT_ROUTINES_FLASH_START =
+       LOADADDR(.data) + (DATA_SEGMENT_STOP - DATA_SEGMENT_START);
+
+    INITS_START = .;
+    *(.init0);
+    *(.init1);
+    *(.init2);
+    *(.init3);
+    *(.init4);
+    *(.init5);
+    *(.init6);
+    *(.init7);
+    INITS_END = .;
+
+    INIT_ROUTINES_FLASH_STOP =
+       LOADADDR(.data) + (INITS_END - DATA_SEGMENT_START);
+
     /* Align by 4 so we can optimize the copier to use uint32's. */
     . = ALIGN(0x04);
+
+    *(.noinit);
   } >sram1 AT>flash
 
   BSS_START = .;