STM32: CAN: restore registers after can_reset

After reset the MCR register content needs to be restored so we're
introducing the can_registers_init function to be called at the first
init stage, but also after reset. We also store the can frequency to
go through the initialisation phase again.

Author: LMESTM

targets/TARGET_STM/TARGET_STM32F0/common_objects.h

@@ -132,6 +132,7 @@ struct dac_s {
 struct can_s {
     CAN_HandleTypeDef CanHandle;
     int index;
+    int hz;
 };
 #endif
 

targets/TARGET_STM/TARGET_STM32F1/common_objects.h

@@ -120,6 +120,7 @@ struct analogin_s {
 struct can_s {
     CAN_HandleTypeDef CanHandle;
     int index;
+    int hz;
 };
 #endif
 

targets/TARGET_STM/TARGET_STM32F2/objects.h

@@ -139,6 +139,7 @@ struct pwmout_s {
 struct can_s {
     CAN_HandleTypeDef CanHandle;
     int index;
+    int hz;
 };
 
 #define GPIO_IP_WITHOUT_BRR

targets/TARGET_STM/TARGET_STM32F3/common_objects.h

@@ -128,6 +128,7 @@ struct analogin_s {
 struct can_s {
     CAN_HandleTypeDef CanHandle;
     int index;
+    int hz;
 };
 #endif
 

targets/TARGET_STM/TARGET_STM32F4/common_objects.h

@@ -137,6 +137,7 @@ struct dac_s {
 struct can_s {
     CAN_HandleTypeDef CanHandle;
     int index;
+    int hz;
 };
 #endif
 

targets/TARGET_STM/TARGET_STM32F7/common_objects.h

@@ -136,6 +136,7 @@ struct flash_s {
 struct can_s {
     CAN_HandleTypeDef CanHandle;
     int index;
+    int hz;
 };
 #endif
 

targets/TARGET_STM/TARGET_STM32L4/common_objects.h

@@ -139,6 +139,7 @@ struct dac_s {
 struct can_s {
     CAN_HandleTypeDef CanHandle;
     int index;
+    int hz;
 };
 #endif
 

targets/TARGET_STM/can_api.c

@@ -28,6 +28,18 @@
 static uint32_t can_irq_ids[CAN_NUM] = {0};
 static can_irq_handler irq_handler;
 
+static void can_registers_init(can_t *obj)
+{
+    if (HAL_CAN_Init(&obj->CanHandle) != HAL_OK) {
+        error("Cannot initialize CAN");
+    }
+
+    // Set initial CAN frequency to specified frequency
+    if (can_frequency(obj, obj->hz) != 1) {
+        error("Can frequency could not be set\n");
+    }
+}
+
 void can_init(can_t *obj, PinName rd, PinName td)
 {
     can_init_freq(obj, rd, td, 100000);
@@ -66,8 +78,8 @@ void can_init_freq (can_t *obj, PinName rd, PinName td, int hz)
         pin_mode(td, PullUp);
     }
 
+    /*  Use default values for rist init */
     obj->CanHandle.Instance = (CAN_TypeDef *)can;
-
     obj->CanHandle.Init.TTCM = DISABLE;
     obj->CanHandle.Init.ABOM = DISABLE;
     obj->CanHandle.Init.AWUM = DISABLE;
@@ -80,19 +92,16 @@ void can_init_freq (can_t *obj, PinName rd, PinName td, int hz)
     obj->CanHandle.Init.BS2 = CAN_BS2_8TQ;
     obj->CanHandle.Init.Prescaler = 2;
 
-    if (HAL_CAN_Init(&obj->CanHandle) != HAL_OK) {
-        error("Cannot initialize CAN");
-    }
+    /*  Store frequency to be restored in case of reset */
+    obj->hz = hz;
 
-    // Set initial CAN frequency to specified frequency
-    if (can_frequency(obj, hz) != 1) {
-        error("Can frequency could not be set\n");
-    }
+    can_registers_init(obj);
 
     uint32_t filter_number = (can == CAN_1) ? 0 : 14;
     can_filter(obj, 0, 0, CANStandard, filter_number);
 }
 
+
 void can_irq_init(can_t *obj, can_irq_handler handler, uint32_t id)
 {
     irq_handler = handler;
@@ -329,8 +338,13 @@ int can_read(can_t *obj, CAN_Message *msg, int handle)
 void can_reset(can_t *obj)
 {
     CAN_TypeDef *can = obj->CanHandle.Instance;
+
+    /* Reset IP and delete errors */
     can->MCR |= CAN_MCR_RESET;
     can->ESR = 0x0;
+
+    /* restore registers state as saved in obj context */
+    can_registers_init(obj);
 }
 
 unsigned char can_rderror(can_t *obj)