From 2b53f35a28b791d945a0d2e170e1dd0a3483b81f Mon Sep 17 00:00:00 2001
From: Jue <me@jue.yt>
Date: Thu, 3 Nov 2022 14:25:04 +0100
Subject: [PATCH] ztimer: warn users when calling ztimer_now() on inactive
 clocks

---
 sys/include/ztimer.h | 16 ++++++++++++++--
 sys/ztimer/core.c    | 15 +++++++++++++++
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/sys/include/ztimer.h b/sys/include/ztimer.h
index f6ee9c8c7e..3ee7356463 100644
--- a/sys/include/ztimer.h
+++ b/sys/include/ztimer.h
@@ -554,6 +554,17 @@ int ztimer_msg_receive_timeout(ztimer_clock_t *clock, msg_t *msg,
  */
 ztimer_now_t _ztimer_now_extend(ztimer_clock_t *clock);
 
+/**
+ * @brief asserts the given clock to be active
+ *
+ * @internal
+ *
+ * @note  This function is internal
+ *
+ * @param[in]   clock          ztimer clock to operate on
+ */
+void _ztimer_assert_clock_active(ztimer_clock_t *clock);
+
 /**
  * @brief   Get the current time from a clock
  *
@@ -668,9 +679,10 @@ ztimer_now_t _ztimer_now_extend(ztimer_clock_t *clock);
  */
 static inline ztimer_now_t ztimer_now(ztimer_clock_t *clock)
 {
-#if MODULE_ZTIMER_ONDEMAND_STRICT
-    assert(clock->users > 0);
+#if MODULE_ZTIMER_ONDEMAND && DEVELHELP
+    _ztimer_assert_clock_active(clock);
 #endif
+
 #if MODULE_ZTIMER_NOW64
     if (1) {
 #elif MODULE_ZTIMER_EXTEND
diff --git a/sys/ztimer/core.c b/sys/ztimer/core.c
index f8c4e3f9e9..e3f9ab0ff3 100644
--- a/sys/ztimer/core.c
+++ b/sys/ztimer/core.c
@@ -32,6 +32,7 @@
 #include "pm_layered.h"
 #endif
 #include "ztimer.h"
+#include "log.h"
 
 #define ENABLE_DEBUG 0
 #include "debug.h"
@@ -529,3 +530,17 @@ static void _ztimer_print(const ztimer_clock_t *clock)
     } while ((entry = entry->next));
     puts("");
 }
+
+#if MODULE_ZTIMER_ONDEMAND && DEVELHELP
+void _ztimer_assert_clock_active(ztimer_clock_t *clock)
+{
+    if (clock->users == 0) {
+        LOG_WARNING("WARNING! You are accessing ztimer_now() on a non-active clock!\n"
+                    "         Make sure to call ztimer_acquire() before accessing ztimer_now().\n"
+                    "         Once you've finished don't forget to call ztimer_release().\n");
+    }
+#if MODULE_ZTIMER_ONDEMAND_STRICT
+    assert(clock->users > 0);
+#endif
+}
+#endif