ztimer/convert: pass-thru start/stop ops to lower timer

sys/include/ztimer/convert.h

@@ -71,6 +71,24 @@ void ztimer_convert_init(ztimer_convert_t *ztimer_convert,
  */
 void ztimer_convert_cancel(ztimer_clock_t *clock);
 
+/**
+ * @brief   ztimer_convert common start() op
+ *
+ * Used by some conversion modules as ztimer_clock_t::ops.start().
+ *
+ * @param[in]       clock   ztimer clock to operate on
+ */
+void ztimer_convert_start(ztimer_clock_t *clock);
+
+/**
+ * @brief   ztimer_convert common stop() op
+ *
+ * Used by some conversion modules as ztimer_clock_t::ops.stop().
+ *
+ * @param[in]       clock   ztimer clock to operate on
+ */
+void ztimer_convert_stop(ztimer_clock_t *clock);
+
 #ifdef __cplusplus
 }
 #endif

sys/ztimer/convert.c

@@ -35,6 +35,20 @@ void ztimer_convert_cancel(ztimer_clock_t *clock)
     ztimer_remove(ztimer_convert->lower, &ztimer_convert->lower_entry);
 }
 
+void ztimer_convert_start(ztimer_clock_t *clock)
+{
+    ztimer_convert_t *ztimer_convert = (ztimer_convert_t *)clock;
+
+    ztimer_acquire(ztimer_convert->lower);
+}
+
+void ztimer_convert_stop(ztimer_clock_t *clock)
+{
+    ztimer_convert_t *ztimer_convert = (ztimer_convert_t *)clock;
+
+    ztimer_release(ztimer_convert->lower);
+}
+
 void ztimer_convert_init(ztimer_convert_t *ztimer_convert,
                          ztimer_clock_t *lower,
                          uint32_t max_value)

sys/ztimer/convert_frac.c

@@ -74,6 +74,10 @@ static const ztimer_ops_t ztimer_convert_frac_ops = {
     .set = ztimer_convert_frac_op_set,
     .now = ztimer_convert_frac_op_now,
     .cancel = ztimer_convert_cancel,
+#if MODULE_ZTIMER_ONDEMAND
+    .start = ztimer_convert_start,
+    .stop = ztimer_convert_stop,
+#endif
 };
 
 static void ztimer_convert_frac_compute_scale(ztimer_convert_frac_t *self,

sys/ztimer/convert_muldiv64.c

@@ -98,6 +98,10 @@ static const ztimer_ops_t _ztimer_convert_muldiv64_ops = {
     .set = _ztimer_convert_muldiv64_set,
     .now = _ztimer_convert_muldiv64_now,
     .cancel = ztimer_convert_cancel,
+#if MODULE_ZTIMER_ONDEMAND
+    .start = ztimer_convert_start,
+    .stop = ztimer_convert_stop,
+#endif
 };
 
 void ztimer_convert_muldiv64_init(

sys/ztimer/convert_shift.c

@@ -78,6 +78,10 @@ static const ztimer_ops_t _ztimer_convert_shift_ops_up = {
     .set = _ztimer_convert_shift_up_set,
     .now = _ztimer_convert_shift_up_now,
     .cancel = ztimer_convert_cancel,
+#if MODULE_ZTIMER_ONDEMAND
+    .start = ztimer_convert_start,
+    .stop = ztimer_convert_stop,
+#endif
 };
 
 void ztimer_convert_shift_up_init(ztimer_convert_shift_t *clock,