Merge pull request stm32duino#202 from fpistm/micros

Improves micros() accuracy using SysTick COUNTFLAG

Author: fpistm

cores/arduino/stm32/clock.c

@@ -35,84 +35,28 @@
   *
   ******************************************************************************
   */
-/** @addtogroup CMSIS
-  * @{
-  */
-
-/** @addtogroup stm32f4xx_system
-  * @{
-  */
-
-/** @addtogroup STM32F4xx_System_Private_Includes
-  * @{
-  */
 #include "stm32_def.h"
 
 #ifdef __cplusplus
  extern "C" {
 #endif
 
-/**
-  * @}
-  */
-
-/** @addtogroup STM32F4xx_System_Private_TypesDefinitions
-  * @{
-  */
-
-/**
-  * @}
-  */
-
-/** @addtogroup STM32F4xx_System_Private_Defines
-  * @{
-  */
-
-/**
-  * @}
-  */
-
-/** @addtogroup STM32F4xx_System_Private_Macros
-  * @{
-  */
-
-/**
-  * @}
-  */
-
-/** @addtogroup STM32F4xx_System_Private_Variables
-  * @{
-  */
-
-/**
-  * @}
-  */
-
-/** @addtogroup STM32F4xx_System_Private_FunctionPrototypes
-  * @{
-  */
-
-/**
-  * @}
-  */
-
 /**
   * @brief  Function called to read the current micro second
   * @param  None
   * @retval None
   */
 uint32_t GetCurrentMicro(void)
 {
-  uint32_t m0 = HAL_GetTick();
-  uint32_t u0 = SysTick->LOAD - SysTick->VAL;
-  uint32_t m1 = HAL_GetTick();
-  uint32_t u1 = SysTick->LOAD - SysTick->VAL;
-
-  if (m1 > m0) {
-    return ( m1 * 1000 + (u1 * 1000) / SysTick->LOAD);
-  } else {
-    return ( m0 * 1000 + (u0 * 1000) / SysTick->LOAD);
+  /* Ensure COUNTFLAG is reset by reading SysTick control and status register */
+  LL_SYSTICK_IsActiveCounterFlag();
+  uint32_t m = HAL_GetTick();
+  uint32_t u = SysTick->LOAD - SysTick->VAL;
+  if(LL_SYSTICK_IsActiveCounterFlag()) {
+    m = HAL_GetTick();
+    u = SysTick->LOAD - SysTick->VAL;
   }
+  return ( m * 1000 + (u * 1000) / SysTick->LOAD);
 }
 
 /**
@@ -176,17 +120,6 @@ void delayInsideIT(uint32_t delay_us)
 #endif
 }
 
-/**
-  * @}
-  */
-
-/**
-  * @}
-  */
-
-/**
-  * @}
-  */
 #ifdef __cplusplus
 }
 #endif