From a6c2c52fb21d94c1dcf43d1c14234e12221f1d26 Mon Sep 17 00:00:00 2001
From: Hyungsin <hskim@berkeley.edu>
Date: Thu, 4 Jan 2018 17:45:23 -0800
Subject: [PATCH] properly sync different timers

---
 cpu/samd21/periph/pm.c              |  2 ++
 sys/include/xtimer/implementation.h | 33 ++++++++++++++++++-----------
 sys/xtimer/xtimer_core.c            |  8 +++++++
 3 files changed, 31 insertions(+), 12 deletions(-)

diff --git a/cpu/samd21/periph/pm.c b/cpu/samd21/periph/pm.c
index e99babfbf5a6..4577278c64cc 100644
--- a/cpu/samd21/periph/pm.c
+++ b/cpu/samd21/periph/pm.c
@@ -24,6 +24,7 @@
  */
 
 #include "periph/pm.h"
+#include "xtimer.h"
 
 #define ENABLE_DEBUG (0)
 #include "debug.h"
@@ -61,6 +62,7 @@ void pm_set(unsigned mode)
              * Potential Wake Up sources: asynchronous
              */
             deep = 1;
+            xtimer_sync = false;
             break;
         case 1:
             /* Sleep mode Idle 2
diff --git a/sys/include/xtimer/implementation.h b/sys/include/xtimer/implementation.h
index f9bc40bfbba7..15ff7529a4a6 100644
--- a/sys/include/xtimer/implementation.h
+++ b/sys/include/xtimer/implementation.h
@@ -36,6 +36,7 @@ extern volatile uint32_t _xtimer_high_cnt;
 #if (XTIMER_HZ < 1000000ul) && (STIMER_HZ >= 1000000ul)
 extern volatile uint32_t prev_s;
 extern volatile uint32_t prev_x;
+extern volatile bool     xtimer_sync;
 #endif
 
 
@@ -123,19 +124,26 @@ static inline uint32_t _xtimer_now(void)
     return latched_high_cnt | now;
 #else
 #if (XTIMER_HZ < 1000000ul) && (STIMER_HZ >= 1000000ul)
-    uint64_t diff_s;
-    uint32_t now_s;
+    if (!xtimer_sync) {
+        prev_x = _xtimer_lltimer_now();
+        prev_s = _stimer_lltimer_now();
+        xtimer_sync = true;
+        return prev_x;
+    } else {
+        uint64_t diff_s;
+        uint32_t now_s;
     
-    do {
-        now_s = _stimer_lltimer_now();
-        if (now_s >= prev_s) {
-            diff_s = now_s - prev_s;
-        } else {
-            diff_s = (0xFFFFFFFF-prev_s) + now_s;
-        }
-    } while (diff_s < STIMER_HZ/XTIMER_HZ); 
-
-    return _xtimer_lltimer_mask(prev_x + (uint32_t)(diff_s*XTIMER_HZ/STIMER_HZ));
+        do {
+            now_s = _stimer_lltimer_now();
+            if (now_s >= prev_s) {
+                diff_s = now_s - prev_s;
+            } else {
+                diff_s = (0xFFFFFFFF-prev_s) + now_s;
+            }
+        } while (diff_s < STIMER_HZ/XTIMER_HZ); 
+
+        return _xtimer_lltimer_mask(prev_x + (uint32_t)(diff_s*XTIMER_HZ/STIMER_HZ));
+    }
 #else
     return _xtimer_lltimer_now();
 #endif
@@ -177,6 +185,7 @@ static inline void _xtimer_spin(uint32_t offset) {
 #if (XTIMER_HZ < 1000000ul) && (STIMER_HZ >= 1000000ul)
     prev_x = _xtimer_lltimer_now();
     prev_s = _stimer_lltimer_now();
+    xtimer_sync = true;
 #endif
 }
 
diff --git a/sys/xtimer/xtimer_core.c b/sys/xtimer/xtimer_core.c
index 0271d5c422a6..653ba0f52617 100644
--- a/sys/xtimer/xtimer_core.c
+++ b/sys/xtimer/xtimer_core.c
@@ -39,6 +39,7 @@ volatile uint32_t _xtimer_high_cnt = 0;
 #if (XTIMER_HZ < 1000000ul) && (STIMER_HZ >= 1000000ul)
 volatile uint32_t prev_s = 0xffffffff;
 volatile uint32_t prev_x = 0xffffffff;
+volatile bool xtimer_sync = false;
 #endif
 
 static inline void xtimer_spin_until(uint32_t value);
@@ -73,6 +74,7 @@ static inline void xtimer_spin_until(uint32_t target) {
 #if (XTIMER_HZ < 1000000ul) && (STIMER_HZ >= 1000000ul)
     prev_s = _stimer_lltimer_now();
     prev_x = _xtimer_lltimer_now();
+    xtimer_sync = true;
 #endif
 }
 
@@ -88,6 +90,7 @@ void xtimer_init(void)
     timer_init(STIMER_DEV, STIMER_HZ, _periph_timer_callback, NULL);
     prev_s = _stimer_lltimer_now();
     prev_x = _xtimer_lltimer_now();
+    xtimer_sync = true;
 #endif
     /* register initial overflow tick */
     _lltimer_set(0xFFFFFFFF);
@@ -511,6 +514,7 @@ static void _timer_callback(void)
     now = reference;
 #if (XTIMER_HZ < 1000000ul) && (STIMER_HZ >= 1000000ul)
     prev_x = now;
+    xtimer_sync = true;
 #endif
 
 overflow:
@@ -570,6 +574,7 @@ static void _timer_callback(void)
         now = _xtimer_lltimer_now();
 #if (XTIMER_HZ < 1000000ul) && (STIMER_HZ >= 1000000ul)
         prev_x = now;
+        xtimer_sync = true;
 #endif
         goto overflow;
     }
@@ -586,6 +591,7 @@ static void _timer_callback(void)
             now = _xtimer_lltimer_now();
 #if (XTIMER_HZ < 1000000ul) && (STIMER_HZ >= 1000000ul)
             prev_x = now;
+            xtimer_sync = true;
 #endif
             goto overflow;
         }
@@ -614,6 +620,7 @@ static void _timer_callback(void)
             now = _xtimer_lltimer_now();
 #if (XTIMER_HZ < 1000000ul) && (STIMER_HZ >= 1000000ul)
             prev_x = now;
+            xtimer_sync = true;
 #endif
             goto overflow;
         }
@@ -630,6 +637,7 @@ static void _timer_callback(void)
                 now = _xtimer_lltimer_now();
 #if (XTIMER_HZ < 1000000ul) && (STIMER_HZ >= 1000000ul)
                 prev_x = now;
+                xtimer_sync = true;
 #endif
                 goto overflow;
             }