diff --git a/os/hal/platforms/STM32/RTCv1/rtc_lld.c b/os/hal/platforms/STM32/RTCv1/rtc_lld.c
index 478b16f39..b90b1e668 100644
--- a/os/hal/platforms/STM32/RTCv1/rtc_lld.c
+++ b/os/hal/platforms/STM32/RTCv1/rtc_lld.c
@@ -53,71 +53,44 @@ RTCDriver RTCD1;
 /*===========================================================================*/
 
 /**
- * @brief   Shared IRQ handler.
- *
- * @param[in] rtcp    pointer to a @p RTCDriver object
+ * @brief   Wait for synchronization of RTC registers with APB1 bus.
+ * @details This function must be invoked before trying to read RTC registers
+ *          in the backup domain: DIV, CNT, ALR. CR registers can always
+ *          be read.
  *
  * @notapi
  */
-static void rtc_lld_serve_interrupt(RTCDriver *rtcp) {
+static void rtc_lld_apb1_sync(void) {
 
-  PWR->CR |= PWR_CR_DBP;
-  chSysLockFromIsr();
-
-  if ((RTC->CRH & RTC_CRH_SECIE) && (RTC->CRL & RTC_CRL_SECF)) {
-    rtcp->callback(rtcp, RTC_EVENT_SECOND);
-    RTC->CRL &= ~RTC_CRL_SECF;
-  }
-  if ((RTC->CRH & RTC_CRH_ALRIE) && (RTC->CRL & RTC_CRL_ALRF)) {
-    rtcp->callback(rtcp, RTC_EVENT_ALARM);
-    RTC->CRL &= ~RTC_CRL_ALRF;
-  }
-  if ((RTC->CRH & RTC_CRH_OWIE) && (RTC->CRL & RTC_CRL_OWF)) {
-    rtcp->callback(rtcp, RTC_EVENT_OVERFLOW);
-    RTC->CRL &= ~RTC_CRL_OWF;
-  }
-
-  chSysUnlockFromIsr();
-  PWR->CR &= ~PWR_CR_DBP;
-}
-
-/**
- * @brief   Wait for synchronization of RTC registers.
- * @details Ensure that RTC_CNT and RTC_DIV contain actual values after
- *          enabling clocking on APB1, because these values only update
- *          when APB1 functioning.
- *
- * @notapi
- */
-static void rtc_lld_wait_sync(void) {
-  while (!(RTC->CRL & RTC_CRL_RSF))
+  while ((RTC->CRL & RTC_CRL_RSF) == 0)
     ;
 }
 
 /**
- * @brief   Acquire exclusive write access to RTC registers.
+ * @brief   Acquires write access to RTC registers.
+ * @details Before writing to the backup domain RTC registers the previous
+ *          write operation must be completed. Use this function before
+ *          writing to PRL, CNT, ALR registers. CR registers can always
+ *          be written.
  *
  * @notapi
  */
 static void rtc_lld_acquire(void) {
 
-  /* Waits registers write completion.*/
-BEGIN:
   while ((RTC->CRL & RTC_CRL_RTOFF) == 0)
     ;
-  chSysLock();
-  if ((RTC->CRL & RTC_CRL_RTOFF) == 0){
-    chSysUnlock();
-    goto BEGIN;
-  }
+  RTC->CRL |= RTC_CRL_CNF;
 }
 
 /**
- * @brief   Release exclusive write access to RTC registers.
+ * @brief   Releases write access to RTC registers.
  *
  * @notapi
  */
-#define rtc_lld_release() {chSysUnlock();}
+static void  rtc_lld_release(void) {
+
+  RTC->CRL &= ~RTC_CRL_CNF;
+}
 
 /*===========================================================================*/
 /* Driver interrupt handlers.                                                */
@@ -129,10 +102,22 @@ BEGIN:
  * @isr
  */
 CH_IRQ_HANDLER(RTC_IRQHandler) {
+  uint16_t flags;
 
   CH_IRQ_PROLOGUE();
 
-  rtc_lld_serve_interrupt(&RTCD1);
+  /* Mask of all enabled and pending sources.*/
+  flags = RTC->CRH & RTC->CRL;
+  RTC->CRL &= ~(RTC_CRL_SECF | RTC_CRL_ALRF | RTC_CRL_OWF);
+
+  if (flags & RTC_CRL_SECF)
+    RTCD1.callback(&RTCD1, RTC_EVENT_SECOND);
+
+  if (flags & RTC_CRL_ALRF)
+    RTCD1.callback(&RTCD1, RTC_EVENT_ALARM);
+
+  if (flags & RTC_CRL_OWF)
+    RTCD1.callback(&RTCD1, RTC_EVENT_OVERFLOW);
 
   CH_IRQ_EPILOGUE();
 }
@@ -151,36 +136,26 @@ CH_IRQ_HANDLER(RTC_IRQHandler) {
  */
 void rtc_lld_init(void){
 
-  PWR->CR |= PWR_CR_DBP;
+  /* Required because access to PRL.*/
+  rtc_lld_apb1_sync();
 
-  RTC->CRL &= ~(RTC_CRL_OWF | RTC_CRL_ALRF | RTC_CRL_SECF);
-  rtc_lld_wait_sync();
-
-  /* Write preload register only if its value is not equal to desired value.*/
+  /* Writes preload register only if its value is not equal to desired value.*/
   if (STM32_RTCCLK != (((uint32_t)(RTC->PRLH)) << 16) +
                        ((uint32_t)RTC->PRLL) + 1) {
-
-    /* Enters configuration mode and writes PRLx registers then leaves the
-       configuration mode.*/
     rtc_lld_acquire();
-    RTC->CRL |= RTC_CRL_CNF;
     RTC->PRLH = (uint16_t)((STM32_RTCCLK - 1) >> 16);
     RTC->PRLL = (uint16_t)((STM32_RTCCLK - 1) & 0xFFFF);
-    RTC->CRL &= ~RTC_CRL_CNF;
     rtc_lld_release();
   }
 
   /* All interrupts initially disabled.*/
-  if (RTC->CRH != 0){
-    rtc_lld_acquire();
-    RTC->CRH = 0;
-    rtc_lld_release();
-  }
-
-  PWR->CR &= ~PWR_CR_DBP;
+  RTC->CRH = 0;
 
   /* Callback initially disabled.*/
   RTCD1.callback = NULL;
+
+  /* IRQ vector permanently assigned to this driver.*/
+  nvicEnableVector(RTC_IRQn, CORTEX_PRIORITY_MASK(STM32_RTC_IRQ_PRIORITY));
 }
 
 /**
@@ -197,14 +172,10 @@ void rtc_lld_set_time(RTCDriver *rtcp, const RTCTime *timespec) {
 
   (void)rtcp;
 
-  PWR->CR |= PWR_CR_DBP;
   rtc_lld_acquire();
-  RTC->CRL |= RTC_CRL_CNF;
   RTC->CNTH = (uint16_t)(timespec->tv_sec >> 16);
   RTC->CNTL = (uint16_t)(timespec->tv_sec & 0xFFFF);
-  RTC->CRL &= ~RTC_CRL_CNF;
   rtc_lld_release();
-  PWR->CR &= ~PWR_CR_DBP;
 }
 
 /**
@@ -220,9 +191,10 @@ void rtc_lld_get_time(RTCDriver *rtcp, RTCTime *timespec) {
 
   uint32_t time_frac;
 
-  /* The read is repeated until we are able to do it twice and obtain the
-     same result.*/
-  rtc_lld_wait_sync();
+  /* Required because access to CNT and DIV.*/
+  rtc_lld_apb1_sync();
+
+  /* Loops until two consecutive read returning the same value.*/
   do {
     timespec->tv_sec = ((uint32_t)(RTC->CNTH) << 16) + RTC->CNTL;
     time_frac = (((uint32_t)RTC->DIVH) << 16) + (uint32_t)RTC->DIVL;
@@ -250,11 +222,7 @@ void rtc_lld_set_alarm(RTCDriver *rtcp,
   (void)rtcp;
   (void)alarm;
 
-  /* Enters configuration mode and writes ALRHx registers then leaves the
-     configuration mode.*/
-  PWR->CR |= PWR_CR_DBP;
   rtc_lld_acquire();
-  RTC->CRL |= RTC_CRL_CNF;
   if (alarmspec != NULL) {
     RTC->ALRH = (uint16_t)(alarmspec->tv_sec >> 16);
     RTC->ALRL = (uint16_t)(alarmspec->tv_sec & 0xFFFF);
@@ -263,9 +231,7 @@ void rtc_lld_set_alarm(RTCDriver *rtcp,
     RTC->ALRH = 0;
     RTC->ALRL = 0;
   }
-  RTC->CRL &= ~RTC_CRL_CNF;
   rtc_lld_release();
-  PWR->CR &= ~PWR_CR_DBP;
 }
 
 /**
@@ -288,7 +254,9 @@ void rtc_lld_get_alarm(RTCDriver *rtcp,
   (void)rtcp;
   (void)alarm;
 
-  rtc_lld_wait_sync();
+  /* Required because access to ALR.*/
+  rtc_lld_apb1_sync();
+
   alarmspec->tv_sec = ((RTC->ALRH << 16) + RTC->ALRL);
 }
 
@@ -304,25 +272,20 @@ void rtc_lld_get_alarm(RTCDriver *rtcp,
  */
 void rtc_lld_set_callback(RTCDriver *rtcp, rtccb_t callback) {
 
-  PWR->CR |= PWR_CR_DBP;
-  rtc_lld_acquire();
   if (callback != NULL) {
+
+    /* IRQ sources enabled only after setting up the callback.*/
     rtcp->callback = callback;
 
-    /* Interrupts are enabled only after setting up the callback, this
-       way there is no need to check for the NULL callback pointer inside
-       the IRQ handler.*/
     RTC->CRL &= ~(RTC_CRL_OWF | RTC_CRL_ALRF | RTC_CRL_SECF);
-    nvicEnableVector(RTC_IRQn, CORTEX_PRIORITY_MASK(STM32_RTC_IRQ_PRIORITY));
-    RTC->CRH |= RTC_CRH_OWIE | RTC_CRH_ALRIE | RTC_CRH_SECIE;
+    RTC->CRH = RTC_CRH_OWIE | RTC_CRH_ALRIE | RTC_CRH_SECIE;
   }
   else {
-    nvicDisableVector(RTC_IRQn);
-    RTC->CRL &= ~(RTC_CRL_OWF | RTC_CRL_ALRF | RTC_CRL_SECF);
-    RTC->CRH &= ~(RTC_CRH_OWIE | RTC_CRH_ALRIE | RTC_CRH_SECIE);
+    RTC->CRH = 0;
+
+    /* Callback set to NULL only after disabling the IRQ sources.*/
+    rtcp->callback = NULL;
   }
-  rtc_lld_release();
-  PWR->CR &= ~PWR_CR_DBP;
 }
 
 #endif /* HAL_USE_RTC */
diff --git a/os/hal/platforms/STM32/RTCv1/rtc_lld.h b/os/hal/platforms/STM32/RTCv1/rtc_lld.h
index aaf639492..6f55ab573 100644
--- a/os/hal/platforms/STM32/RTCv1/rtc_lld.h
+++ b/os/hal/platforms/STM32/RTCv1/rtc_lld.h
@@ -103,12 +103,10 @@ typedef void (*rtccb_t)(RTCDriver *rtcp, rtcevent_t event);
  * @brief   Structure representing an RTC callbacks config.
  */
 struct RTCCallbackConfig{
-#if RTC_SUPPORTS_CALLBACKS
   /**
    * @brief Generic RTC callback pointer.
    */
   rtccb_t           callback;
-#endif /* RTC_SUPPORTS_CALLBACKS */
 };
 
 /**
diff --git a/os/hal/platforms/STM32F1xx/hal_lld.c b/os/hal/platforms/STM32F1xx/hal_lld.c
index 0112d7eaa..f903106cb 100644
--- a/os/hal/platforms/STM32F1xx/hal_lld.c
+++ b/os/hal/platforms/STM32F1xx/hal_lld.c
@@ -46,8 +46,8 @@
  */
 static void hal_lld_backup_domain_init(void) {
 
-  /* Backup domain access enabled during initialization.*/
-  PWR->CR |= PWR_CR_DBP;
+  /* Backup domain access enabled and left open.*/
+  PWR->CR = PWR_CR_DBP;
 
   /* If enabled then the LSE is started.*/
 #if STM32_LSE_ENABLED
@@ -72,9 +72,6 @@ static void hal_lld_backup_domain_init(void) {
     RCC->BDCR |= RCC_BDCR_RTCEN;
   }
 #endif /* STM32_RTCSEL != STM32_RTCSEL_NOCLOCK */
-
-  /*  Backup domain access disabled for operations safety.*/
-  PWR->CR &= ~PWR_CR_DBP;
 }
 
 /*===========================================================================*/
diff --git a/os/hal/platforms/STM32F2xx/hal_lld.c b/os/hal/platforms/STM32F2xx/hal_lld.c
index 7cc24f2a0..8dc079187 100644
--- a/os/hal/platforms/STM32F2xx/hal_lld.c
+++ b/os/hal/platforms/STM32F2xx/hal_lld.c
@@ -46,8 +46,8 @@
  */
 static void hal_lld_backup_domain_init(void) {
 
-  /* Backup domain access enabled during initialization.*/
-  PWR->CR |= PWR_CR_DBP;
+  /* Backup domain access enabled and left open.*/
+  PWR->CR = PWR_CR_DBP;
 
   /* If enabled then the LSE is started.*/
 #if STM32_LSE_ENABLED
@@ -72,9 +72,6 @@ static void hal_lld_backup_domain_init(void) {
     RCC->BDCR |= RCC_BDCR_RTCEN;
   }
 #endif /* STM32_RTCSEL != STM32_RTCSEL_NOCLOCK */
-
-  /*  Backup domain access disabled for operations safety.*/
-  PWR->CR &= ~PWR_CR_DBP;
 }
 
 /*===========================================================================*/
diff --git a/os/hal/platforms/STM32F4xx/hal_lld.c b/os/hal/platforms/STM32F4xx/hal_lld.c
index 00c560f08..3dd520c2c 100644
--- a/os/hal/platforms/STM32F4xx/hal_lld.c
+++ b/os/hal/platforms/STM32F4xx/hal_lld.c
@@ -46,8 +46,8 @@
  */
 static void hal_lld_backup_domain_init(void) {
 
-  /* Backup domain access enabled during initialization.*/
-  PWR->CR |= PWR_CR_DBP;
+  /* Backup domain access enabled and left open.*/
+  PWR->CR = PWR_CR_DBP;
 
   /* If enabled then the LSE is started.*/
 #if STM32_LSE_ENABLED
@@ -72,9 +72,6 @@ static void hal_lld_backup_domain_init(void) {
     RCC->BDCR |= RCC_BDCR_RTCEN;
   }
 #endif /* STM32_RTCSEL != STM32_RTCSEL_NOCLOCK */
-
-  /*  Backup domain access disabled for operations safety.*/
-  PWR->CR &= ~PWR_CR_DBP;
 }
 
 /*===========================================================================*/
diff --git a/os/hal/platforms/STM32L1xx/hal_lld.c b/os/hal/platforms/STM32L1xx/hal_lld.c
index 4e1b385a3..e4b21ede3 100644
--- a/os/hal/platforms/STM32L1xx/hal_lld.c
+++ b/os/hal/platforms/STM32L1xx/hal_lld.c
@@ -46,8 +46,8 @@
  */
 static void hal_lld_backup_domain_init(void) {
 
-  /* Backup domain access enabled during initialization.*/
-  PWR->CR |= PWR_CR_DBP;
+  /* Backup domain access enabled and left open.*/
+  PWR->CR = PWR_CR_DBP;
 
   /* If enabled then the LSE is started.*/
 #if STM32_LSE_ENABLED
@@ -72,9 +72,6 @@ static void hal_lld_backup_domain_init(void) {
     RCC->CSR |= RCC_CSR_RTCEN;
   }
 #endif /* STM32_RTCSEL != STM32_RTCSEL_NOCLOCK */
-
-  /*  Backup domain access disabled for operations safety.*/
-  PWR->CR &= ~PWR_CR_DBP;
 }
 
 /*===========================================================================*/
diff --git a/os/hal/src/rtc.c b/os/hal/src/rtc.c
index d7750001d..1f463eb38 100644
--- a/os/hal/src/rtc.c
+++ b/os/hal/src/rtc.c
@@ -141,8 +141,8 @@ void rtcGetAlarm(RTCDriver *rtcp,
 #if RTC_SUPPORTS_CALLBACKS || defined(__DOXYGEN__)
 /**
  * @brief   Enables or disables RTC callbacks.
- * @details This function enables or disables callbacks, use a @p NULL pointer
- *          in order to disable a callback.
+ * @details This function enables or disables the callback, use a @p NULL
+ *          pointer in order to disable it.
  *
  * @param[in] rtcp      pointer to RTC driver structure
  * @param[in] callback  callback function pointer or @p NULL
diff --git a/todo.txt b/todo.txt
index c1325f5f7..8079a4cbc 100644
--- a/todo.txt
+++ b/todo.txt
@@ -5,38 +5,43 @@ X = In progress, some work done.
 ? = Not sure if worth the effort or useful at all.
 N = Decided against.
 
-Current Pipeline (2.3.x):
-* I2C device driver class support and at least one implementation.
-* Consistency check of all halconf.h files.
-* Consistency check of all STM32xx mcuconf.h files.
-* Revision of the RTCv1 driver implementation.
-* Fixing issue with Simulator and CH_DBG_SYSTEM_STATE_CHECK option.
-X STM32F2 validation (so far done testing on STM32F4).
-X Revision of the RTCv2 driver implementation.
-- SDC driver port to STM32F2 and STM32F4.
-- CAN driver test on STM32F4.
+Current Pipeline (2.4.0):
+X Revision of the RTCv1 driver implementation.
+- Posix simulator tickets and test.
+- Complete test cycle.
+- Complete documentation cycle.
 
-Within 2.x.x
-- Nios II support.
-- Update C++ wrapper.
-- FatFs 0.9x integration.
-- Software I2C implementation using a GPT instance for timings.
-- LPC17xx support.
-- NUC120 support.
-- MMC_SPI driver speedup.
-- Static memory allocation hook macros in kernel code.
-- MAC driver for STM32F107, STM32F2xx, STM32F4xx.
-- USB driver model revision.
-  ? USB double buffering support for STM32 implementation.
-  X Evaluate using DMA channels for buffer copy.
-X File System infrastructure.
-X Implement the "transmission end" serial driver event on those platforms
-  supporting the feature, so far only done in STM32 driver.
+Version 2.4.1
+X STM32F2 validation (so far testing done on STM32F4 only).
+X Revision of the RTCv2 driver implementation.
+X SDC driver port to STM32F2 and STM32F4.
+- CAN2 support and CAN driver test on STM32F2/F4.
+
+Within 2.5.x:
 - Revision of scheduling strategy for threads at equal priority.
-- Add a chSysIntegrityCheck() API.
+- Add a chSysIntegrityCheck() API to the kernel.
 - Add a CH_THREAD macro for threads declaration in order to hide
   compiler-specific optimizations for thread functions. All demos will have
   to be updated.
+- Runtime errors manager in HAL.
+- Critical errors manager in HAL (to replace or complement assertions).
+- MMC_SPI driver speedup.
+- USB driver model revision.
+- MAC driver for STM32F107, STM32F2xx, STM32F4xx.
+- STM32 OTG USB cell support for CL, F2, F4 devices.
+- Add ADC3 support to the STM32 ADC driver.
+- Update C++ wrapper.
+- FatFs 0.9x integration.
+- Nios II support.
+- LPC17xx support.
+- NUC120 support.
+
+Within 2.x.x
+- Software I2C implementation using a GPT instance for timings.
+- Static memory allocation hook macros in kernel code.
+X File System infrastructure.
+X Implement the "transmission end" serial driver event on those platforms
+  supporting the feature, so far only done in STM32 driver.
 - Test suite overhaul, the API should be more generic in order to be used
   with different subsystems and not just the kernel.
 - Reduce number of demos globally, add demos to a repository or on web site.
@@ -45,8 +50,6 @@ X Implement the "transmission end" serial driver event on those platforms
 - New device driver models: Clock, Systick, WDG, DAC, Power Monitor.
 - Add UART4 support to the STM32 UART driver (CL line only, HD has a nasty
   shared interrupt).
-- STM32 OTG USB cell support for CL, F2, F4 devices.
-- Add ADC3 support to the STM32 ADC driver.
 - Shared DMA channels support in the STM8L HAL.
 - Device drivers for STM8/STM8L (ADC, PWM, bring them on par with STM32).
 - Device drivers for LPC1xxx (ADC, PWM, bring them on par with STM32).