diff --git a/demos/STM32/RT-STM32G474RE-NUCLEO64-SB_HOST_STATIC/main.c b/demos/STM32/RT-STM32G474RE-NUCLEO64-SB_HOST_STATIC/main.c
index d46e16b0f..69fdfd67f 100644
--- a/demos/STM32/RT-STM32G474RE-NUCLEO64-SB_HOST_STATIC/main.c
+++ b/demos/STM32/RT-STM32G474RE-NUCLEO64-SB_HOST_STATIC/main.c
@@ -26,6 +26,10 @@
 
 #include "startup_defs.h"
 
+
+/* Sandbox objects.*/
+sb_class_t sbx1, sbx2;
+
 /*===========================================================================*/
 /* VHAL-related.                                                             */
 /*===========================================================================*/
@@ -45,7 +49,11 @@ static vio_gpio_units_t gpio_units1 = {
 static vio_uart_units_t uart_units1 = {
   .n        = 1U,
   .units    = {
-    [0]       = {&LPSIOD1}
+    [0]       = {
+      .siop  = &LPSIOD1,
+      .vrqsb = &sbx1,
+      .vrqn  = 8
+    }
   }
 };
 
@@ -162,9 +170,6 @@ static const char *sbx2_envp[] = {
   NULL
 };
 
-/* Sandbox objects.*/
-sb_class_t sbx1, sbx2;
-
 static THD_WORKING_AREA(waUnprivileged1, 512);
 static THD_WORKING_AREA(waUnprivileged2, 512);
 
diff --git a/os/hal/ports/sandbox/hal_sio_lld.c b/os/hal/ports/sandbox/hal_sio_lld.c
index 6a24abf8a..da7ea15b7 100644
--- a/os/hal/ports/sandbox/hal_sio_lld.c
+++ b/os/hal/ports/sandbox/hal_sio_lld.c
@@ -432,10 +432,20 @@ msg_t sio_lld_control(SIODriver *siop, unsigned int operation, void *arg) {
  * @notapi
  */
 void sio_lld_serve_interrupt(SIODriver *siop) {
+  sioevents_t events;
 
-  /* The callback is simply invoked. Letting the driver on the host side
-     decide how to manipulate IRQ sources.*/
-  __sio_callback(siop);
+  __syscall2rr(201, SB_VUART_GCEVT, siop->nvuart);
+  osalDbgAssert((msg_t)r0 == HAL_RET_SUCCESS, "unexpected failure");
+
+  /* Only processing enabled events.*/
+  events = (sioevents_t)r1;
+
+  /* Processing events, if any.*/
+  if (events != (sioevents_t)0) {
+
+    /* The callback is finally invoked.*/
+    __sio_callback(siop);
+  }
 }
 
 #endif /* HAL_USE_SIO == TRUE */
diff --git a/os/sb/host/sb.h b/os/sb/host/sb.h
index 3f787f8f1..37ddabeaf 100644
--- a/os/sb/host/sb.h
+++ b/os/sb/host/sb.h
@@ -36,10 +36,6 @@
 #include "sbsysc.h"
 #include "sbconf.h"
 
-#if (SB_CFG_ENABLE_VIO == TRUE) || defined (__DOXYGEN__)
-#include "sbvio.h"
-#endif
-
 /*===========================================================================*/
 /* Module constants.                                                         */
 /*===========================================================================*/
@@ -172,11 +168,25 @@
 /* Module data structures and types.                                         */
 /*===========================================================================*/
 
+
+/**
+ * @brief   Type of a sandbox object.
+ */
+typedef struct sb_class sb_class_t;
+
 /**
  * @brief   Type of a mask of Virtual IRQs.
  */
 typedef uint32_t sb_vrqmask_t;
 
+#if (SB_CFG_ENABLE_VRQ == TRUE) || defined (__DOXYGEN__)
+#include "sbvrq.h"
+#endif
+
+#if (SB_CFG_ENABLE_VIO == TRUE) || defined (__DOXYGEN__)
+#include "sbvio.h"
+#endif
+
 /**
  * @brief   Type of a sandbox manager global structure.
  */
@@ -262,9 +272,9 @@ typedef struct {
 } sb_config_t;
 
 /**
- * @brief   Type of a sandbox object.
+ * @brief   Structure representing a sandbox object.
  */
-typedef struct {
+struct sb_class {
   /**
    * @brief   Pointer to the sandbox configuration data.
    */
@@ -317,7 +327,7 @@ typedef struct {
    */
   sb_ioblock_t                  io;
 #endif
-} sb_class_t;
+};
 
 /*===========================================================================*/
 /* Module macros.                                                            */
@@ -339,10 +349,6 @@ extern "C" {
 /* Module inline functions.                                                  */
 /*===========================================================================*/
 
-#if (SB_CFG_ENABLE_VRQ == TRUE) || defined (__DOXYGEN__)
-#include "sbvrq.h"
-#endif
-
 #include "sbelf.h"
 #include "sbposix.h"
 #include "sbapi.h"
diff --git a/os/sb/vio/sbvio_uart.c b/os/sb/vio/sbvio_uart.c
index 4ce6861a6..b95958ed4 100644
--- a/os/sb/vio/sbvio_uart.c
+++ b/os/sb/vio/sbvio_uart.c
@@ -50,9 +50,9 @@
 /*===========================================================================*/
 
 static void vuart_cb(SIODriver *siop) {
-  sb_class_t *sbp = (sb_class_t *)siop->arg;
+  const vio_uart_unit_t *unitp = (const vio_uart_unit_t *)siop->arg;
 
-  sbVRQTriggerFromISR(sbp, 1U << SB_CFG_ALARM_VRQ);
+  sbVRQTriggerFromISR(unitp->vrqsb, 1U << unitp->vrqn);
 }
 
 /*===========================================================================*/
@@ -86,12 +86,14 @@ void sb_api_vio_uart(struct port_extctx *ectxp) {
         return;
       }
 
+      /* Specified VUART configuration.*/
       confp = &sbp->config->vioconf->uartconfs->cfgs[conf];
 
+      /* Associating this virtual UART to the SIO driver.*/
+      unitp->siop->arg = (void *)unitp;
+
       msg = sioStart(unitp->siop, confp->siocfgp);
       if (msg == HAL_RET_SUCCESS) {
-        /* Associating this SIO to the sandbox.*/
-        unitp->siop->arg = (sb_class_t *)sbp;
 
         /* Starting with disabled events, enabling the callback.*/
         sioWriteEnableFlags(unitp->siop, SIO_FL_NONE);
diff --git a/os/sb/vio/sbvio_uart.h b/os/sb/vio/sbvio_uart.h
index c7bf97641..616b531bd 100644
--- a/os/sb/vio/sbvio_uart.h
+++ b/os/sb/vio/sbvio_uart.h
@@ -56,6 +56,8 @@
  */
 typedef struct vio_uart_unit {
   SIODriver         *siop;
+  sb_class_t        *vrqsb;
+  unsigned          vrqn;
 } vio_uart_unit_t;
 
 /**