From b8d8159f9f9ba371b83acddf989c516cc5d7f0de Mon Sep 17 00:00:00 2001
From: Juergen Fitschen <me@jue.yt>
Date: Thu, 19 Mar 2020 18:50:43 +0100
Subject: [PATCH] sys/evtimer: introduce ZTIMER_MSEC as timer backend

---
 Makefile.dep            |  4 +++-
 sys/evtimer/evtimer.c   | 44 ++++++++++++++++++++++++++++++++++-------
 sys/include/evtimer.h   |  9 +++++++++
 sys/ztimer/Makefile.dep |  8 +++++++-
 4 files changed, 56 insertions(+), 9 deletions(-)

diff --git a/Makefile.dep b/Makefile.dep
index 867d4615acf76..798dcb05ee102 100644
--- a/Makefile.dep
+++ b/Makefile.dep
@@ -687,7 +687,9 @@ ifneq (,$(filter phydat,$(USEMODULE)))
 endif
 
 ifneq (,$(filter evtimer,$(USEMODULE)))
-  USEMODULE += xtimer
+  ifeq (,$(filter evtimer_on_ztimer,$(USEMODULE)))
+    USEMODULE += xtimer
+  endif
 endif
 
 ifneq (,$(filter can_linux,$(USEMODULE)))
diff --git a/sys/evtimer/evtimer.c b/sys/evtimer/evtimer.c
index aabff9fafc63e..8e6743291eeb6 100644
--- a/sys/evtimer/evtimer.c
+++ b/sys/evtimer/evtimer.c
@@ -24,7 +24,6 @@
 
 #include "div.h"
 #include "irq.h"
-#include "xtimer.h"
 
 #include "evtimer.h"
 
@@ -91,27 +90,57 @@ static void _del_event_from_list(evtimer_t *evtimer, evtimer_event_t *event)
     }
 }
 
-static void _set_timer(xtimer_t *timer, uint32_t offset_ms)
+static void _set_timer(evtimer_t *evtimer)
 {
-    uint64_t offset_us = (uint64_t)offset_ms * US_PER_MS;
+    evtimer_event_t *next_event = evtimer->events;
+
+#ifdef MODULE_EVTIMER_ON_ZTIMER
+    evtimer->base = ztimer_now(ZTIMER_MSEC);
+
+    DEBUG("evtimer: now=%" PRIu32 " ms setting ztimer to %" PRIu32 " ms\n",
+          evtimer->base, next_event->offset);
+
+    ztimer_set(ZTIMER_MSEC, &evtimer->timer, next_event->offset);
+#else /* ifdef MODULE_EVTIMER_ON_ZTIMER */
+    uint64_t offset_us = (uint64_t)next_event->offset * US_PER_MS;
 
     DEBUG("evtimer: now=%" PRIu32 " us setting xtimer to %" PRIu32 ":%" PRIu32 " us\n",
           xtimer_now_usec(), (uint32_t)(offset_us >> 32), (uint32_t)(offset_us));
 
-    xtimer_set64(timer, offset_us);
+    xtimer_set64(&evtimer->timer, offset_us);
+#endif /* ifndef MODULE_EVTIMER_ON_ZTIMER */
 }
 
 static void _update_timer(evtimer_t *evtimer)
 {
     if (evtimer->events) {
-        evtimer_event_t *event = evtimer->events;
-        _set_timer(&evtimer->timer, event->offset);
+        _set_timer(evtimer);
     }
     else {
+#ifdef MODULE_EVTIMER_ON_ZTIMER
+        ztimer_remove(ZTIMER_MSEC, &evtimer->timer);
+#else
         xtimer_remove(&evtimer->timer);
+#endif
     }
 }
 
+#ifdef MODULE_EVTIMER_ON_ZTIMER
+static void _update_head_offset(evtimer_t *evtimer)
+{
+    if (evtimer->events) {
+        evtimer_event_t *event = evtimer->events;
+        uint32_t now = ztimer_now(ZTIMER_MSEC);
+        uint32_t elapsed = now - evtimer->base;
+        if (elapsed > event->offset) {
+            event->offset = 0;
+        } else {
+            event->offset -= elapsed;
+        }
+        evtimer->base = now;
+    }
+}
+#else /* ifdef MODULE_EVTIMER_ON_ZTIMER */
 static uint32_t _get_offset(xtimer_t *timer)
 {
     uint64_t now_us = xtimer_now_usec64();
@@ -138,6 +167,7 @@ static void _update_head_offset(evtimer_t *evtimer)
         DEBUG("evtimer: _update_head_offset(): new head offset %" PRIu32 "\n", event->offset);
     }
 }
+#endif /* ifndef MODULE_EVTIMER_ON_ZTIMER */
 
 void evtimer_add(evtimer_t *evtimer, evtimer_event_t *event)
 {
@@ -148,7 +178,7 @@ void evtimer_add(evtimer_t *evtimer, evtimer_event_t *event)
     _update_head_offset(evtimer);
     _add_event_to_list(evtimer, event);
     if (evtimer->events == event) {
-        _set_timer(&evtimer->timer, event->offset);
+        _set_timer(evtimer);
     }
     irq_restore(state);
     if (sched_context_switch_request) {
diff --git a/sys/include/evtimer.h b/sys/include/evtimer.h
index da8dc9a1efca7..48bb1f2345754 100644
--- a/sys/include/evtimer.h
+++ b/sys/include/evtimer.h
@@ -45,7 +45,11 @@
 
 #include <stdint.h>
 
+#ifdef MODULE_EVTIMER_ON_ZTIMER
+#include "ztimer.h"
+#else
 #include "xtimer.h"
+#endif
 
 #ifdef __cplusplus
 extern "C" {
@@ -68,7 +72,12 @@ typedef void(*evtimer_callback_t)(evtimer_event_t* event);
  * @brief   Event timer
  */
 typedef struct {
+#ifdef MODULE_EVTIMER_ON_ZTIMER
+    ztimer_t timer;                 /**< Timer */
+    uint32_t base;                  /**< Aboslut time the first event is built on */
+#else
     xtimer_t timer;                 /**< Timer */
+#endif
     evtimer_callback_t callback;    /**< Handler function for this evtimer's
                                          event type */
     evtimer_event_t *events;        /**< Event queue */
diff --git a/sys/ztimer/Makefile.dep b/sys/ztimer/Makefile.dep
index 1ccc74b29831a..6aff1c84c223c 100644
--- a/sys/ztimer/Makefile.dep
+++ b/sys/ztimer/Makefile.dep
@@ -27,7 +27,7 @@ endif
 ifneq (,$(filter ztimer,$(USEMODULE)))
   ifneq  (,$(filter xtimer,$(USEMODULE)))
     ifeq (,$(filter ztimer_xtimer_compat,$(USEMODULE)))
-        USEMODULE += xtimer_on_ztimer
+      USEMODULE += xtimer_on_ztimer
     endif
   endif
 endif
@@ -38,6 +38,12 @@ ifneq (,$(filter xtimer_on_ztimer,$(USEMODULE)))
   PSEUDOMODULES += xtimer_on_ztimer
 endif
 
+# make evtimer use ztimer_msec as low level timer
+ifneq (,$(filter evtimer_on_ztimer,$(USEMODULE)))
+  USEMODULE += ztimer_msec
+  PSEUDOMODULES += evtimer_on_ztimer
+endif
+
 # "ztimer_xtimer_compat" is a wrapper of the xtimer API on ztimer_used
 # (it is currently incomplete). Unless doing testing, use "xtimer_on_ztimer".
 ifneq (,$(filter ztimer_xtimer_compat,$(USEMODULE)))