fix us_ticker issue for Nucleo boards

Author: emilmont

libraries/mbed/targets/hal/TARGET_STM/TARGET_NUCLEO_F030R8/us_ticker.c

@@ -36,7 +36,7 @@
 #define TIM_MST_RCC        RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM1, ENABLE)
 
 static int      us_ticker_inited = 0;
-static uint32_t SlaveCounter = 0;
+static volatile uint32_t SlaveCounter = 0;
 static uint32_t oc_int_part = 0;
 static uint16_t oc_rem_part = 0;
 

libraries/mbed/targets/hal/TARGET_STM/TARGET_NUCLEO_F103RB/us_ticker.c

@@ -36,7 +36,7 @@
 #define TIM_MST_RCC        RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM1, ENABLE)
 
 static int      us_ticker_inited = 0;
-static uint32_t SlaveCounter = 0;
+static volatile uint32_t SlaveCounter = 0;
 static uint32_t oc_int_part = 0;
 static uint16_t oc_rem_part = 0;
 

libraries/mbed/targets/hal/TARGET_STM/TARGET_NUCLEO_F401RE/us_ticker.c

@@ -39,7 +39,7 @@
 static TIM_HandleTypeDef TimMasterHandle;
 
 static int      us_ticker_inited = 0;
-static uint32_t SlaveCounter = 0;
+static volatile uint32_t SlaveCounter = 0;
 static uint32_t oc_int_part = 0;
 static uint16_t oc_rem_part = 0;
 

libraries/mbed/targets/hal/TARGET_STM/TARGET_NUCLEO_L152RE/us_ticker.c

@@ -35,7 +35,7 @@
 #define TIM_MST_RCC        RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM9, ENABLE)
 
 static int      us_ticker_inited = 0;
-static uint32_t SlaveCounter = 0;
+static volatile uint32_t SlaveCounter = 0;
 static uint32_t oc_int_part = 0;
 static uint16_t oc_rem_part = 0;