AP_SLCANIface: prevent hardfault on arm

libraries/AP_CANManager/AP_SLCANIface.cpp

@@ -287,7 +287,7 @@ bool SLCAN::CANIface::init_passthrough(uint8_t i)
  */
 int16_t SLCAN::CANIface::reportFrame(const AP_HAL::CANFrame& frame, uint64_t timestamp_usec)
 {
-    if (_port == nullptr) {
+    if (!is_enabled()) {
         return -1;
     }
 #if HAL_CANFD_SUPPORTED
@@ -377,7 +377,7 @@ int16_t SLCAN::CANIface::reportFrame(const AP_HAL::CANFrame& frame, uint64_t tim
 const char* SLCAN::CANIface::processCommand(char* cmd)
 {
 
-    if (_port == nullptr) {
+    if (!is_enabled()) {
         return nullptr;
     }
 
@@ -461,7 +461,7 @@ const char* SLCAN::CANIface::processCommand(char* cmd)
 // add bytes to parse the received SLCAN Data stream
 inline void SLCAN::CANIface::addByte(const uint8_t byte)
 {
-    if (_port == nullptr) {
+    if (!is_enabled()) {
         return;
     }
     if ((byte >= 32 && byte <= 126)) {  // Normal printable ASCII character
@@ -497,18 +497,20 @@ void SLCAN::CANIface::update_slcan_port()
 {
     const bool armed = hal.util->get_soft_armed();
     if (_set_by_sermgr) {
-        if (armed && _port != nullptr) {
+        if (armed && is_enabled()) {
             // auto-disable when armed
             _port->lock_port(0, 0);
-            _port = nullptr;
+            _enabled = false;
             _set_by_sermgr = false;
         }
         return;
     }
-    if (_port == nullptr && !armed) {
-         _port = AP::serialmanager().find_serial(AP_SerialManager::SerialProtocol_SLCAN, 0);
-        if (_port != nullptr) {
+    if (!is_enabled() && !armed) {
+        auto new_port = AP::serialmanager().find_serial(AP_SerialManager::SerialProtocol_SLCAN, 0);
+        if (new_port != nullptr) {
+            _port = new_port;
             _port->lock_port(_serial_lock_key, _serial_lock_key);
+            _enabled = true;
             _set_by_sermgr = true;
             return;
         }
@@ -521,23 +523,25 @@ void SLCAN::CANIface::update_slcan_port()
         if (((AP_HAL::millis() - _slcan_start_req_time) < ((uint32_t)_slcan_start_delay*1000))) {
             return;
         }
-        _port = AP::serialmanager().get_serial_by_id(_slcan_ser_port);
-        if (_port == nullptr) {
+        auto new_port = AP::serialmanager().get_serial_by_id(_slcan_ser_port);
+        if (new_port == nullptr) {
             _slcan_ser_port.set_and_save(-1);
             return;
         }
+        _port = new_port;
         _port->lock_port(_serial_lock_key, _serial_lock_key);
+        _enabled = true;
         _prev_ser_port = _slcan_ser_port;
         GCS_SEND_TEXT(MAV_SEVERITY_INFO, "CANManager: Starting SLCAN Passthrough on Serial %d with CAN%d", _slcan_ser_port.get(), _iface_num);
         _last_had_activity = AP_HAL::millis();
     }
-    if (_port == nullptr) {
+    if (!is_enabled()) {
         return;
     }
     if (((AP_HAL::millis() - _last_had_activity) > ((uint32_t)_slcan_timeout*1000)) &&
         (uint32_t)_slcan_timeout != 0) {
         _port->lock_port(0, 0);
-        _port = nullptr;
+        _enabled = false;
         _slcan_ser_port.set_and_save(-1);
         _prev_ser_port = -1;
         _slcan_start_req = false;
@@ -637,7 +641,7 @@ bool SLCAN::CANIface::select(bool &read, bool &write, const AP_HAL::CANFrame* co
         ret = _can_iface->select(read, write, pending_tx, blocking_deadline);
     }
 
-    if (_port == nullptr) {
+    if (!is_enabled()) {
         return ret;
     }
 
@@ -665,7 +669,7 @@ int16_t SLCAN::CANIface::send(const AP_HAL::CANFrame& frame, uint64_t tx_deadlin
         ret = _can_iface->send(frame, tx_deadline, flags);
     }
 
-    if (_port == nullptr) {
+    if (!is_enabled()) {
         return ret;
     }
 
@@ -699,7 +703,7 @@ int16_t SLCAN::CANIface::receive(AP_HAL::CANFrame& out_frame, uint64_t& rx_time,
     }
 
     // We found nothing in HAL's CANIface receive, so look in SLCANIface
-    if (_port == nullptr) {
+    if (!is_enabled()) {
         return 0;
     }
 

libraries/AP_CANManager/AP_SLCANIface.h

@@ -67,6 +67,7 @@ class CANIface: public AP_HAL::CANIface
     char buf_[SLCAN_BUFFER_SIZE + 1]; // buffer to record raw frame nibbles before parsing
     int16_t pos_ = 0; // position in the buffer recording nibble frames before parsing
     AP_HAL::UARTDriver* _port; // UART interface port reference to be used for SLCAN iface
+    bool _enabled; // Flag to check whether we are allowed to use _port
 
     ObjectBuffer<AP_HAL::CANIface::CanRxItem> rx_queue_; // Parsed Rx Frame queue
 
@@ -137,6 +138,9 @@ class CANIface: public AP_HAL::CANIface
     bool add_to_rx_queue(const AP_HAL::CANIface::CanRxItem &frm) override {
         return rx_queue_.push(frm);
     }
+    bool is_enabled() const {
+        return (_port != nullptr) && _enabled;
+    }
 };
 
 }