From 8ea79ddf6ab35ca48415d46f8c2ab09ed493b464 Mon Sep 17 00:00:00 2001
From: Marti Bolivar <mbolivar@leaflabs.com>
Date: Wed, 4 May 2011 13:22:00 -0400
Subject: Making micros() counter underrun safe.

Thanks, ala42!
---
 wirish/wirish_time.h | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/wirish/wirish_time.h b/wirish/wirish_time.h
index a0b1c11..d5349e3 100644
--- a/wirish/wirish_time.h
+++ b/wirish/wirish_time.h
@@ -27,8 +27,8 @@
  * @brief Timing and delay functions.
  */
 
-#ifndef _TIME_H
-#define _TIME_H
+#ifndef _TIME_H_
+#define _TIME_H_
 
 #include "libmaple.h"
 #include "nvic.h"
@@ -56,17 +56,15 @@ static inline uint32 micros(void) {
     uint32 cycle_cnt;
     uint32 res;
 
-    nvic_globalirq_disable();
-
-    cycle_cnt = systick_get_count();
-    ms = millis();
-
-    nvic_globalirq_enable();
+    do {
+        cycle_cnt = systick_get_count();
+        ms = millis();
+    } while (ms != millis());
 
     /* SYSTICK_RELOAD_VAL is 1 less than the number of cycles it
        actually takes to complete a SysTick reload */
     res = (ms * US_PER_MS) +
-        (SYSTICK_RELOAD_VAL + 1 - cycle_cnt)/CYCLES_PER_MICROSECOND;
+        (SYSTICK_RELOAD_VAL + 1 - cycle_cnt) / CYCLES_PER_MICROSECOND;
 
     return res;
 }
@@ -96,4 +94,3 @@ void delay(unsigned long ms);
 void delayMicroseconds(uint32 us);
 
 #endif
-
-- 
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