diff --git a/os/sb/user/sbuser.h b/os/sb/user/sbuser.h
index e5232f9ed..4d1b35e05 100644
--- a/os/sb/user/sbuser.h
+++ b/os/sb/user/sbuser.h
@@ -168,7 +168,7 @@ typedef uint32_t eventflags_t;
 
 #define __syscall0rr(x)                                                     \
   register uint32_t r0 asm ("r0");                                          \
-  register uint32_t r0 asm ("r1");                                          \
+  register uint32_t r1 asm ("r1");                                          \
   asm volatile ("svc " #x : "=r" (r0), "=r" (r1) : : "memory")
 
 #define __syscall1r(x, p1)                                                  \
@@ -177,7 +177,7 @@ typedef uint32_t eventflags_t;
 
 #define __syscall1rr(x, p1)                                                 \
   register uint32_t r0 asm ("r0") = (uint32_t)(p1);                         \
-  register uint32_t r0 asm ("r1");                                          \
+  register uint32_t r1 asm ("r1");                                          \
   asm volatile ("svc " #x : "=r" (r0), "=r" (r1) :                          \
                              "r" (r0) :                                     \
                              "memory")
diff --git a/os/sb/vio/sbvio.h b/os/sb/vio/sbvio.h
index 0f4a78b0b..73fa50d0b 100644
--- a/os/sb/vio/sbvio.h
+++ b/os/sb/vio/sbvio.h
@@ -100,6 +100,22 @@ typedef struct vio_conf {
 /* Module macros.                                                            */
 /*===========================================================================*/
 
+/**
+ * @brief   Sub-code part of VIO calls 1st parameter.
+ *
+ * @param[n] n          the VIO 1st parameter
+ * @return              The VIO call sub-code.
+ */
+#define VIO_CALL_SUBCODE(n)     ((uint32_t)(n) & 0xFFU)
+
+/**
+ * @brief   Unit identifier part of VIO calls 1st parameter.
+ *
+ * @param[n] n          the VIO 1st parameter
+ * @return              The VIO call unit identifier.
+ */
+#define VIO_CALL_UNIT(n)        ((uint32_t)(n) >> 24)
+
 /*===========================================================================*/
 /* External declarations.                                                    */
 /*===========================================================================*/
diff --git a/os/sb/vio/sbvio_gpio.c b/os/sb/vio/sbvio_gpio.c
index bbe53210d..f967474ac 100644
--- a/os/sb/vio/sbvio_gpio.c
+++ b/os/sb/vio/sbvio_gpio.c
@@ -55,8 +55,8 @@
 
 void sb_fastc_vio_gpio(struct port_extctx *ectxp) {
   sb_class_t *sbp = (sb_class_t *)chThdGetSelfX()->ctx.syscall.p;
-  uint32_t sub = (unsigned)ectxp->r0;
-  uint32_t unit = (unsigned)ectxp->r1;
+  uint32_t sub  = VIO_CALL_SUBCODE(ectxp->r0);
+  uint32_t unit = VIO_CALL_UNIT(ectxp->r0);
   const vio_gpio_unit_t *unitp;
   ectxp->r0 = 0U;
 
@@ -69,25 +69,25 @@ void sb_fastc_vio_gpio(struct port_extctx *ectxp) {
   switch (sub) {
   case SB_VGPIO_WRITE:
     if ((unitp->permissions & VIO_GPIO_PERM_WRITE) != 0U) {
-      palWriteGroup(unitp->port, unitp->mask, unitp->offset, ectxp->r2);
+      palWriteGroup(unitp->port, unitp->mask, unitp->offset, ectxp->r1);
     }
     break;
   case SB_VGPIO_SET:
     if ((unitp->permissions & VIO_GPIO_PERM_WRITE) != 0U) {
       uint32_t val = palReadGroup(unitp->port, unitp->mask, unitp->offset);
-      palWriteGroup(unitp->port, unitp->mask, unitp->offset, ectxp->r2 | val);
+      palWriteGroup(unitp->port, unitp->mask, unitp->offset, ectxp->r1 | val);
     }
     break;
   case SB_VGPIO_CLEAR:
     if ((unitp->permissions & VIO_GPIO_PERM_WRITE) != 0U) {
       uint32_t val = palReadGroup(unitp->port, unitp->mask, unitp->offset);
-      palWriteGroup(unitp->port, unitp->mask, unitp->offset, ectxp->r2 & ~val);
+      palWriteGroup(unitp->port, unitp->mask, unitp->offset, ectxp->r1 & ~val);
     }
     break;
   case SB_VGPIO_TOGGLE:
     if ((unitp->permissions & VIO_GPIO_PERM_WRITE) != 0U) {
       uint32_t val = palReadGroup(unitp->port, unitp->mask, unitp->offset);
-      palWriteGroup(unitp->port, unitp->mask, unitp->offset, ectxp->r2 ^ val);
+      palWriteGroup(unitp->port, unitp->mask, unitp->offset, ectxp->r1 ^ val);
     }
     break;
   case SB_VGPIO_READLATCH:
diff --git a/os/sb/vio/sbvio_spi.c b/os/sb/vio/sbvio_spi.c
index 6b2919acb..77030b3b8 100644
--- a/os/sb/vio/sbvio_spi.c
+++ b/os/sb/vio/sbvio_spi.c
@@ -62,8 +62,8 @@ static void vspi_cb(void *ip) {
 
 void sb_sysc_vio_spi(struct port_extctx *ectxp) {
   sb_class_t *sbp = (sb_class_t *)chThdGetSelfX()->ctx.syscall.p;
-  uint32_t sub  = ectxp->r0;
-  uint32_t unit = ectxp->r1;
+  uint32_t sub  = VIO_CALL_SUBCODE(ectxp->r0);
+  uint32_t unit = VIO_CALL_UNIT(ectxp->r0);
   ectxp->r0 = (uint32_t)CH_RET_INNER_ERROR;
   const vio_spi_unit_t *unitp;
 
@@ -108,8 +108,8 @@ void sb_sysc_vio_spi(struct port_extctx *ectxp) {
 
 void sb_fastc_vio_spi(struct port_extctx *ectxp) {
   sb_class_t *sbp = (sb_class_t *)chThdGetSelfX()->ctx.syscall.p;
-  uint32_t sub  = ectxp->r0;
-  uint32_t unit = ectxp->r1;
+  uint32_t sub  = VIO_CALL_SUBCODE(ectxp->r0);
+  uint32_t unit = VIO_CALL_UNIT(ectxp->r0);
   const vio_spi_unit_t *unitp;
 
   /* Returned value in case of error or illegal sub-code.*/
@@ -130,7 +130,7 @@ void sb_fastc_vio_spi(struct port_extctx *ectxp) {
   switch (sub) {
   case SB_VSPI_SETCFG:
     {
-      uint32_t conf = ectxp->r2;
+      uint32_t conf = ectxp->r1;
       const vio_spi_config_t *confp;
 
       /* Check on configuration index.*/
diff --git a/os/sb/vio/sbvio_uart.c b/os/sb/vio/sbvio_uart.c
index 540ea2ab6..b134b7535 100644
--- a/os/sb/vio/sbvio_uart.c
+++ b/os/sb/vio/sbvio_uart.c
@@ -62,8 +62,8 @@ static void vuart_cb(void *ip) {
 
 void sb_sysc_vio_uart(struct port_extctx *ectxp) {
   sb_class_t *sbp = (sb_class_t *)chThdGetSelfX()->ctx.syscall.p;
-  uint32_t sub  = ectxp->r0;
-  uint32_t unit = ectxp->r1;
+  uint32_t sub  = VIO_CALL_SUBCODE(ectxp->r0);
+  uint32_t unit = VIO_CALL_UNIT(ectxp->r0);
   ectxp->r0 = (uint32_t)CH_RET_INNER_ERROR;
   const vio_uart_unit_t *unitp;
 
@@ -108,8 +108,8 @@ void sb_sysc_vio_uart(struct port_extctx *ectxp) {
 
 void sb_fastc_vio_uart(struct port_extctx *ectxp) {
   sb_class_t *sbp = (sb_class_t *)chThdGetSelfX()->ctx.syscall.p;
-  uint32_t sub  = ectxp->r0;
-  uint32_t unit = ectxp->r1;
+  uint32_t sub  = VIO_CALL_SUBCODE(ectxp->r0);
+  uint32_t unit = VIO_CALL_UNIT(ectxp->r0);
   const vio_uart_unit_t *unitp;
 
   /* Returned value in case of error or illegal sub-code.*/
@@ -130,7 +130,7 @@ void sb_fastc_vio_uart(struct port_extctx *ectxp) {
   switch (sub) {
   case SB_VUART_SETCFG:
     {
-      uint32_t conf = ectxp->r2;
+      uint32_t conf = ectxp->r1;
       const vio_uart_config_t *confp;
 
       /* Check on configuration index.*/
@@ -172,8 +172,8 @@ void sb_fastc_vio_uart(struct port_extctx *ectxp) {
     }
   case SB_VUART_READ:
     {
-      uint8_t *buffer = (uint8_t *)ectxp->r2;
-      size_t n = (size_t)ectxp->r3;
+      uint8_t *buffer = (uint8_t *)ectxp->r1;
+      size_t n = (size_t)ectxp->r2;
 
       if (!sb_is_valid_write_range(sbp, buffer, n)) {
         ectxp->r0 = (uint32_t)0;
@@ -186,8 +186,8 @@ void sb_fastc_vio_uart(struct port_extctx *ectxp) {
     }
   case SB_VUART_WRITE:
     {
-      const uint8_t *buffer = (const uint8_t *)ectxp->r2;
-      size_t n = (size_t)ectxp->r3;
+      const uint8_t *buffer = (const uint8_t *)ectxp->r1;
+      size_t n = (size_t)ectxp->r2;
 
       if (!sb_is_valid_read_range(sbp, buffer, n)) {
         ectxp->r0 = (uint32_t)0;
@@ -205,13 +205,13 @@ void sb_fastc_vio_uart(struct port_extctx *ectxp) {
     }
   case SB_VUART_PUT:
     {
-      sioPutX(unitp->siop, (uint_fast16_t)ectxp->r2);
+      sioPutX(unitp->siop, (uint_fast16_t)ectxp->r1);
       ectxp->r0 = (uint32_t)0;
       break;
     }
   case SB_VUART_WREN:
     {
-      sioWriteEnableFlagsX(unitp->siop, (sioevents_t)ectxp->r2);
+      sioWriteEnableFlagsX(unitp->siop, (sioevents_t)ectxp->r1);
       ectxp->r0 = (uint32_t)0;
       break;
     }
@@ -223,7 +223,7 @@ void sb_fastc_vio_uart(struct port_extctx *ectxp) {
   case SB_VUART_GCEVT:
     {
       ectxp->r0 = (uint32_t)sioGetAndClearEventsX(unitp->siop,
-                                                  (sioevents_t)ectxp->r2);
+                                                  (sioevents_t)ectxp->r1);
       break;
     }
   case SB_VUART_GEVT:
diff --git a/os/xhal/ports/vio/hal_lld.h b/os/xhal/ports/vio/hal_lld.h
index aa82012b1..fe89993e8 100644
--- a/os/xhal/ports/vio/hal_lld.h
+++ b/os/xhal/ports/vio/hal_lld.h
@@ -80,6 +80,15 @@ typedef unsigned halclkpt_t;
 #define __MK_VECTOR(n)      __sb_vector##n
 #define MK_VECTOR(n)        __MK_VECTOR(n)
 
+/**
+ * @brief   Builds a VIO call 1st parameter.
+ *
+ * @param[in] c         the sub-code
+ * @param[in] u         the unit identifier
+ * @return              The formatted VIO call 1st parameter.
+ */
+#define VIO_CALL(c, u) (((uint32_t)(u) << 24) | (uint32_t)(c))
+
 /*===========================================================================*/
 /* External declarations.                                                    */
 /*===========================================================================*/
diff --git a/os/xhal/ports/vio/hal_pal_lld.h b/os/xhal/ports/vio/hal_pal_lld.h
index 917110953..9e0cb6213 100644
--- a/os/xhal/ports/vio/hal_pal_lld.h
+++ b/os/xhal/ports/vio/hal_pal_lld.h
@@ -233,39 +233,39 @@ extern "C" {
 __attribute__((always_inline))
 static inline uint32_t __pal_lld_readport(ioportid_t port) {
 
-  __syscall2r(96, SB_VGPIO_READ, port);
+  __syscall1r(96, VIO_CALL(SB_VGPIO_READ, port));
   return (ioportmask_t)r0;
 }
 
 __attribute__((always_inline))
 static inline uint32_t __pal_lld_readlatch(ioportid_t port) {
 
-  __syscall2r(96, SB_VGPIO_READLATCH, port);
+  __syscall1r(96, VIO_CALL(SB_VGPIO_READLATCH, port));
   return (ioportmask_t)r0;
 }
 
 __attribute__((always_inline))
 static inline void __pal_lld_writeport(ioportid_t port, uint32_t bits) {
 
-  __syscall3r(96, SB_VGPIO_WRITE, port, bits);
+  __syscall2r(96, VIO_CALL(SB_VGPIO_WRITE, port), bits);
 }
 
 __attribute__((always_inline))
 static inline void __pal_lld_setport(ioportid_t port, uint32_t bits) {
 
-  __syscall3r(96, SB_VGPIO_SET, port, bits);
+  __syscall2r(96, VIO_CALL(SB_VGPIO_SET, port), bits);
 }
 
 __attribute__((always_inline))
 static inline void __pal_lld_clearport(ioportid_t port, uint32_t bits) {
 
-  __syscall3r(96, SB_VGPIO_CLEAR, port, bits);
+  __syscall2r(96, VIO_CALL(SB_VGPIO_CLEAR, port), bits);
 }
 
 __attribute__((always_inline))
 static inline void __pal_lld_toggleport(ioportid_t port, uint32_t bits) {
 
-  __syscall3r(96, SB_VGPIO_TOGGLE, port, bits);
+  __syscall2r(96, VIO_CALL(SB_VGPIO_TOGGLE, port), bits);
 }
 
 #endif /* HAL_USE_PAL == TRUE */
diff --git a/os/xhal/ports/vio/hal_sio_lld.c b/os/xhal/ports/vio/hal_sio_lld.c
index 3da2a348a..54230d73f 100644
--- a/os/xhal/ports/vio/hal_sio_lld.c
+++ b/os/xhal/ports/vio/hal_sio_lld.c
@@ -66,21 +66,21 @@ static const SIOConfig default_config = {
 CC_FORCE_INLINE
 static inline uint32_t __sio_vuart_init(uint32_t nvuart) {
 
-  __syscall2r(225, SB_VUART_INIT, nvuart);
+  __syscall1r(225, VIO_CALL(SB_VUART_INIT, nvuart));
   return (uint32_t)r0;
 }
 
 CC_FORCE_INLINE
 static inline uint32_t __sio_vuart_deinit(uint32_t nvuart) {
 
-  __syscall2r(225, SB_VUART_DEINIT, nvuart);
+  __syscall1r(225, VIO_CALL(SB_VUART_DEINIT, nvuart));
   return (uint32_t)r0;
 }
 
 CC_FORCE_INLINE
 static inline uint32_t __sio_vuart_setcfg(uint32_t nvuart, uint32_t ncfg) {
 
-  __syscall3r(225, SB_VUART_SETCFG, nvuart, ncfg);
+  __syscall2r(225, VIO_CALL(SB_VUART_SETCFG, nvuart), ncfg);
   return (uint32_t)r0;
 }
 
@@ -219,7 +219,7 @@ msg_t sio_lld_configure(SIODriver *siop, const SIOConfig *config) {
  */
 bool sio_lld_is_rx_empty(SIODriver *siop) {
 
-  __syscall2r(97, SB_VUART_ISRXE, siop->nvuart);
+  __syscall1r(97, VIO_CALL(SB_VUART_ISRXE, siop->nvuart));
   osalDbgAssert(r0 != (uint32_t)-1, "unexpected failure");
 
   return (bool)r0;
@@ -237,7 +237,7 @@ bool sio_lld_is_rx_empty(SIODriver *siop) {
  */
 bool sio_lld_is_rx_idle(SIODriver *siop) {
 
-  __syscall2r(97, SB_VUART_ISRXI, siop->nvuart);
+  __syscall1r(97, VIO_CALL(SB_VUART_ISRXI, siop->nvuart));
   osalDbgAssert(r0 != (uint32_t)-1, "unexpected failure");
 
   return (bool)r0;
@@ -257,7 +257,7 @@ bool sio_lld_is_rx_idle(SIODriver *siop) {
  */
 bool sio_lld_has_rx_errors(SIODriver *siop) {
 
-  __syscall2r(97, SB_VUART_HASERR, siop->nvuart);
+  __syscall1r(97, VIO_CALL(SB_VUART_HASERR, siop->nvuart));
   osalDbgAssert(r0 != (uint32_t)-1, "unexpected failure");
 
   return (bool)r0;
@@ -275,7 +275,7 @@ bool sio_lld_has_rx_errors(SIODriver *siop) {
  */
 bool sio_lld_is_tx_full(SIODriver *siop) {
 
-  __syscall2r(97, SB_VUART_ISTXF, siop->nvuart);
+  __syscall1r(97, VIO_CALL(SB_VUART_ISTXF, siop->nvuart));
   osalDbgAssert(r0 != (uint32_t)-1, "unexpected failure");
 
   return (bool)r0;
@@ -293,7 +293,7 @@ bool sio_lld_is_tx_full(SIODriver *siop) {
  */
 bool sio_lld_is_tx_ongoing(SIODriver *siop) {
 
-  __syscall2r(97, SB_VUART_ISTXO, siop->nvuart);
+  __syscall1r(97, VIO_CALL(SB_VUART_ISTXO, siop->nvuart));
   osalDbgAssert(r0 != (uint32_t)-1, "unexpected failure");
 
   return (bool)r0;
@@ -306,7 +306,7 @@ bool sio_lld_is_tx_ongoing(SIODriver *siop) {
  */
 void sio_lld_update_enable_flags(SIODriver *siop) {
 
-  __syscall3r(97, SB_VUART_WREN, siop->nvuart, siop->enabled);
+  __syscall2r(97, VIO_CALL(SB_VUART_WREN, siop->nvuart), siop->enabled);
   osalDbgAssert(r0 != (uint32_t)-1, "unexpected failure");
 }
 
@@ -320,7 +320,7 @@ void sio_lld_update_enable_flags(SIODriver *siop) {
  */
 sioevents_t sio_lld_get_and_clear_errors(SIODriver *siop) {
 
-  __syscall2r(97, SB_VUART_GCERR, siop->nvuart);
+  __syscall1r(97, VIO_CALL(SB_VUART_GCERR, siop->nvuart));
   osalDbgAssert(r0 != (uint32_t)-1, "unexpected failure");
 
   return (sioevents_t)r0;
@@ -337,7 +337,7 @@ sioevents_t sio_lld_get_and_clear_errors(SIODriver *siop) {
  */
 sioevents_t sio_lld_get_and_clear_events(SIODriver *siop, sioevents_t events) {
 
-  __syscall3r(97, SB_VUART_GCEVT, siop->nvuart, events);
+  __syscall2r(97, VIO_CALL(SB_VUART_GCEVT, siop->nvuart), events);
   osalDbgAssert(r0 != (uint32_t)-1, "unexpected failure");
 
   return (sioevents_t)r0;
@@ -353,7 +353,7 @@ sioevents_t sio_lld_get_and_clear_events(SIODriver *siop, sioevents_t events) {
  */
 sioevents_t sio_lld_get_events(SIODriver *siop) {
 
-  __syscall2r(97, SB_VUART_GEVT, siop->nvuart);
+  __syscall1r(97, VIO_CALL(SB_VUART_GEVT, siop->nvuart));
   osalDbgAssert(r0 != (uint32_t)-1, "unexpected failure");
 
   return (sioevents_t)r0;
@@ -372,7 +372,7 @@ sioevents_t sio_lld_get_events(SIODriver *siop) {
  */
 size_t sio_lld_read(SIODriver *siop, uint8_t *buffer, size_t n) {
 
-  __syscall4r(97, SB_VUART_READ, siop->nvuart, buffer, n);
+  __syscall3r(97, VIO_CALL(SB_VUART_READ, siop->nvuart), buffer, n);
   osalDbgAssert(r0 != (uint32_t)-1, "unexpected failure");
 
   return (size_t)r0;
@@ -391,7 +391,7 @@ size_t sio_lld_read(SIODriver *siop, uint8_t *buffer, size_t n) {
  */
 size_t sio_lld_write(SIODriver *siop, const uint8_t *buffer, size_t n) {
 
-  __syscall4r(97, SB_VUART_WRITE, siop->nvuart, buffer, n);
+  __syscall3r(97, VIO_CALL(SB_VUART_WRITE, siop->nvuart), buffer, n);
   osalDbgAssert(r0 != (uint32_t)-1, "unexpected failure");
 
   return (size_t)r0;
@@ -408,7 +408,7 @@ size_t sio_lld_write(SIODriver *siop, const uint8_t *buffer, size_t n) {
  */
 msg_t sio_lld_get(SIODriver *siop) {
 
-  __syscall2r(97, SB_VUART_GET, siop->nvuart);
+  __syscall1r(97, VIO_CALL(SB_VUART_GET, siop->nvuart));
   osalDbgAssert(r0 != (uint32_t)-1, "unexpected failure");
 
   return (size_t)r0;
@@ -425,7 +425,7 @@ msg_t sio_lld_get(SIODriver *siop) {
  */
 void sio_lld_put(SIODriver *siop, uint_fast16_t data) {
 
-  __syscall3r(97, SB_VUART_PUT, siop->nvuart, data);
+  __syscall2r(97, VIO_CALL(SB_VUART_PUT, siop->nvuart), data);
   osalDbgAssert(r0 != (uint32_t)-1, "unexpected failure");
 }
 
@@ -445,7 +445,7 @@ void sio_lld_put(SIODriver *siop, uint_fast16_t data) {
  */
 msg_t sio_lld_control(SIODriver *siop, unsigned int operation, void *arg) {
 
-  __syscall4r(97, SB_VUART_CTL, siop->nvuart, operation, arg);
+  __syscall3r(97, VIO_CALL(SB_VUART_CTL, siop->nvuart), operation, arg);
   osalDbgAssert(r0 != (uint32_t)-1, "unexpected failure");
 
   return (msg_t)r0;
@@ -462,7 +462,7 @@ void sio_lld_serve_interrupt(SIODriver *siop) {
   sioevents_t events;
 
 #if SIO_USE_SYNCHRONIZATION == TRUE
-  __syscall2rr(97, SB_VUART_GEVT, siop->nvuart);
+  __syscall1rr(97, VIO_CALL(SB_VUART_GEVT, siop->nvuart));
   osalDbgAssert(r0 != (uint32_t)-1, "unexpected failure");
 
   /* Processing enabled events, if any.*/