From b5d17bb620acfb5cdeb9838829560147e1b62d5c Mon Sep 17 00:00:00 2001
From: Atis Elsts <atis.elsts@gmail.com>
Date: Tue, 18 Aug 2015 15:30:20 +0200
Subject: [PATCH] ContikiMAC: use RTIMER_GUARD_TIME #define to avoid
 accidentally scheduling a rtimer in the past on platforms with fast rtimer
 ticks

---
 core/net/mac/contikimac/contikimac.c | 16 +++++++++++-----
 core/sys/rtimer.h                    | 10 ++++++++++
 2 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/core/net/mac/contikimac/contikimac.c b/core/net/mac/contikimac/contikimac.c
index 186ce743b..104478282 100644
--- a/core/net/mac/contikimac/contikimac.c
+++ b/core/net/mac/contikimac/contikimac.c
@@ -296,14 +296,18 @@ static void
 schedule_powercycle(struct rtimer *t, rtimer_clock_t time)
 {
   int r;
+  rtimer_clock_t now;
 
   if(contikimac_is_on) {
 
-    if(RTIMER_CLOCK_LT(RTIMER_TIME(t) + time, RTIMER_NOW() + 2)) {
-      time = RTIMER_NOW() - RTIMER_TIME(t) + 2;
+    time += RTIMER_TIME(t);
+    now = RTIMER_NOW();
+    if(RTIMER_CLOCK_LT(time, now + RTIMER_GUARD_TIME)) {
+      time = now + RTIMER_GUARD_TIME;
     }
 
-    r = rtimer_set(t, RTIMER_TIME(t) + time, 1, powercycle_wrapper, NULL);
+    r = rtimer_set(t, time, 1, powercycle_wrapper, NULL);
+
     if(r != RTIMER_OK) {
       PRINTF("schedule_powercycle: could not set rtimer\n");
     }
@@ -314,11 +318,13 @@ static void
 schedule_powercycle_fixed(struct rtimer *t, rtimer_clock_t fixed_time)
 {
   int r;
+  rtimer_clock_t now;
 
   if(contikimac_is_on) {
 
-    if(RTIMER_CLOCK_LT(fixed_time, RTIMER_NOW() + 1)) {
-      fixed_time = RTIMER_NOW() + 1;
+    now = RTIMER_NOW();
+    if(RTIMER_CLOCK_LT(fixed_time, now + RTIMER_GUARD_TIME)) {
+      fixed_time = now + RTIMER_GUARD_TIME;
     }
 
     r = rtimer_set(t, fixed_time, 1, powercycle_wrapper, NULL);
diff --git a/core/sys/rtimer.h b/core/sys/rtimer.h
index 11dde5fa1..91c23b932 100644
--- a/core/sys/rtimer.h
+++ b/core/sys/rtimer.h
@@ -151,6 +151,16 @@ void rtimer_arch_schedule(rtimer_clock_t t);
 
 #define RTIMER_SECOND RTIMER_ARCH_SECOND
 
+/* RTIMER_GUARD_TIME is the minimum amount of rtimer ticks between
+   the current time and the future time when a rtimer is scheduled.
+   Necessary to avoid accidentally scheduling a rtimer in the past
+   on platforms with fast rtimer ticks. Should be >= 2. */
+#ifdef RTIMER_CONF_GUARD_TIME
+#define RTIMER_GUARD_TIME RTIMER_CONF_GUARD_TIME
+#else /* RTIMER_CONF_GUARD_TIME */
+#define RTIMER_GUARD_TIME (RTIMER_ARCH_SECOND >> 14)
+#endif /* RTIMER_CONF_GUARD_TIME */
+
 #endif /* RTIMER_H_ */
 
 /** @} */