diff --git a/demos/STM32/RT-STM32F746G-DISCOVERY/Makefile b/demos/STM32/RT-STM32F746G-DISCOVERY/Makefile
index 40b040625..94853d1b3 100644
--- a/demos/STM32/RT-STM32F746G-DISCOVERY/Makefile
+++ b/demos/STM32/RT-STM32F746G-DISCOVERY/Makefile
@@ -5,7 +5,7 @@
 
 # Compiler options here.
 ifeq ($(USE_OPT),)
-  USE_OPT = -O2 -ggdb -fomit-frame-pointer -falign-functions=16
+  USE_OPT = -O0 -ggdb -fomit-frame-pointer -falign-functions=16
 endif
 
 # C specific options here (added to USE_OPT).
diff --git a/demos/STM32/RT-STM32F746G-DISCOVERY/chconf.h b/demos/STM32/RT-STM32F746G-DISCOVERY/chconf.h
index 1bda70597..206f1d11d 100644
--- a/demos/STM32/RT-STM32F746G-DISCOVERY/chconf.h
+++ b/demos/STM32/RT-STM32F746G-DISCOVERY/chconf.h
@@ -49,7 +49,7 @@
  * @details Frequency of the system timer that drives the system ticks. This
  *          setting also defines the system tick time unit.
  */
-#define CH_CFG_ST_FREQUENCY                 10000
+#define CH_CFG_ST_FREQUENCY                 100000
 
 /**
  * @brief   Time intervals data size.
diff --git a/os/rt/include/chvt.h b/os/rt/include/chvt.h
index 3dc67f2a3..ea4493df3 100644
--- a/os/rt/include/chvt.h
+++ b/os/rt/include/chvt.h
@@ -395,19 +395,26 @@ static inline void chVTDoTickI(void) {
   systime_t now;
   sysinterval_t delta;
 
-  /* First timer to be processed.*/
+  /* Looping through timers.*/
   vtp = ch.vtlist.next;
-  now = chVTGetSystemTimeX();
-
-  /* All timers within the time window are triggered and removed,
-     note that the loop is stopped by the timers header having
-     "ch.vtlist.vt_delta == (sysinterval_t)-1" which is greater than
-     all deltas.*/
-  while (vtp->delta <= chTimeDiffX(ch.vtlist.lasttime, now)) {
+  while (true) {
     vtfunc_t fn;
 
+    /* The loop is stopped by the timers header having
+       "ch.vtlist.vt_delta == (sysinterval_t)-1" which
+       is greater than all deltas.*/
+    now = chVTGetSystemTimeX();
+    if (vtp->delta > chTimeDiffX(ch.vtlist.lasttime, now)) {
+      break;
+    }
+
+#if 0
     /* The "last time" becomes this timer's expiration time.*/
     ch.vtlist.lasttime = chTimeAddX(ch.vtlist.lasttime, vtp->delta);
+#else
+    /* The "last time" is set to the current time.*/
+    ch.vtlist.lasttime = now;
+#endif
 
     vtp->next->prev = (virtual_timer_t *)&ch.vtlist;
     ch.vtlist.next = vtp->next;
@@ -431,10 +438,8 @@ static inline void chVTDoTickI(void) {
        of the list.*/
     chSysLockFromISR();
 
-    /* Next element in the list, the current time could have advanced so
-       recalculating the time window.*/
+    /* Next element in the list.*/
     vtp = ch.vtlist.next;
-    now = chVTGetSystemTimeX();
   }
 
   /* if the list is empty, nothing else to do.*/
diff --git a/os/rt/src/chvt.c b/os/rt/src/chvt.c
index 1c5b2fea2..0667bf7c3 100644
--- a/os/rt/src/chvt.c
+++ b/os/rt/src/chvt.c
@@ -125,6 +125,13 @@ void chVTDoSetI(virtual_timer_t *vtp, sysinterval_t delay,
       vtp->prev = (virtual_timer_t *)&ch.vtlist;
       vtp->delta = delay;
 
+#if CH_CFG_INTERVALS_SIZE > CH_CFG_ST_RESOLUTION
+      /* The delta could be too large for the physical timer to handle.*/
+      if (delay > (sysinterval_t)TIME_MAX_SYSTIME) {
+        delay = (sysinterval_t)TIME_MAX_SYSTIME;
+      }
+#endif
+
       /* Being the first element in the list the alarm timer is started.*/
       port_timer_start_alarm(chTimeAddX(ch.vtlist.lasttime, delay));