Updates to how the ISR updates work.

4 files changed, 28 insertions, 4 deletions

diff --git a/include/isr_vector.h b/include/isr_vector.h
index bd5786a..65359a5 100644
--- a/include/isr_vector.h
+++ b/include/isr_vector.h
@@ -10,6 +10,7 @@ void default_irq_handler(void);
 
 /** Weakly defined interrput service routine vectors. These just alias to
  * default_irq_handler if not overridden. */
+void irq_on_reset(void);
 void irq_on_nmi(void);
 void irq_on_exc(void);
 void irq_on_systick(void);
@@ -33,4 +34,20 @@ void irq_on_uart2(void);
 void irq_on_uart3(void);
 void irq_on_wdog_bat(void);
 
-#define IRQ(name) void __attribute__((__section__(".isr_vector"))) name(void)
+/*
+ * Macro to define an interrput service routine.
+ */
+#define IRQ(name)                                                             \
+  /* Real interrupt service routine. This contains most of the code to handle \
+   * the interrupt. */                                                        \
+  static void __attribute__((noinline)) _real__irq_on_##name(void);           \
+  /* The actual routine that's jumped to. It's soley responsible for jumping  \
+   * to the real handler (which requires multiple instructions because it's a \
+   * long jump). This stub is compiled and linked promimal to the ISR vector. \
+   */                                                                         \
+  void __attribute__((interrupt))                                             \
+  __attribute__((__section__(".isr_vector"))) irq_on_##name(void)             \
+  {                                                                           \
+    _real__irq_on_##name();                                                   \
+  }                                                                           \
+  static void __attribute__((noinline)) _real__irq_on_##name(void)
diff --git a/src/blinky.c b/src/blinky.c
index 9f89238..355b479 100644
--- a/src/blinky.c
+++ b/src/blinky.c
@@ -12,9 +12,6 @@
 void delay(void);
 
 void main(void);
-IRQ(irq_on_systick) {
-  main();
-}
 
 uint32_t collatz(uint32_t n)
 {
@@ -78,3 +75,11 @@ void main(void)
     delay();
   }
 }
+
+IRQ(systick) {
+  collatz(5);
+}
+
+IRQ(exc) {}
+
+IRQ(nmi) {}
diff --git a/src/init.c b/src/init.c
index a81ce1d..30e2c6d 100644
--- a/src/init.c
+++ b/src/init.c
@@ -16,6 +16,7 @@ default_irq_handler(void)
       weak, alias("default_irq_handler"), __section__(".isr_vector"))) \
   irq(void)
 
+WEAK_IRQ(irq_on_reset);
 WEAK_IRQ(irq_on_nmi);
 WEAK_IRQ(irq_on_exc);
 WEAK_IRQ(irq_on_systick);
diff --git a/src/isr.s b/src/isr.s
index 6a9e6cf..065450d 100644
--- a/src/isr.s
+++ b/src/isr.s
@@ -8,6 +8,7 @@ j on_reset /* first instruction. Should jump directly to on_reset */
 isr_vector:
 .align 4
 .word 0
+  j irq_on_reset
   j irq_on_nmi
   j irq_on_exc