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, 11 insertions, 0 deletions

diff --git a/02-usart/src/arch/stm32l4xxx/peripherals/clock.c b/02-usart/src/arch/stm32l4xxx/peripherals/clock.c
index 1029d39..9051572 100644
--- a/02-usart/src/arch/stm32l4xxx/peripherals/clock.c
+++ b/02-usart/src/arch/stm32l4xxx/peripherals/clock.c
@@ -5,10 +5,13 @@
 #include "arch/stm32l4xxx/peripherals/clock.h"
 #include "arch/stm32l4xxx/peripherals/flash.h"
 
+#include "kern/init.h"
+
 #include <stdint.h>
 
 #define TIMEOUT 10000
 
+
 int pll_off()
 {
   uint32_t c;
@@ -66,8 +69,16 @@ int configure_pll(
   return 0;
 }
 
+static _no_init uint8_t clock_mHz;
+uint8_t get_clock_mhz()
+{
+  return clock_mHz;
+}
+
 int set_system_clock_MHz(uint8_t mhz)
 {
+  clock_mHz = mhz;
+
   /* Set the source of the system colck to MSI temporarily. */
   set_system_clock_src(SYSTEM_CLOCK_SRC_MSI);