RTOS2: Update documentation for OS Tick

CMSIS/DoxyGen/RTOS2/src/cmsis_os2_tick.txt

@@ -8,15 +8,20 @@
 The <b>OS Tick API</b> is an interface to a system timer that generates the Kernel Ticks.
 
 All Cortex-M processors provide an unified System Tick Timer that is typically used to generate the RTOS Kernel Tick. 
+
+\if ARMCA
 The Cortex-A processors do not implement an unified system timer and required a device specific implementation. 
+\endif
 
-CMSIS-RTOS2 provides in the directory \ref directory "CMSIS/RTOS2/Source" the several OS Tick implementations that can be used by any RTOS kernel.
+CMSIS-RTOS2 provides in the directory \ref directory "CMSIS/RTOS2/Source" several OS Tick implementations that can be used by any RTOS kernel.
 
 Filename                 | OS Tick Implementation for...
 :------------------------|:-----------------------------------------------------------------------
 \b %os_systick.c         | Cortex-M SysTick timer
+\if ARMCA
 \b %os_tick_gtim.c       | Cortex-A Generic Timer (available in some devices)
 \b %os_tick_ptim.c       | Cortex-A Private Timer (available in some devices)
+\endif
 
 \note The above OS Tick source files implement \c weak functions which may be overwritten by user-specific implementations.
 
@@ -47,25 +52,25 @@ static uint8_t PendST;
 int32_t  OS_Tick_Setup (uint32_t freq, IRQHandler_t handler) {
   (void)handler;
   uint32_t load;
-
+ 
   if (freq == 0U) {
-    return -1;
+    return (-1);
   }
-
+ 
   load = (SystemCoreClock / freq) - 1U;
   if (load > 0x00FFFFFFU) {
-    return -1;
+    return (-1);
   }
-
+ 
   NVIC_SetPriority(SysTick_IRQn, SYSTICK_IRQ_PRIORITY);
-
+ 
   SysTick->CTRL =  SysTick_CTRL_CLKSOURCE_Msk | SysTick_CTRL_TICKINT_Msk;
   SysTick->LOAD =  load;
   SysTick->VAL  =  0U;
-
+ 
   PendST = 0U;
 
-  return 0;
+  return (0);
 }
 \endcode
 */
@@ -147,7 +152,7 @@ Return the numeric value that identifies the interrupt called by the OS Tick tim
 
 \code
 int32_t  OS_Tick_GetIRQn (void) {
-  return SysTick_IRQn;
+  return ((int32_t)SysTick_IRQn);
 }
 \endcode
 */
@@ -165,7 +170,7 @@ This function is used to by the function \ref osKernelGetSysTimerFreq.
 
 \code
 uint32_t OS_Tick_GetClock (void) {
-  return SystemCoreClock;
+  return (SystemCoreClock);
 }
 \endcode
 */
@@ -182,7 +187,7 @@ Return the number of counter ticks between to periodic OS Tick timer interrupts.
 
 \code
 uint32_t OS_Tick_GetInterval (void) {
-  return SysTick->LOAD + 1U;
+  return (SysTick->LOAD + 1U);
 }
 \endcode
 */
@@ -201,8 +206,17 @@ The OS Tick timer counter value is used to by the function \ref osKernelGetSysTi
 
 \code
 uint32_t OS_Tick_GetCount (void) {
-  uint32_t load = SysTick->LOAD;
-  return load - SysTick->VAL;
+  uint32_t val;
+  uint32_t count;
+
+  val = SysTick->VAL;
+  if (val != 0U) {
+    count = (SysTick->LOAD - val) + 1U;
+  } else {
+    count = 0U;
+  }
+
+  return (count);
 }
 \endcode
 */
@@ -219,7 +233,7 @@ Return the state of OS Tick timer interrupt pending bit that indicates timer ove
 
 \code
 uint32_t OS_Tick_GetOverflow (void) {
-  return (SCB->ICSR & SCB_ICSR_PENDSTSET_Msk) >> SCB_ICSR_PENDSTSET_Pos;
+  return ((SCB->ICSR & SCB_ICSR_PENDSTSET_Msk) >> SCB_ICSR_PENDSTSET_Pos);
 }
 \endcode
 */