drivers: fix attach sleep locking

attach/detach can be multiple invoked. Therefore lock/unlock deep sleep
only for the very first time it is invoked (when callbacks
are actually changed).

drivers/CAN.cpp

@@ -123,7 +123,10 @@ void CAN::attach(Callback<void()> func, IrqType type) {
         _irq[(CanIrqType)type] = func;
         can_irq_set(&_can, (CanIrqType)type, 1);
     } else {
-        sleep_manager_unlock_deep_sleep();
+        // unlock deep sleep only the first time
+        if (_irq[(CanIrqType)type] != callback(donothing)) {
+            sleep_manager_unlock_deep_sleep();
+        }
         _irq[(CanIrqType)type] = callback(donothing);
         can_irq_set(&_can, (CanIrqType)type, 0);
     }

drivers/I2C.cpp

@@ -129,11 +129,11 @@ void I2C::unlock() {
 int I2C::transfer(int address, const char *tx_buffer, int tx_length, char *rx_buffer, int rx_length, const event_callback_t& callback, int event, bool repeated)
 {
     lock();
-    sleep_manager_lock_deep_sleep();
     if (i2c_active(&_i2c)) {
         unlock();
         return -1; // transaction ongoing
     }
+    sleep_manager_lock_deep_sleep();
     aquire();
 
     _callback = callback;

drivers/SerialBase.cpp

@@ -84,7 +84,10 @@ void SerialBase::attach(Callback<void()> func, IrqType type) {
         _irq[type] = func;
         serial_irq_set(&_serial, (SerialIrq)type, 1);
     } else {
-        sleep_manager_unlock_deep_sleep();
+        // unlock deep sleep only the first time
+        if (_irq[type] != donothing) {
+            sleep_manager_unlock_deep_sleep();
+        } 
         _irq[type] = donothing;
         serial_irq_set(&_serial, (SerialIrq)type, 0);
     }
@@ -248,6 +251,7 @@ void SerialBase::start_read(void *buffer, int buffer_size, char buffer_width, co
 {
     _rx_callback = callback;
     _thunk_irq.callback(&SerialBase::interrupt_handler_asynch);
+    sleep_manager_lock_deep_sleep();
     serial_rx_asynch(&_serial, buffer, buffer_size, buffer_width, _thunk_irq.entry(), event, char_match, _rx_usage);
 }