A basic blink program that works off of interrupts.

  - The init() function renamed to on_reset()
  - on_reset() now responsible for tight-looping at the end
  - on_reset() now set the VTable offset to the base of the FLASH
  - included exhaustive list of irqs in isrs.i
  - interrupt routines by default flash a code indicating their
    isr number.
  - interrupt routines are weak-linked allowing the programmer
    to override them at-will.

1 files changed, 45 insertions, 0 deletions

diff --git a/02-usart/src/init.c b/02-usart/src/init.c
new file mode 100644
index 0000000..70703aa
--- /dev/null
+++ b/02-usart/src/init.c
@@ -0,0 +1,45 @@
+#include "arch.h"
+#include "system.h"
+
+/* Forward-declare the main function. This is implemented in main.c. */
+void main();
+
+/* These are defined in the linker script. */
+extern uint32_t INIT_DATA_VALUES;
+extern uint32_t DATA_SEGMENT_START;
+extern uint32_t DATA_SEGMENT_STOP;
+extern uint32_t BSS_START;
+extern uint32_t BSS_END;
+
+/*
+ * Runs before main. Initializes the data and bss segments by loading them
+ * into memory.
+ */
+_Noreturn void on_reset()
+{
+  uint32_t* src;
+  uint32_t* dest;
+
+  src = &INIT_DATA_VALUES;
+  dest = &DATA_SEGMENT_START;
+
+  /* Copy the values from flash into the data segment. */
+  while (dest != &DATA_SEGMENT_STOP) {
+    *(dest++) = *(src++);
+  }
+
+  /* Everything in the BSS segment is set to zero. */
+  dest = &BSS_START;
+  while (dest != &BSS_END) {
+    *(dest++) = 0;
+  }
+
+  /* Set the vector offset table to be at the start
+   * of FLASH memory. */
+  SCB.vto_r = 0x08000000;
+
+  /* Jump to main. */
+  main();
+
+  for(;;);
+}