optimized runtime for TXC custom function

optimized runtime for TXC custom function

Author: gicking

Diff for: cores/arduino/HardwareSerial.cpp

@@ -79,6 +79,9 @@ void serialEventRun(void)
 #endif
 }
 
+// dummy function attached to TxC interrupt. Is faster than if(NULL) check 
+void dummyFct(void) { /* dummy */}
+
 // macro to guard critical sections when needed for large TX buffer sizes
 #if (SERIAL_TX_BUFFER_SIZE>256)
 #define TX_BUFFER_ATOMIC ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
@@ -114,15 +117,6 @@ void HardwareSerial::_tx_udr_empty_irq(void)
   }
 }
 
-void HardwareSerial::_tx_complete_irq(void)
-{
-  // user send function was attached -> call it
-  if (_isrTx) {
-    _isrTx();
-  }
-
-}
-
 // Public Methods //////////////////////////////////////////////////////////////
 
 void HardwareSerial::begin(unsigned long baud, byte config)
@@ -158,6 +152,7 @@ void HardwareSerial::begin(unsigned long baud, byte config)
   sbi(*_ucsrb, TXEN0);
   sbi(*_ucsrb, RXCIE0);
   cbi(*_ucsrb, UDRIE0);
+  //cbi(*_ucsrb, TXCIE0);
 }
 
 void HardwareSerial::end()
@@ -300,20 +295,19 @@ void HardwareSerial::attachInterrupt_Receive( isrRx_t fn )
 
 void HardwareSerial::attachInterrupt_Send( isrTx_t fn )
 {
-  uint8_t oldSREG = SREG;
-  cli();
-  _isrTx = fn;
-  sbi(*_ucsrb, TXCIE0);
-  SREG = oldSREG;
+  ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
+    _isrTx = fn;
+    sbi(*_ucsra, TXC0);      // clear TXC status
+    sbi(*_ucsrb, TXCIE0);    // activate TXC interrupt
+  }
 }
 
 void HardwareSerial::detachInterrupt_Send()
 {
-  uint8_t oldSREG = SREG;
-  cli();
-  _isrTx = NULL;
-  cbi(*_ucsrb, TXCIE0);
-  SREG = oldSREG;
+  ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
+    _isrTx = NULL;
+    cbi(*_ucsrb, TXCIE0);    // deactivate TXC interrupt
+  }
 }
 
 #endif // whole file

Diff for: cores/arduino/HardwareSerial.h

@@ -114,6 +114,12 @@ class HardwareSerial : public Stream
     // instruction.
     unsigned char _rx_buffer[SERIAL_RX_BUFFER_SIZE];
     unsigned char _tx_buffer[SERIAL_TX_BUFFER_SIZE];
+    
+    // custom handlers for RX and TXC interrupts 
+    typedef void (* isrRx_t)( uint8_t d, uint8_t s );
+    typedef void (* isrTx_t)( void );
+    isrRx_t  _isrRx;
+    isrTx_t  _isrTx;
 
   public:
     inline HardwareSerial(
@@ -139,17 +145,15 @@ class HardwareSerial : public Stream
     // Interrupt handlers - Not intended to be called externally
     inline void _rx_complete_irq(void);
     void _tx_udr_empty_irq(void);
-    void _tx_complete_irq(void);
+    inline void _tx_complete_irq(void);
 
-    typedef void (* isrRx_t)( uint8_t d, uint8_t s );
+    // attach custom handlers for RX and TXC interrupts 
     void attachInterrupt_Receive( isrRx_t fn );
     void detachInterrupt_Receive() { attachInterrupt_Receive( (isrRx_t) NULL ); };
-    typedef void (* isrTx_t)( void );
     void attachInterrupt_Send( isrTx_t fn );
     void detachInterrupt_Send( void );
+
   private:
-    isrRx_t  _isrRx;
-    isrTx_t  _isrTx;
 
     HardwareSerial( const HardwareSerial & );
     HardwareSerial & operator =( const HardwareSerial &);

Diff for: cores/arduino/HardwareSerial_private.h

@@ -84,6 +84,9 @@
 #error "Not all bit positions for UART3 are the same as for UART0"
 #endif
 
+// dummy custom function attached and TXC interrupt. Is faster than if(NULL) check 
+void dummyFct(void);
+
 // Constructors ////////////////////////////////////////////////////////////////
 
 HardwareSerial::HardwareSerial(
@@ -95,7 +98,7 @@ HardwareSerial::HardwareSerial(
     _udr(udr),
     _rx_buffer_head(0), _rx_buffer_tail(0),
     _tx_buffer_head(0), _tx_buffer_tail(0),
-    _isrRx(0), _isrTx(0)
+    _isrRx(dummyFct), _isrTx(dummyFct)
 {
 }
 
@@ -134,4 +137,10 @@ void HardwareSerial::_rx_complete_irq(void)
   }
 }
 
+void HardwareSerial::_tx_complete_irq(void)
+{
+  // user send function was attached -> call it
+  _isrTx();
+}
+
 #endif // whole file