diff --git a/boards/OLIMEX_LPC_P2148/buzzer.c b/boards/OLIMEX_LPC_P2148/buzzer.c
index 39c501e07..8f1137446 100644
--- a/boards/OLIMEX_LPC_P2148/buzzer.c
+++ b/boards/OLIMEX_LPC_P2148/buzzer.c
@@ -69,7 +69,9 @@ void buzzInit(void) {
 static void stop(void *p) {
 
   StopCounter((TC *)p);
+  chSysLockFromIsr();
   chEvtBroadcastI(&BuzzerSilentEventSource);
+  chSysUnlockFromIsr();
 }
 
 /**
diff --git a/demos/ARMCM3-STM32F103ZG-FATFS/main.c b/demos/ARMCM3-STM32F103ZG-FATFS/main.c
index 4181c7004..8199275cd 100644
--- a/demos/ARMCM3-STM32F103ZG-FATFS/main.c
+++ b/demos/ARMCM3-STM32F103ZG-FATFS/main.c
@@ -89,6 +89,7 @@ bool_t sdc_lld_is_write_protected(SDCDriver *sdcp) {
 static void tmrfunc(void *p) {
   SDCDriver *sdcp = p;
 
+  chSysLockFromIsr();
   if (cnt > 0) {
     if (sdcIsCardInserted(sdcp)) {
       if (--cnt == 0) {
@@ -105,6 +106,7 @@ static void tmrfunc(void *p) {
     }
   }
   chVTSetI(&tmr, MS2ST(SDC_POLLING_DELAY), tmrfunc, sdcp);
+  chSysUnlockFromIsr();
 }
 
 /**
diff --git a/docs/reports/SPC563M64-80.txt b/docs/reports/SPC563M64-80.txt
index d786aa30e..fc754adcc 100644
--- a/docs/reports/SPC563M64-80.txt
+++ b/docs/reports/SPC563M64-80.txt
@@ -5,8 +5,8 @@ Settings: SYSCLK=80
 
 *** ChibiOS/RT test suite
 ***
-*** Kernel:       2.4.0
-*** Compiled:     Jan 17 2012 - 14:35:40
+*** Kernel:       2.5.0
+*** Compiled:     Feb  8 2012 - 10:21:46
 *** Compiler:     GCC 4.4.1
 *** Architecture: Power Architecture
 *** Core Variant: e200z3
@@ -100,35 +100,35 @@ Settings: SYSCLK=80
 --- Result: SUCCESS
 ----------------------------------------------------------------------------
 --- Test Case 11.1 (Benchmark, messages #1)
---- Score : 283160 msgs/S, 566320 ctxswc/S
+--- Score : 278226 msgs/S, 556452 ctxswc/S
 --- Result: SUCCESS
 ----------------------------------------------------------------------------
 --- Test Case 11.2 (Benchmark, messages #2)
---- Score : 226208 msgs/S, 452416 ctxswc/S
+--- Score : 224935 msgs/S, 449870 ctxswc/S
 --- Result: SUCCESS
 ----------------------------------------------------------------------------
 --- Test Case 11.3 (Benchmark, messages #3)
---- Score : 226208 msgs/S, 452416 ctxswc/S
+--- Score : 224935 msgs/S, 449870 ctxswc/S
 --- Result: SUCCESS
 ----------------------------------------------------------------------------
 --- Test Case 11.4 (Benchmark, context switch)
---- Score : 897232 ctxswc/S
+--- Score : 890960 ctxswc/S
 --- Result: SUCCESS
 ----------------------------------------------------------------------------
 --- Test Case 11.5 (Benchmark, threads, full cycle)
---- Score : 180251 threads/S
+--- Score : 178638 threads/S
 --- Result: SUCCESS
 ----------------------------------------------------------------------------
 --- Test Case 11.6 (Benchmark, threads, create only)
---- Score : 261812 threads/S
+--- Score : 255935 threads/S
 --- Result: SUCCESS
 ----------------------------------------------------------------------------
 --- Test Case 11.7 (Benchmark, mass reschedule, 5 threads)
---- Score : 73862 reschedules/S, 443172 ctxswc/S
+--- Score : 73319 reschedules/S, 439914 ctxswc/S
 --- Result: SUCCESS
 ----------------------------------------------------------------------------
 --- Test Case 11.8 (Benchmark, round robin context switching)
---- Score : 614140 ctxswc/S
+--- Score : 609448 ctxswc/S
 --- Result: SUCCESS
 ----------------------------------------------------------------------------
 --- Test Case 11.9 (Benchmark, I/O Queues throughput)
@@ -136,7 +136,7 @@ Settings: SYSCLK=80
 --- Result: SUCCESS
 ----------------------------------------------------------------------------
 --- Test Case 11.10 (Benchmark, virtual timers set/reset)
---- Score : 1093664 timers/S
+--- Score : 1094200 timers/S
 --- Result: SUCCESS
 ----------------------------------------------------------------------------
 --- Test Case 11.11 (Benchmark, semaphores wait/signal)
@@ -144,11 +144,11 @@ Settings: SYSCLK=80
 --- Result: SUCCESS
 ----------------------------------------------------------------------------
 --- Test Case 11.12 (Benchmark, mutexes lock/unlock)
---- Score : 841236 lock+unlock/S
+--- Score : 841232 lock+unlock/S
 --- Result: SUCCESS
 ----------------------------------------------------------------------------
 --- Test Case 11.13 (Benchmark, RAM footprint)
---- System: 768 bytes
+--- System: 764 bytes
 --- Thread: 72 bytes
 --- Timer : 20 bytes
 --- Semaph: 12 bytes
diff --git a/os/hal/platforms/STM32/i2c_lld.c b/os/hal/platforms/STM32/i2c_lld.c
index 996033da5..7458d9252 100644
--- a/os/hal/platforms/STM32/i2c_lld.c
+++ b/os/hal/platforms/STM32/i2c_lld.c
@@ -167,8 +167,10 @@ static void i2c_lld_safety_timeout(void *p) {
 
   if (i2cp->thread) {
     i2c_lld_abort_operation(i2cp);
+    chSysLockFromIsr();
     i2cp->thread->p_u.rdymsg = RDY_TIMEOUT;
     chSchReadyI(i2cp->thread);
+    chSysUnlockFromIsr();
   }
 }
 
diff --git a/os/hal/src/mmc_spi.c b/os/hal/src/mmc_spi.c
index 8f11355b8..f4bcb51fd 100644
--- a/os/hal/src/mmc_spi.c
+++ b/os/hal/src/mmc_spi.c
@@ -105,6 +105,7 @@ static uint8_t crc7(uint8_t crc, const uint8_t *buffer, size_t len) {
 static void tmrfunc(void *p) {
   MMCDriver *mmcp = p;
 
+  chSysLockFromIsr();
   if (mmcp->cnt > 0) {
     if (mmcp->is_inserted()) {
       if (--mmcp->cnt == 0) {
@@ -123,6 +124,7 @@ static void tmrfunc(void *p) {
     }
   }
   chVTSetI(&mmcp->vt, MS2ST(MMC_POLLING_DELAY), tmrfunc, mmcp);
+  chSysUnlockFromIsr();
 }
 
 /**
diff --git a/os/kernel/include/chvt.h b/os/kernel/include/chvt.h
index 95fb16408..355f66064 100644
--- a/os/kernel/include/chvt.h
+++ b/os/kernel/include/chvt.h
@@ -55,7 +55,8 @@
  *
  * @api
  */
-#define MS2ST(msec) ((systime_t)(((((msec) - 1L) * CH_FREQUENCY) / 1000L) + 1L))
+#define MS2ST(msec) ((systime_t)(((((msec) - 1L) * CH_FREQUENCY) /          \
+                                   1000L) + 1L))
 
 /**
  * @brief   Microseconds to system ticks.
@@ -67,7 +68,8 @@
  *
  * @api
  */
-#define US2ST(usec) ((systime_t)(((((usec) - 1L) * CH_FREQUENCY) / 1000000L) + 1L))
+#define US2ST(usec) ((systime_t)(((((usec) - 1L) * CH_FREQUENCY) /          \
+                                  1000000L) + 1L))
 /** @} */
 
 /**
@@ -112,40 +114,84 @@ typedef struct {
   volatile systime_t    vt_systime; /**< @brief System Time counter.        */
 } VTList;
 
-extern VTList vtlist;
-
 /**
  * @name    Macro Functions
  * @{
  */
 /**
  * @brief   Virtual timers ticker.
+ * @note    The system lock is released before entering the callback and
+ *          re-acquired immediately after. It is callback's responsibility
+ *          to acquire the lock if needed. This is done in order to reduce
+ *          interrupts jitter when many timers are in use.
  *
  * @iclass
  */
-#define chVTDoTickI() {                                                 \
-  vtlist.vt_systime++;                                                  \
-  if (&vtlist != (VTList *)vtlist.vt_next) {                            \
-    VirtualTimer *vtp;                                                  \
-                                                                        \
-    --vtlist.vt_next->vt_time;                                          \
-    while (!(vtp = vtlist.vt_next)->vt_time) {                          \
-      vtfunc_t fn = vtp->vt_func;                                       \
-      vtp->vt_func = (vtfunc_t)NULL;                                    \
-      vtp->vt_next->vt_prev = (void *)&vtlist;                          \
-      (&vtlist)->vt_next = vtp->vt_next;                                \
-      fn(vtp->vt_par);                                                  \
-    }                                                                   \
-  }                                                                     \
+#define chVTDoTickI() {                                                     \
+  vtlist.vt_systime++;                                                      \
+  if (&vtlist != (VTList *)vtlist.vt_next) {                                \
+    VirtualTimer *vtp;                                                      \
+                                                                            \
+    --vtlist.vt_next->vt_time;                                              \
+    while (!(vtp = vtlist.vt_next)->vt_time) {                              \
+      vtfunc_t fn = vtp->vt_func;                                           \
+      vtp->vt_func = (vtfunc_t)NULL;                                        \
+      vtp->vt_next->vt_prev = (void *)&vtlist;                              \
+      (&vtlist)->vt_next = vtp->vt_next;                                    \
+      chSysUnlockFromIsr();                                                 \
+      fn(vtp->vt_par);                                                      \
+      chSysLockFromIsr();                                                   \
+    }                                                                       \
+  }                                                                         \
 }
 
 /**
- * @brief   Returns TRUE if the speciified timer is armed.
+ * @brief   Returns @p TRUE if the specified timer is armed.
  *
  * @iclass
  */
 #define chVTIsArmedI(vtp) ((vtp)->vt_func != NULL)
 
+/**
+ * @brief   Enables a virtual timer.
+ * @note    The associated function is invoked from interrupt context.
+ *
+ * @param[out] vtp      the @p VirtualTimer structure pointer
+ * @param[in] time      the number of ticks before the operation timeouts, the
+ *                      special values are handled as follow:
+ *                      - @a TIME_INFINITE is allowed but interpreted as a
+ *                        normal time specification.
+ *                      - @a TIME_IMMEDIATE this value is not allowed.
+ *                      .
+ * @param[in] vtfunc    the timer callback function. After invoking the
+ *                      callback the timer is disabled and the structure can
+ *                      be disposed or reused.
+ * @param[in] par       a parameter that will be passed to the callback
+ *                      function
+ *
+ * @api
+ */
+#define chVTSet(vtp, time, vtfunc, par) {                                   \
+  chSysLock();                                                              \
+  chVTSetI(vtp, time, vtfunc, par);                                         \
+  chSysUnlock();                                                            \
+}
+
+/**
+ * @brief   Disables a Virtual Timer.
+ * @note    The timer is first checked and disabled only if armed.
+ *
+ * @param[in] vtp       the @p VirtualTimer structure pointer
+ *
+ * @api
+ */
+#define chVTReset(vtp) {                                                    \
+  chSysLock();                                                              \
+  if (chVTIsArmedI(vtp))                                                    \
+    chVTResetI(vtp);                                                        \
+  chSysUnlock();                                                            \
+}
+
 /**
  * @brief   Current system time.
  * @details Returns the number of system ticks since the @p chSysInit()
@@ -153,13 +199,15 @@ extern VTList vtlist;
  * @note    The counter can reach its maximum and then restart from zero.
  * @note    This function is designed to work with the @p chThdSleepUntil().
  *
- * @return              The system time in ticks.r
+ * @return              The system time in ticks.
  *
  * @api
  */
 #define chTimeNow() (vtlist.vt_systime)
 /** @} */
 
+extern VTList vtlist;
+
 /*
  * Virtual Timers APIs.
  */
diff --git a/os/kernel/src/chschd.c b/os/kernel/src/chschd.c
index 808e06300..9739a595b 100644
--- a/os/kernel/src/chschd.c
+++ b/os/kernel/src/chschd.c
@@ -127,10 +127,12 @@ void chSchGoSleepS(tstate_t newstate) {
 static void wakeup(void *p) {
   Thread *tp = (Thread *)p;
 
+  chSysLockFromIsr();
   switch (tp->p_state) {
   case THD_STATE_READY:
     /* Handling the special case where the thread has been made ready by
        another thread with higher priority.*/
+    chSysUnlockFromIsr();
     return;
 #if CH_USE_SEMAPHORES || CH_USE_QUEUES ||                                   \
     (CH_USE_CONDVARS && CH_USE_CONDVARS_TIMEOUT)
@@ -151,6 +153,7 @@ static void wakeup(void *p) {
   }
   tp->p_u.rdymsg = RDY_TIMEOUT;
   chSchReadyI(tp);
+  chSysUnlockFromIsr();
 }
 
 /**
diff --git a/os/kernel/src/chvt.c b/os/kernel/src/chvt.c
index 4869cebef..6389aaf6d 100644
--- a/os/kernel/src/chvt.c
+++ b/os/kernel/src/chvt.c
@@ -49,8 +49,7 @@ void _vt_init(void) {
 
 /**
  * @brief   Enables a virtual timer.
- * @note    The associated function is invoked by an interrupt handler within
- *          the I-Locked state, see @ref system_states.
+ * @note    The associated function is invoked from interrupt context.
  *
  * @param[out] vtp      the @p VirtualTimer structure pointer
  * @param[in] time      the number of ticks before the operation timeouts, the
diff --git a/os/various/evtimer.c b/os/various/evtimer.c
index 314e0cc12..fedc5d6e4 100644
--- a/os/various/evtimer.c
+++ b/os/various/evtimer.c
@@ -32,8 +32,10 @@
 static void tmrcb(void *p) {
   EvTimer *etp = p;
 
+  chSysLockFromIsr();
   chEvtBroadcastI(&etp->et_es);
   chVTSetI(&etp->et_vt, etp->et_interval, tmrcb, etp);
+  chSysUnlockFromIsr();
 }
 
 /**
@@ -60,12 +62,7 @@ void evtStart(EvTimer *etp) {
  */
 void evtStop(EvTimer *etp) {
 
-  chSysLock();
-
-  if (chVTIsArmedI(&etp->et_vt))
-    chVTResetI(&etp->et_vt);
-
-  chSysUnlock();
+  chVTReset(&etp->et_vt);
 }
 
 /** @} */
diff --git a/readme.txt b/readme.txt
index c4ac352a4..d757e889c 100644
--- a/readme.txt
+++ b/readme.txt
@@ -93,6 +93,9 @@
 - NEW: Revision of the round-robin scheduling, now threads do not lose their
   time slice when preempted. Each thread has its own time slices counter.
   TODO: Seek optimizations.
+- NEW: Modified the Virtual Timers management, now the callback is invoked
+  not in lock mode. This change reduces the interrupt jitter caused by
+  multiple timers used at same time.
 
 *** 2.3.5 ***
 - FIX: Fixed RTC compile problem on STM32F103 (bug 3468445).
diff --git a/test/test.c b/test/test.c
index bce0b5788..55cfdf445 100644
--- a/test/test.c
+++ b/test/test.c
@@ -278,9 +278,7 @@ void test_start_timer(unsigned ms) {
 
   systime_t duration = MS2ST(ms);
   test_timer_done = FALSE;
-  chSysLock();
-  chVTSetI(&vt, duration, tmr, NULL);
-  chSysUnlock();
+  chVTSet(&vt, duration, tmr, NULL);
 }
 
 /*
diff --git a/testhal/STM32F1xx/UART/main.c b/testhal/STM32F1xx/UART/main.c
index bdc222e35..0d36e2b89 100644
--- a/testhal/STM32F1xx/UART/main.c
+++ b/testhal/STM32F1xx/UART/main.c
@@ -26,7 +26,10 @@ static VirtualTimer vt1, vt2;
 static void restart(void *p) {
 
   (void)p;
+
+  chSysLockFromIsr();
   uartStartSendI(&UARTD2, 14, "Hello World!\r\n");
+  chSysUnlockFromIsr();
 }
 
 static void ledoff(void *p) {
diff --git a/testhal/STM32F4xx/UART/main.c b/testhal/STM32F4xx/UART/main.c
index 377a75934..69aed3c19 100644
--- a/testhal/STM32F4xx/UART/main.c
+++ b/testhal/STM32F4xx/UART/main.c
@@ -26,7 +26,10 @@ static VirtualTimer vt1, vt2;
 static void restart(void *p) {
 
   (void)p;
+
+  chSysLockFromIsr();
   uartStartSendI(&UARTD2, 14, "Hello World!\r\n");
+  chSysUnlockFromIsr();
 }
 
 static void ledoff(void *p) {
diff --git a/testhal/STM32L1xx/UART/main.c b/testhal/STM32L1xx/UART/main.c
index 8bb5ea6d7..65f834672 100644
--- a/testhal/STM32L1xx/UART/main.c
+++ b/testhal/STM32L1xx/UART/main.c
@@ -26,7 +26,10 @@ static VirtualTimer vt1, vt2;
 static void restart(void *p) {
 
   (void)p;
+
+  chSysLockFromIsr();
   uartStartSendI(&UARTD1, 14, "Hello World!\r\n");
+  chSysUnlockFromIsr();
 }
 
 static void ledoff(void *p) {
diff --git a/todo.txt b/todo.txt
index 04ca10f0b..32c58b9b2 100644
--- a/todo.txt
+++ b/todo.txt
@@ -13,8 +13,8 @@ X SDC driver port to STM32F2 and STM32F4.
 
 Within 2.5.x:
 * Revision of scheduling strategy for threads at equal priority.
-- Handling of Virtual Timer callbacks out of critical zone.
-- Add normal API (not iclass) variants of the VT functions.
+* Handling of Virtual Timer callbacks out of critical zone.
+* Add normal API (not iclass) variants of the VT functions.
 - Add the RTC service inside the kernel and port, remove from HAL.
 - Add option to use the RTC counter instead of the systick counter into the
   trace buffer.