systick testing and simplification

ripped out marti's SystemTick for the sake of simplicity and added a
systick_resume function to libmaple. new example program demonstrates
the functionality, also demonstrates micros()/USB bug

2 files changed, 8 insertions, 0 deletions

diff --git a/libmaple/systick.c b/libmaple/systick.c
index 456ac2f..9fbb152 100644
--- a/libmaple/systick.c
+++ b/libmaple/systick.c
@@ -58,6 +58,13 @@ void systick_disable() {
   __write(SYSTICK_CSR, SYSTICK_SRC_HCLK);
 }
 
+void systick_resume() {
+  /* re-enable init registers without changing relead_val */
+  __write(SYSTICK_CSR, SYSTICK_SRC_HCLK |
+                       SYSTICK_ENABLE   |
+                       SYSTICK_TICKINT);
+}
+
 void SysTickHandler(void) {
     systick_timer_millis++;
 }
diff --git a/libmaple/systick.h b/libmaple/systick.h
index 86284f8..80e2fde 100644
--- a/libmaple/systick.h
+++ b/libmaple/systick.h
@@ -44,6 +44,7 @@ extern "C"{
 
 void systick_init(uint32 reload_val);
 void systick_disable();
+void systick_resume();
 
 static inline uint32 systick_get_count(void) {
     return __read(SYSTICK_CNT);