From 3a9c98967663f8cd57239e9b16684830921fa18d Mon Sep 17 00:00:00 2001
From: Matthijs Kooijman <matthijs@stdin.nl>
Date: Fri, 19 Apr 2013 15:29:43 +0200
Subject: [PATCH 01/15] Remove duplicate code from HardwareSerial::begin()
 methods.

There are two begin methods, one which accepts just a baud rate and
uses the default bit settings and one which accepts both a baudrate and
a bit config. Previously, both of these contained a complete
implementation, but now the former just calls the latter, explicitely
passing the default 8N1 configuration.

Technically, this causes a small change: Before the UCSRC register was
untouched when calling begin(baud), now it is explicitely initialized
with 8N1. However, since this is the default configuration for at least
the Uno and the Mega (didn't check any others), probably for all avrs,
this shouldn't effectively change anything. Given that the Arduino
documentation also documents this as the default when none is passed,
explicitly setting it is probably a good idea in any case.
---
 .../avr/cores/arduino/HardwareSerial.cpp      | 39 +------------------
 1 file changed, 1 insertion(+), 38 deletions(-)

diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
index 9a86fa069d0..f95fa5d4ba3 100644
--- a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
@@ -283,44 +283,7 @@ HardwareSerial::HardwareSerial(
 
 void HardwareSerial::begin(unsigned long baud)
 {
-  uint16_t baud_setting;
-  bool use_u2x = true;
-
-#if F_CPU == 16000000UL
-  // hardcoded exception for compatibility with the bootloader shipped
-  // with the Duemilanove and previous boards and the firmware on the 8U2
-  // on the Uno and Mega 2560.
-  if (baud == 57600) {
-    use_u2x = false;
-  }
-#endif
-
-try_again:
-  
-  if (use_u2x) {
-    *_ucsra = 1 << _u2x;
-    baud_setting = (F_CPU / 4 / baud - 1) / 2;
-  } else {
-    *_ucsra = 0;
-    baud_setting = (F_CPU / 8 / baud - 1) / 2;
-  }
-  
-  if ((baud_setting > 4095) && use_u2x)
-  {
-    use_u2x = false;
-    goto try_again;
-  }
-
-  // assign the baud_setting, a.k.a. ubbr (USART Baud Rate Register)
-  *_ubrrh = baud_setting >> 8;
-  *_ubrrl = baud_setting;
-
-  transmitting = false;
-
-  sbi(*_ucsrb, _rxen);
-  sbi(*_ucsrb, _txen);
-  sbi(*_ucsrb, _rxcie);
-  cbi(*_ucsrb, _udrie);
+  begin(baud, SERIAL_8N1);
 }
 
 void HardwareSerial::begin(unsigned long baud, byte config)

From 43c65f44d68806e1cc71d1bab3c73b184b7dfc52 Mon Sep 17 00:00:00 2001
From: Matthijs Kooijman <matthijs@stdin.nl>
Date: Fri, 19 Apr 2013 16:12:31 +0200
Subject: [PATCH 02/15] Remove unused variable

---
 hardware/arduino/avr/cores/arduino/HardwareSerial.cpp | 1 -
 1 file changed, 1 deletion(-)

diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
index f95fa5d4ba3..be1732e1c98 100644
--- a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
@@ -289,7 +289,6 @@ void HardwareSerial::begin(unsigned long baud)
 void HardwareSerial::begin(unsigned long baud, byte config)
 {
   uint16_t baud_setting;
-  uint8_t current_config;
   bool use_u2x = true;
 
 #if F_CPU == 16000000UL

From a2fa47bdc980e65b878ab37db7ec6961810d0f05 Mon Sep 17 00:00:00 2001
From: Matthijs Kooijman <matthijs@stdin.nl>
Date: Fri, 19 Apr 2013 16:32:33 +0200
Subject: [PATCH 03/15] Simplify HardwareSerial::begin()

This simplifies the baud rate calculation, removing the need for a goto
and shortening the code a bit. Other than that, this code should not use
any different settings than before.

Code was suggested by Rob Tillaart on github.

Closes: #1262
---
 .../avr/cores/arduino/HardwareSerial.cpp      | 35 ++++++-------------
 1 file changed, 11 insertions(+), 24 deletions(-)

diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
index be1732e1c98..7fcab974d8d 100644
--- a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
@@ -288,33 +288,20 @@ void HardwareSerial::begin(unsigned long baud)
 
 void HardwareSerial::begin(unsigned long baud, byte config)
 {
-  uint16_t baud_setting;
-  bool use_u2x = true;
-
-#if F_CPU == 16000000UL
-  // hardcoded exception for compatibility with the bootloader shipped
-  // with the Duemilanove and previous boards and the firmware on the 8U2
-  // on the Uno and Mega 2560.
-  if (baud == 57600) {
-    use_u2x = false;
-  }
-#endif
-
-try_again:
-  
-  if (use_u2x) {
-    *_ucsra = 1 << _u2x;
-    baud_setting = (F_CPU / 4 / baud - 1) / 2;
-  } else {
+  // Try u2x mode first
+  uint16_t baud_setting = (F_CPU / 4 / baud - 1) / 2;
+  *_ucsra = 1 << _u2x;
+
+  // hardcoded exception for 57600 for compatibility with the bootloader
+  // shipped with the Duemilanove and previous boards and the firmware
+  // on the 8U2 on the Uno and Mega 2560. Also, The baud_setting cannot
+  // be > 4095, so switch back to non-u2x mode if the baud rate is too
+  // low.
+  if (((F_CPU == 16000000UL) && (baud == 57600)) || (baud_setting >4095))
+  {
     *_ucsra = 0;
     baud_setting = (F_CPU / 8 / baud - 1) / 2;
   }
-  
-  if ((baud_setting > 4095) && use_u2x)
-  {
-    use_u2x = false;
-    goto try_again;
-  }
 
   // assign the baud_setting, a.k.a. ubbr (USART Baud Rate Register)
   *_ubrrh = baud_setting >> 8;

From 193bb9ab93ddc2337de188f09587960cc3f67269 Mon Sep 17 00:00:00 2001
From: Matthijs Kooijman <matthijs@stdin.nl>
Date: Sun, 1 Dec 2013 19:18:31 +0100
Subject: [PATCH 04/15] Define a _NOP() macro

Recent avr-libc releases define one, but this allows using it also on
older avr-libc releases.
---
 hardware/arduino/avr/cores/arduino/Arduino.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/hardware/arduino/avr/cores/arduino/Arduino.h b/hardware/arduino/avr/cores/arduino/Arduino.h
index de1886d5dde..3f125bc4c92 100644
--- a/hardware/arduino/avr/cores/arduino/Arduino.h
+++ b/hardware/arduino/avr/cores/arduino/Arduino.h
@@ -87,6 +87,10 @@ void yield(void);
 #define bitClear(value, bit) ((value) &= ~(1UL << (bit)))
 #define bitWrite(value, bit, bitvalue) (bitvalue ? bitSet(value, bit) : bitClear(value, bit))
 
+// avr-libc defines _NOP() since 1.6.2
+#ifndef _NOP
+#define _NOP() do { __asm__ volatile ("nop"); } while (0)
+#endif
 
 typedef unsigned int word;
 

From b99521de0c3bcc9f1be96a8fb955a8d84ff89ad5 Mon Sep 17 00:00:00 2001
From: Matthijs Kooijman <matthijs@stdin.nl>
Date: Thu, 18 Apr 2013 14:17:47 +0200
Subject: [PATCH 05/15] Use constants for register bit positions in
 HardwareSerial

Previously, the constants to use for the bit positions of the various
UARTs were passed to the HardwareSerial constructor. However, this
meant that whenever these values were used, the had to be indirectly
loaded, resulting in extra code overhead. Additionally, since there is
no instruction to shift a value by a variable amount, the 1 << x
expressions (inside _BV and sbi() / cbi()) would be compiled as a loop
instead of being evaluated at compiletime.

Now, the HardwareSerial class always uses the constants for the bit
positions of UART 0 (and some code is present to make sure these
constants exist, even for targets that only have a single unnumbered
UART or start at UART1).

This was already done for the TXC0 constant, for some reason. For the
actual register addresses, this approach does not work, since these are
of course different between the different UARTs on a single chip.

Of course, always using the UART 0 constants is only correct when the
constants are actually identical for the different UARTs. It has been
verified that this is currently the case for all targets supported by
avr-gcc 4.7.2, and the code contains compile-time checks to verify this
for the current target, in case a new target is added for which this
does not hold. This verification was done using:

for i in TXC RXEN TXEN RXCIE UDRIE U2X UPE; do echo $i; grep --no-filename -r "#define $i[0-9]\? " /usr/lib/avr/include/avr/io* | sed "s/#define $i[0-9]\?\s*\(\S\)\+\s*\(\/\*.*\*\/\)\?$/\1/" | sort | uniq ; done

This command shows that the above constants are identical for all uarts
on all platforms, except for TXC, which is sometimes 6 and sometimes 0.
Further investigation shows that it is always 6, except in io90scr100.h,
but that file defines TXC0 with value 6 for the UART and uses TXC with
value 0 for some USB-related register.

This commit reduces program size on the uno by around 120 bytes.
---
 .../avr/cores/arduino/HardwareSerial.cpp      | 83 +++++++++++++------
 .../avr/cores/arduino/HardwareSerial.h        |  8 +-
 2 files changed, 57 insertions(+), 34 deletions(-)

diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
index 7fcab974d8d..6ce8b915648 100644
--- a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
@@ -34,19 +34,54 @@
 
 #include "HardwareSerial.h"
 
-/*
- * on ATmega8, the uart and its bits are not numbered, so there is no "TXC0"
- * definition.
- */
+// Ensure that the various bit positions we use are available with a 0
+// postfix, so we can always use the values for UART0 for all UARTs. The
+// alternative, passing the various values for each UART to the
+// HardwareSerial constructor also works, but makes the code bigger and
+// slower.
 #if !defined(TXC0)
 #if defined(TXC)
+// On ATmega8, the uart and its bits are not numbered, so there is no TXC0 etc.
 #define TXC0 TXC
+#define RXEN0 RXEN
+#define TXEN0 TXEN
+#define RXCIE0 RXCIE
+#define UDRIE0 UDRIE
+#define U2X0 U2X
+#define UPE0 UPE
+#define UDRE0 UDRE
 #elif defined(TXC1)
 // Some devices have uart1 but no uart0
 #define TXC0 TXC1
+#define RXEN0 RXEN1
+#define TXEN0 TXEN1
+#define RXCIE0 RXCIE1
+#define UDRIE0 UDRIE1
+#define U2X0 U2X1
+#define UPE0 UPE1
+#define UDRE0 UDRE1
 #else
-#error TXC0 not definable in HardwareSerial.h
+#error No UART found in HardwareSerial.cpp
+#endif
+#endif // !defined TXC0
+
+// Check at compiletime that it is really ok to use the bit positions of
+// UART0 for the other UARTs as well, in case these values ever get
+// changed for future hardware.
+#if defined(TXC1) && (TXC1 != TXC0 || RXEN1 != RXEN0 || RXCIE1 != RXCIE0 || \
+		      UDRIE1 != UDRIE0 || U2X1 != U2X0 || UPE1 != UPE0 || \
+		      UDRE1 != UDRE0)
+#error "Not all bit positions for UART1 are the same as for UART0"
+#endif
+#if defined(TXC2) && (TXC2 != TXC0 || RXEN2 != RXEN0 || RXCIE2 != RXCIE0 || \
+		      UDRIE2 != UDRIE0 || U2X2 != U2X0 || UPE2 != UPE0 || \
+		      UDRE2 != UDRE0)
+#error "Not all bit positions for UART2 are the same as for UART0"
 #endif
+#if defined(TXC3) && (TXC3 != TXC0 || RXEN3 != RXEN0 || RXCIE3 != RXCIE0 || \
+		      UDRIE3 != UDRIE0 || U3X3 != U3X0 || UPE3 != UPE0 || \
+		      UDRE3 != UDRE0)
+#error "Not all bit positions for UART3 are the same as for UART0"
 #endif
 
 inline void store_char(unsigned char c, HardwareSerial *s)
@@ -261,8 +296,7 @@ ISR(USART3_UDRE_vect)
 HardwareSerial::HardwareSerial(
   volatile uint8_t *ubrrh, volatile uint8_t *ubrrl,
   volatile uint8_t *ucsra, volatile uint8_t *ucsrb,
-  volatile uint8_t *ucsrc, volatile uint8_t *udr,
-  uint8_t rxen, uint8_t txen, uint8_t rxcie, uint8_t udrie, uint8_t u2x)
+  volatile uint8_t *ucsrc, volatile uint8_t *udr)
 {
   _tx_buffer_head = _tx_buffer_tail = 0;
   _rx_buffer_head = _rx_buffer_tail = 0;
@@ -272,11 +306,6 @@ HardwareSerial::HardwareSerial(
   _ucsrb = ucsrb;
   _ucsrc = ucsrc;
   _udr = udr;
-  _rxen = rxen;
-  _txen = txen;
-  _rxcie = rxcie;
-  _udrie = udrie;
-  _u2x = u2x;
 }
 
 // Public Methods //////////////////////////////////////////////////////////////
@@ -290,7 +319,7 @@ void HardwareSerial::begin(unsigned long baud, byte config)
 {
   // Try u2x mode first
   uint16_t baud_setting = (F_CPU / 4 / baud - 1) / 2;
-  *_ucsra = 1 << _u2x;
+  *_ucsra = 1 << U2X0;
 
   // hardcoded exception for 57600 for compatibility with the bootloader
   // shipped with the Duemilanove and previous boards and the firmware
@@ -313,10 +342,10 @@ void HardwareSerial::begin(unsigned long baud, byte config)
 #endif
   *_ucsrc = config;
   
-  sbi(*_ucsrb, _rxen);
-  sbi(*_ucsrb, _txen);
-  sbi(*_ucsrb, _rxcie);
-  cbi(*_ucsrb, _udrie);
+  sbi(*_ucsrb, RXEN0);
+  sbi(*_ucsrb, TXEN0);
+  sbi(*_ucsrb, RXCIE0);
+  cbi(*_ucsrb, UDRIE0);
 }
 
 void HardwareSerial::end()
@@ -325,10 +354,10 @@ void HardwareSerial::end()
   while (_tx_buffer_head != _tx_buffer_tail)
     ;
 
-  cbi(*_ucsrb, _rxen);
-  cbi(*_ucsrb, _txen);
-  cbi(*_ucsrb, _rxcie);  
-  cbi(*_ucsrb, _udrie);
+  cbi(*_ucsrb, RXEN0);
+  cbi(*_ucsrb, TXEN0);
+  cbi(*_ucsrb, RXCIE0);
+  cbi(*_ucsrb, UDRIE0);
   
   // clear any received data
   _rx_buffer_head = _rx_buffer_tail;
@@ -380,7 +409,7 @@ size_t HardwareSerial::write(uint8_t c)
   _tx_buffer[_tx_buffer_head] = c;
   _tx_buffer_head = i;
 	
-  sbi(*_ucsrb, _udrie);
+  sbi(*_ucsrb, UDRIE0);
   // clear the TXC bit -- "can be cleared by writing a one to its bit location"
   transmitting = true;
   sbi(*_ucsra, TXC0);
@@ -395,9 +424,9 @@ HardwareSerial::operator bool() {
 // Preinstantiate Objects //////////////////////////////////////////////////////
 
 #if defined(UBRRH) && defined(UBRRL)
-  HardwareSerial Serial(&UBRRH, &UBRRL, &UCSRA, &UCSRB, &UCSRC, &UDR, RXEN, TXEN, RXCIE, UDRIE, U2X);
+  HardwareSerial Serial(&UBRRH, &UBRRL, &UCSRA, &UCSRB, &UCSRC, &UDR);
 #elif defined(UBRR0H) && defined(UBRR0L)
-  HardwareSerial Serial(&UBRR0H, &UBRR0L, &UCSR0A, &UCSR0B, &UCSR0C, &UDR0, RXEN0, TXEN0, RXCIE0, UDRIE0, U2X0);
+  HardwareSerial Serial(&UBRR0H, &UBRR0L, &UCSR0A, &UCSR0B, &UCSR0C, &UDR0);
 #elif defined(USBCON)
   // do nothing - Serial object and buffers are initialized in CDC code
 #else
@@ -405,13 +434,13 @@ HardwareSerial::operator bool() {
 #endif
 
 #if defined(UBRR1H)
-  HardwareSerial Serial1(&UBRR1H, &UBRR1L, &UCSR1A, &UCSR1B, &UCSR1C, &UDR1, RXEN1, TXEN1, RXCIE1, UDRIE1, U2X1);
+  HardwareSerial Serial1(&UBRR1H, &UBRR1L, &UCSR1A, &UCSR1B, &UCSR1C, &UDR1);
 #endif
 #if defined(UBRR2H)
-  HardwareSerial Serial2(&UBRR2H, &UBRR2L, &UCSR2A, &UCSR2B, &UCSR2C, &UDR2, RXEN2, TXEN2, RXCIE2, UDRIE2, U2X2);
+  HardwareSerial Serial2(&UBRR2H, &UBRR2L, &UCSR2A, &UCSR2B, &UCSR2C, &UDR2);
 #endif
 #if defined(UBRR3H)
-  HardwareSerial Serial3(&UBRR3H, &UBRR3L, &UCSR3A, &UCSR3B, &UCSR3C, &UDR3, RXEN3, TXEN3, RXCIE3, UDRIE3, U2X3);
+  HardwareSerial Serial3(&UBRR3H, &UBRR3L, &UCSR3A, &UCSR3B, &UCSR3C, &UDR3);
 #endif
 
 #endif // whole file
diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial.h b/hardware/arduino/avr/cores/arduino/HardwareSerial.h
index 0f622625320..e1b3903e2fc 100644
--- a/hardware/arduino/avr/cores/arduino/HardwareSerial.h
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial.h
@@ -46,11 +46,6 @@ class HardwareSerial : public Stream
     volatile uint8_t *_ucsrb;
     volatile uint8_t *_ucsrc;
     volatile uint8_t *_udr;
-    uint8_t _rxen;
-    uint8_t _txen;
-    uint8_t _rxcie;
-    uint8_t _udrie;
-    uint8_t _u2x;
     bool transmitting;
 
   public:
@@ -68,8 +63,7 @@ class HardwareSerial : public Stream
     HardwareSerial(
       volatile uint8_t *ubrrh, volatile uint8_t *ubrrl,
       volatile uint8_t *ucsra, volatile uint8_t *ucsrb,
-      volatile uint8_t *ucsrc, volatile uint8_t *udr,
-      uint8_t rxen, uint8_t txen, uint8_t rxcie, uint8_t udrie, uint8_t u2x);
+      volatile uint8_t *ucsrc, volatile uint8_t *udr);
     void begin(unsigned long);
     void begin(unsigned long, uint8_t);
     void end();

From 91a405c7b4d8854fb0fa3d50d7a49ae34443bbac Mon Sep 17 00:00:00 2001
From: Matthijs Kooijman <matthijs@stdin.nl>
Date: Thu, 18 Apr 2013 11:38:13 +0200
Subject: [PATCH 06/15] Move interrupt handlers into HardwareSerial class

The actual interrupt vectors are of course defined as before, but they
let new methods in the HardwareSerial class do the actual work. This
greatly reduces code duplication and prepares for one of my next commits
which requires the tx interrupt handler to be called from another
context as well.

The actual content of the interrupts handlers was pretty much identical,
so that remains unchanged (except that store_char was now only needed
once, so it was inlined).

Now all access to the buffers are inside the HardwareSerial class, the
buffer variables can be made private.

One would expect a program size reduction from this change (at least
with multiple UARTs), but due to the fact that the interrupt handlers
now only have indirect access to a few registers (which previously were
just hardcoded in the handlers) and because there is some extra function
call overhead, the code size on the uno actually increases by around
70 bytes. On the mega, which has four UARTs, the code size decreases by
around 70 bytes.
---
 .../avr/cores/arduino/HardwareSerial.cpp      | 145 ++++++------------
 .../avr/cores/arduino/HardwareSerial.h        |   6 +-
 2 files changed, 50 insertions(+), 101 deletions(-)

diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
index 6ce8b915648..7a5a1412ba1 100644
--- a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
@@ -84,20 +84,6 @@
 #error "Not all bit positions for UART3 are the same as for UART0"
 #endif
 
-inline void store_char(unsigned char c, HardwareSerial *s)
-{
-  int i = (unsigned int)(s->_rx_buffer_head + 1) % SERIAL_BUFFER_SIZE;
-
-  // if we should be storing the received character into the location
-  // just before the tail (meaning that the head would advance to the
-  // current location of the tail), we're about to overflow the buffer
-  // and so we don't write the character or advance the head.
-  if (i != s->_rx_buffer_tail) {
-    s->_rx_buffer[s->_rx_buffer_head] = c;
-    s->_rx_buffer_head = i;
-  }
-}
-
 #if !defined(USART0_RX_vect) && defined(USART1_RX_vect)
 // do nothing - on the 32u4 the first USART is USART1
 #else
@@ -116,23 +102,7 @@ inline void store_char(unsigned char c, HardwareSerial *s)
   ISR(USART_RXC_vect) // ATmega8
 #endif
   {
-  #if defined(UDR0)
-    if (bit_is_clear(UCSR0A, UPE0)) {
-      unsigned char c = UDR0;
-      store_char(c, &Serial);
-    } else {
-      unsigned char c = UDR0;
-    };
-  #elif defined(UDR)
-    if (bit_is_clear(UCSRA, PE)) {
-      unsigned char c = UDR;
-      store_char(c, &Serial);
-    } else {
-      unsigned char c = UDR;
-    };
-  #else
-    #error UDR not defined
-  #endif
+    Serial._rx_complete_irq();
   }
 #endif
 #endif
@@ -143,12 +113,7 @@ inline void store_char(unsigned char c, HardwareSerial *s)
   #define serialEvent1_implemented
   ISR(USART1_RX_vect)
   {
-    if (bit_is_clear(UCSR1A, UPE1)) {
-      unsigned char c = UDR1;
-      store_char(c, &Serial1);
-    } else {
-      unsigned char c = UDR1;
-    };
+    Serial1._rx_complete_irq();
   }
 #endif
 
@@ -158,12 +123,7 @@ inline void store_char(unsigned char c, HardwareSerial *s)
   #define serialEvent2_implemented
   ISR(USART2_RX_vect)
   {
-    if (bit_is_clear(UCSR2A, UPE2)) {
-      unsigned char c = UDR2;
-      store_char(c, &Serial2);
-    } else {
-      unsigned char c = UDR2;
-    };
+    Serial2._rx_complete_irq();
   }
 #endif
 
@@ -173,12 +133,7 @@ inline void store_char(unsigned char c, HardwareSerial *s)
   #define serialEvent3_implemented
   ISR(USART3_RX_vect)
   {
-    if (bit_is_clear(UCSR3A, UPE3)) {
-      unsigned char c = UDR3;
-      store_char(c, &Serial3);
-    } else {
-      unsigned char c = UDR3;
-    };
+    Serial3._rx_complete_irq();
   }
 #endif
 
@@ -215,27 +170,7 @@ ISR(USART0_UDRE_vect)
 ISR(USART_UDRE_vect)
 #endif
 {
-  if (Serial._tx_buffer_head == Serial._tx_buffer_tail) {
-	// Buffer empty, so disable interrupts
-#if defined(UCSR0B)
-    cbi(UCSR0B, UDRIE0);
-#else
-    cbi(UCSRB, UDRIE);
-#endif
-  }
-  else {
-    // There is more data in the output buffer. Send the next byte
-    unsigned char c = Serial._tx_buffer[Serial._tx_buffer_tail];
-    Serial._tx_buffer_tail = (Serial._tx_buffer_tail + 1) % SERIAL_BUFFER_SIZE;
-	
-  #if defined(UDR0)
-    UDR0 = c;
-  #elif defined(UDR)
-    UDR = c;
-  #else
-    #error UDR not defined
-  #endif
-  }
+  Serial._tx_udr_empty_irq();
 }
 #endif
 #endif
@@ -243,53 +178,63 @@ ISR(USART_UDRE_vect)
 #ifdef USART1_UDRE_vect
 ISR(USART1_UDRE_vect)
 {
-  if (Serial1._tx_buffer_head == Serial1._tx_buffer_tail) {
-	// Buffer empty, so disable interrupts
-    cbi(UCSR1B, UDRIE1);
-  }
-  else {
-    // There is more data in the output buffer. Send the next byte
-    unsigned char c = Serial1._tx_buffer[Serial1._tx_buffer_tail];
-    Serial1._tx_buffer_tail = (Serial1._tx_buffer_tail + 1) % SERIAL_BUFFER_SIZE;
-	
-    UDR1 = c;
-  }
+  Serial1._tx_udr_empty_irq();
 }
 #endif
 
 #ifdef USART2_UDRE_vect
 ISR(USART2_UDRE_vect)
 {
-  if (Serial2._tx_buffer_head == Serial2._tx_buffer_tail) {
-	// Buffer empty, so disable interrupts
-    cbi(UCSR2B, UDRIE2);
-  }
-  else {
-    // There is more data in the output buffer. Send the next byte
-    unsigned char c = Serial2._tx_buffer[Serial2._tx_buffer_tail];
-    Serial2._tx_buffer_tail = (Serial2._tx_buffer_tail + 1) % SERIAL_BUFFER_SIZE;
-	
-    UDR2 = c;
-  }
+  Serial2._tx_udr_empty_irq();
 }
 #endif
 
 #ifdef USART3_UDRE_vect
 ISR(USART3_UDRE_vect)
 {
-  if (Serial3._tx_buffer_head == Serial3._tx_buffer_tail) {
-	// Buffer empty, so disable interrupts
-    cbi(UCSR3B, UDRIE3);
+  Serial3._tx_udr_empty_irq();
+}
+#endif
+
+
+// Actual interrupt handlers //////////////////////////////////////////////////////////////
+
+void HardwareSerial::_rx_complete_irq(void)
+{
+  if (bit_is_clear(*_ucsra, UPE0)) {
+    // No Parity error, read byte and store it in the buffer if there is
+    // room
+    unsigned char c = *_udr;
+    int i = (unsigned int)(_rx_buffer_head + 1) % SERIAL_BUFFER_SIZE;
+
+    // if we should be storing the received character into the location
+    // just before the tail (meaning that the head would advance to the
+    // current location of the tail), we're about to overflow the buffer
+    // and so we don't write the character or advance the head.
+    if (i != _rx_buffer_tail) {
+      _rx_buffer[_rx_buffer_head] = c;
+      _rx_buffer_head = i;
+    }
+  } else {
+    // Parity error, read byte but discard it
+    unsigned char c = *_udr;
+  };
+}
+
+void HardwareSerial::_tx_udr_empty_irq(void)
+{
+  if (_tx_buffer_head == _tx_buffer_tail) {
+    // Buffer empty, so disable interrupts
+    cbi(*_ucsrb, UDRIE0);
   }
   else {
     // There is more data in the output buffer. Send the next byte
-    unsigned char c = Serial3._tx_buffer[Serial3._tx_buffer_tail];
-    Serial3._tx_buffer_tail = (Serial3._tx_buffer_tail + 1) % SERIAL_BUFFER_SIZE;
-	
-    UDR3 = c;
+    unsigned char c = _tx_buffer[_tx_buffer_tail];
+    _tx_buffer_tail = (_tx_buffer_tail + 1) % SERIAL_BUFFER_SIZE;
+
+    *_udr = c;
   }
 }
-#endif
 
 // Constructors ////////////////////////////////////////////////////////////////
 
diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial.h b/hardware/arduino/avr/cores/arduino/HardwareSerial.h
index e1b3903e2fc..2dd14099747 100644
--- a/hardware/arduino/avr/cores/arduino/HardwareSerial.h
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial.h
@@ -48,7 +48,6 @@ class HardwareSerial : public Stream
     volatile uint8_t *_udr;
     bool transmitting;
 
-  public:
     volatile uint8_t _rx_buffer_head;
     volatile uint8_t _rx_buffer_tail;
     volatile uint8_t _tx_buffer_head;
@@ -60,6 +59,7 @@ class HardwareSerial : public Stream
     unsigned char _rx_buffer[SERIAL_BUFFER_SIZE];
     unsigned char _tx_buffer[SERIAL_BUFFER_SIZE];
 
+  public:
     HardwareSerial(
       volatile uint8_t *ubrrh, volatile uint8_t *ubrrl,
       volatile uint8_t *ucsra, volatile uint8_t *ucsrb,
@@ -78,6 +78,10 @@ class HardwareSerial : public Stream
     inline size_t write(int n) { return write((uint8_t)n); }
     using Print::write; // pull in write(str) and write(buf, size) from Print
     operator bool();
+
+    // Interrupt handlers - Not intended to be called externally
+    void _rx_complete_irq(void);
+    void _tx_udr_empty_irq(void);
 };
 
 // Define config for Serial.begin(baud, config);

From da984c977c4670a76b0a3d4f4055b7af3f9e98d3 Mon Sep 17 00:00:00 2001
From: Matthijs Kooijman <matthijs@stdin.nl>
Date: Thu, 18 Apr 2013 20:20:03 +0200
Subject: [PATCH 07/15] Use bit_is_clear in HardwareSerial::flush()

This is slightly more clear than the previous explicit comparison.
---
 hardware/arduino/avr/cores/arduino/HardwareSerial.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
index 7a5a1412ba1..f0e11bed2c8 100644
--- a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
@@ -337,7 +337,7 @@ int HardwareSerial::read(void)
 void HardwareSerial::flush()
 {
   // UDR is kept full while the buffer is not empty, so TXC triggers when EMPTY && SENT
-  while (transmitting && ! (*_ucsra & _BV(TXC0)));
+  while (transmitting && bit_is_clear(*_ucsra, TXC0));
   transmitting = false;
 }
 

From 59c6467eb0d4a6cbbefce2d39408ad7f5f60b660 Mon Sep 17 00:00:00 2001
From: Matthijs Kooijman <matthijs@stdin.nl>
Date: Thu, 18 Apr 2013 21:12:01 +0200
Subject: [PATCH 08/15] Improve HardwareSerial::flush()

The flush() method blocks until all characters in the serial buffer have
been written to the uart _and_ transmitted. This is checked by waiting
until the "TXC" (TX Complete) bit is set by the UART, signalling
completion. This bit is cleared by write() when adding a new byte to the
buffer and set by the hardware after tranmission ends, so it is always
guaranteed to be zero from the moment the first byte in a sequence is
queued until the moment the last byte is transmitted, and it is one from
the moment the last byte in the buffer is transmitted until the first
byte in the next sequence is queued.

However, the TXC bit is also zero from initialization to the moment the
first byte ever is queued (and then continues to be zero until the first
sequence of bytes completes transmission). Unfortunately we cannot
manually set the TXC bit during initialization, we can only clear it. To
make sure that flush() would not (indefinitely) block when it is called
_before_ anything was written to the serial device, the "transmitting"
variable was introduced.

This variable suggests that it is only true when something is
transmitting, which isn't currently the case (it remains true after
transmission is complete until flush() is called, for example).
Furthermore, there is no need to keep the status of transmission, the
only thing needed is to remember if anything has ever been written, so
the corner case described above can be detected.

This commit improves the code by:
 - Renaming the "transmitting" variable to _written (making it more
   clear and following the leading underscore naming convention).
 - Not resetting the value of _written at the end of flush(), there is
   no point to this.
 - Only checking the "_written" value once in flush(), since it can
   never be toggled off anyway.
 - Initializing the value of _written in both versions of _begin (though
   it probably gets initialized to 0 by default anyway, better to be
   explicit).
---
 .../avr/cores/arduino/HardwareSerial.cpp      | 20 ++++++++++++++-----
 .../avr/cores/arduino/HardwareSerial.h        |  3 ++-
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
index f0e11bed2c8..6a97cf726ae 100644
--- a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
@@ -281,6 +281,8 @@ void HardwareSerial::begin(unsigned long baud, byte config)
   *_ubrrh = baud_setting >> 8;
   *_ubrrl = baud_setting;
 
+  _written = false;
+
   //set the data bits, parity, and stop bits
 #if defined(__AVR_ATmega8__)
   config |= 0x80; // select UCSRC register (shared with UBRRH)
@@ -336,9 +338,15 @@ int HardwareSerial::read(void)
 
 void HardwareSerial::flush()
 {
-  // UDR is kept full while the buffer is not empty, so TXC triggers when EMPTY && SENT
-  while (transmitting && bit_is_clear(*_ucsra, TXC0));
-  transmitting = false;
+  // If we have never written a byte, no need to flush. This special
+  // case is needed since there is no way to force the TXC (transmit
+  // complete) bit to 1 during initialization
+  if (!_written)
+    return;
+
+  // UDR is kept full while the buffer is not empty, so TXC triggers
+  // when EMPTY && SENT
+  while (bit_is_clear(*_ucsra, TXC0));
 }
 
 size_t HardwareSerial::write(uint8_t c)
@@ -355,8 +363,10 @@ size_t HardwareSerial::write(uint8_t c)
   _tx_buffer_head = i;
 	
   sbi(*_ucsrb, UDRIE0);
-  // clear the TXC bit -- "can be cleared by writing a one to its bit location"
-  transmitting = true;
+  _written = true;
+  // clear the TXC bit -- "can be cleared by writing a one to its bit
+  // location". This makes sure flush() won't return until the bytes
+  // actually got written
   sbi(*_ucsra, TXC0);
   
   return 1;
diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial.h b/hardware/arduino/avr/cores/arduino/HardwareSerial.h
index 2dd14099747..c6649df83a6 100644
--- a/hardware/arduino/avr/cores/arduino/HardwareSerial.h
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial.h
@@ -46,7 +46,8 @@ class HardwareSerial : public Stream
     volatile uint8_t *_ucsrb;
     volatile uint8_t *_ucsrc;
     volatile uint8_t *_udr;
-    bool transmitting;
+    // Has any byte been written to the UART since begin()
+    bool _written;
 
     volatile uint8_t _rx_buffer_head;
     volatile uint8_t _rx_buffer_tail;

From b7e9bb40749a1bd67a9130c3d8706e8f06a663e0 Mon Sep 17 00:00:00 2001
From: Matthijs Kooijman <matthijs@stdin.nl>
Date: Fri, 19 Apr 2013 12:56:54 +0200
Subject: [PATCH 09/15] Fix HardwareSerial::flush() when interrupts are kept
 disabled for a while

It turns out there is an additional corner case. The analysis in the
previous commit wrt to flush() assumes that the data register is always
kept filled by the interrupt handler, so the TXC bit won't get set until
all the queued bytes have been transmitted. But, when interrupts are
disabled for a longer period (for example when an interrupt handler for
another device is running for longer than 1-2 byte times), it could
happen that the UART stops transmitting while there are still more bytes
queued (but these are in the buffer, not in the UDR register, so the
UART can't know about them).

In this case, the TXC bit would get set, but the transmission is not
complete yet. We can easily detect this case by looking at the head and
tail pointers, but it seems easier to instead look at the UDRIE bit
(the TX interrupt is enabled if and only if there are bytes in the
queue). To fix this corner case, this commit:
 - Checks the UDRIE bit and only if it is unset, looks at the TXC bit.
 - Moves the clearing of TXC from write() to the tx interrupt handler.
   This (still) causes the TXC bit to be cleared whenever a byte is
   queued when the buffer is empty (in this case the tx interrupt will
   trigger directly after write() is called). It also causes the TXC bit
   to be cleared whenever transmission is resumed after it halted
   because interrupts have been disabled for too long.

As a side effect, another race condition is prevented. This could occur
at very high bitrates, where the transmission would be completed before
the code got time to clear the TXC0 register, making the clear happen
_after_ the transmission was already complete. With the new code, the
clearing of TXC happens directly after writing to the UDR register,
while interrupts are disabled, and we can be certain the data
transmission needs more time than one instruction to complete. This
fixes #1463 and replaces #1456.
---
 .../arduino/avr/cores/arduino/HardwareSerial.cpp  | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
index 6a97cf726ae..3fa124c6a93 100644
--- a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
@@ -233,6 +233,11 @@ void HardwareSerial::_tx_udr_empty_irq(void)
     _tx_buffer_tail = (_tx_buffer_tail + 1) % SERIAL_BUFFER_SIZE;
 
     *_udr = c;
+
+    // clear the TXC bit -- "can be cleared by writing a one to its bit
+    // location". This makes sure flush() won't return until the bytes
+    // actually got written
+    sbi(*_ucsra, TXC0);
   }
 }
 
@@ -344,9 +349,9 @@ void HardwareSerial::flush()
   if (!_written)
     return;
 
-  // UDR is kept full while the buffer is not empty, so TXC triggers
-  // when EMPTY && SENT
-  while (bit_is_clear(*_ucsra, TXC0));
+  while (bit_is_set(*_ucsrb, UDRIE0) || bit_is_clear(*_ucsra, TXC0));
+  // If we get here, nothing is queued anymore (DRIE is disabled) and
+  // the hardware finished tranmission (TXC is set).
 }
 
 size_t HardwareSerial::write(uint8_t c)
@@ -364,10 +369,6 @@ size_t HardwareSerial::write(uint8_t c)
 	
   sbi(*_ucsrb, UDRIE0);
   _written = true;
-  // clear the TXC bit -- "can be cleared by writing a one to its bit
-  // location". This makes sure flush() won't return until the bytes
-  // actually got written
-  sbi(*_ucsra, TXC0);
   
   return 1;
 }

From eb86af7b67407e198bac24ecd16a8c1669e3efaa Mon Sep 17 00:00:00 2001
From: Matthijs Kooijman <matthijs@stdin.nl>
Date: Thu, 18 Apr 2013 21:34:00 +0200
Subject: [PATCH 10/15] Fix lockup when writing to HardwareSerial with
 interrupts disabled

When interrupts are disabled, writing to HardwareSerial could cause a
lockup. When the tx buffer is full, a busy-wait loop is used to wait for
the interrupt handler to free up a byte in the buffer. However, when
interrupts are disabled, this will of course never happen and the
Arduino will lock up. This often caused lockups when doing (big) debug
printing from an interrupt handler.

Additionally, calling flush() with interrupts disabled while
transmission was in progress would also cause a lockup.

When interrupts are disabled, the code now actively checks the UDRE
(UART Data Register Empty) and calls the interrupt handler to free up
room if the bit is set.

This can lead to delays in interrupt handlers when the serial buffer is
full, but a delay is of course always preferred to a lockup.

Closes: #672
References: #1147
---
 .../avr/cores/arduino/HardwareSerial.cpp      | 26 +++++++++++++++----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
index 3fa124c6a93..59e5d143319 100644
--- a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
@@ -349,7 +349,14 @@ void HardwareSerial::flush()
   if (!_written)
     return;
 
-  while (bit_is_set(*_ucsrb, UDRIE0) || bit_is_clear(*_ucsra, TXC0));
+  while (bit_is_set(*_ucsrb, UDRIE0) || bit_is_clear(*_ucsra, TXC0)) {
+    if (bit_is_clear(SREG, SREG_I) && bit_is_set(*_ucsrb, UDRIE0))
+	// Interrupts are globally disabled, but the DR empty
+	// interrupt should be enabled, so poll the DR empty flag to
+	// prevent deadlock
+	if (bit_is_set(*_ucsra, UDRE0))
+	  _tx_udr_empty_irq();
+  }
   // If we get here, nothing is queued anymore (DRIE is disabled) and
   // the hardware finished tranmission (TXC is set).
 }
@@ -360,10 +367,19 @@ size_t HardwareSerial::write(uint8_t c)
 	
   // If the output buffer is full, there's nothing for it other than to 
   // wait for the interrupt handler to empty it a bit
-  // ???: return 0 here instead?
-  while (i == _tx_buffer_tail)
-    ;
-	
+  while (i == _tx_buffer_tail) {
+    if (bit_is_clear(SREG, SREG_I)) {
+      // Interrupts are disabled, so we'll have to poll the data
+      // register empty flag ourselves. If it is set, pretend an
+      // interrupt has happened and call the handler to free up
+      // space for us.
+      if(bit_is_set(*_ucsra, UDRE0))
+	_tx_udr_empty_irq();
+    } else {
+      // nop, the interrupt handler will free up space for us
+    }
+  }
+
   _tx_buffer[_tx_buffer_head] = c;
   _tx_buffer_head = i;
 	

From 7c337d23aada70aeb005081cbe4e965a5effa8bd Mon Sep 17 00:00:00 2001
From: Matthijs Kooijman <matthijs@stdin.nl>
Date: Thu, 18 Apr 2013 19:06:00 +0200
Subject: [PATCH 11/15] Disable the UDRE interrupt sooner in HardwareSerial

Before, the interrupt was disabled when it was triggered and it turned
out there was no data to send. However, the interrupt can be disabled
already when the last byte is written to the UART, since write() will
always re-enable the interrupt when it adds new data to the buffer.

Closes: #1008
---
 .../avr/cores/arduino/HardwareSerial.cpp      | 24 +++++++++----------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
index 59e5d143319..e361da663f2 100644
--- a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
@@ -223,22 +223,22 @@ void HardwareSerial::_rx_complete_irq(void)
 
 void HardwareSerial::_tx_udr_empty_irq(void)
 {
+  // If interrupts are enabled, there must be more data in the output
+  // buffer. Send the next byte
+  unsigned char c = _tx_buffer[_tx_buffer_tail];
+  _tx_buffer_tail = (_tx_buffer_tail + 1) % SERIAL_BUFFER_SIZE;
+
+  *_udr = c;
+
+  // clear the TXC bit -- "can be cleared by writing a one to its bit
+  // location". This makes sure flush() won't return until the bytes
+  // actually got written
+  sbi(*_ucsra, TXC0);
+
   if (_tx_buffer_head == _tx_buffer_tail) {
     // Buffer empty, so disable interrupts
     cbi(*_ucsrb, UDRIE0);
   }
-  else {
-    // There is more data in the output buffer. Send the next byte
-    unsigned char c = _tx_buffer[_tx_buffer_tail];
-    _tx_buffer_tail = (_tx_buffer_tail + 1) % SERIAL_BUFFER_SIZE;
-
-    *_udr = c;
-
-    // clear the TXC bit -- "can be cleared by writing a one to its bit
-    // location". This makes sure flush() won't return until the bytes
-    // actually got written
-    sbi(*_ucsra, TXC0);
-  }
 }
 
 // Constructors ////////////////////////////////////////////////////////////////

From a0d0bfbaaeeed9cb5c1f5fdc5202ef40349997a7 Mon Sep 17 00:00:00 2001
From: Matthijs Kooijman <matthijs@stdin.nl>
Date: Sun, 1 Dec 2013 17:21:54 +0100
Subject: [PATCH 12/15] Centrally decide which hardware UARTS are available

Before, this decision was made in few different places, based on
sometimes different register defines.

Now, HardwareSerial.h decides wich UARTS are available, defines
USE_HWSERIALn macros and HardwareSerial.cpp simply checks these macros
(together with some #ifs to decide which registers to use for UART 0).
For consistency, USBAPI.h also defines a HAVE_CDCSERIAL macro when
applicable.

For supported targets, this should change any behaviour. For unsupported
targets, the error messages might subtly change because some checks are
moved or changed.

Additionally, this moves the USBAPI.h include form HardareSerial.h into
Arduino.h and raises an error when both CDC serial and UART0 are
available (previously this would silently use UART0 instead of CDC, but
there is not currently any Atmel chip available for which this would
occur).
---
 hardware/arduino/avr/cores/arduino/Arduino.h  |  4 ++
 .../avr/cores/arduino/HardwareSerial.cpp      | 65 +++++++------------
 .../avr/cores/arduino/HardwareSerial.h        |  7 +-
 hardware/arduino/avr/cores/arduino/USBAPI.h   |  2 +
 4 files changed, 35 insertions(+), 43 deletions(-)

diff --git a/hardware/arduino/avr/cores/arduino/Arduino.h b/hardware/arduino/avr/cores/arduino/Arduino.h
index 3f125bc4c92..cf0555a564d 100644
--- a/hardware/arduino/avr/cores/arduino/Arduino.h
+++ b/hardware/arduino/avr/cores/arduino/Arduino.h
@@ -199,6 +199,10 @@ extern const uint8_t PROGMEM digital_pin_to_timer_PGM[];
 #include "WCharacter.h"
 #include "WString.h"
 #include "HardwareSerial.h"
+#include "USBAPI.h"
+#if defined(HAVE_HWSERIAL0) && defined(HAVE_CDCSERIAL)
+#error "Targets with both UART0 and CDC serial not supported"
+#endif
 
 uint16_t makeWord(uint16_t w);
 uint16_t makeWord(byte h, byte l);
diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
index e361da663f2..b4d2250891a 100644
--- a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
@@ -28,11 +28,11 @@
 #include "Arduino.h"
 #include "wiring_private.h"
 
+#include "HardwareSerial.h"
+
 // this next line disables the entire HardwareSerial.cpp, 
 // this is so I can support Attiny series and any other chip without a uart
-#if defined(UBRRH) || defined(UBRR0H) || defined(UBRR1H) || defined(UBRR2H) || defined(UBRR3H)
-
-#include "HardwareSerial.h"
+#if defined(HAVE_HWSERIAL0) || defined(HAVE_HWSERIAL1) || defined(HAVE_HWSERIAL2) || defined(HAVE_HWSERIAL3)
 
 // Ensure that the various bit positions we use are available with a 0
 // postfix, so we can always use the values for UART0 for all UARTs. The
@@ -84,53 +84,44 @@
 #error "Not all bit positions for UART3 are the same as for UART0"
 #endif
 
-#if !defined(USART0_RX_vect) && defined(USART1_RX_vect)
-// do nothing - on the 32u4 the first USART is USART1
-#else
-#if !defined(USART_RX_vect) && !defined(USART0_RX_vect) && \
-    !defined(USART_RXC_vect)
-  #error "Don't know what the Data Received vector is called for the first UART"
-#else
+#if defined(HAVE_HWSERIAL0)
   void serialEvent() __attribute__((weak));
   void serialEvent() {}
-  #define serialEvent_implemented
 #if defined(USART_RX_vect)
   ISR(USART_RX_vect)
 #elif defined(USART0_RX_vect)
   ISR(USART0_RX_vect)
 #elif defined(USART_RXC_vect)
   ISR(USART_RXC_vect) // ATmega8
+#else
+  #error "Don't know what the Data Received vector is called for the first UART"
 #endif
   {
     Serial._rx_complete_irq();
   }
 #endif
-#endif
 
-#if defined(USART1_RX_vect)
+#if defined(HAVE_HWSERIAL1)
   void serialEvent1() __attribute__((weak));
   void serialEvent1() {}
-  #define serialEvent1_implemented
   ISR(USART1_RX_vect)
   {
     Serial1._rx_complete_irq();
   }
 #endif
 
-#if defined(USART2_RX_vect) && defined(UDR2)
+#if defined(HAVE_HWSERIAL2)
   void serialEvent2() __attribute__((weak));
   void serialEvent2() {}
-  #define serialEvent2_implemented
   ISR(USART2_RX_vect)
   {
     Serial2._rx_complete_irq();
   }
 #endif
 
-#if defined(USART3_RX_vect) && defined(UDR3)
+#if defined(HAVE_HWSERIAL3)
   void serialEvent3() __attribute__((weak));
   void serialEvent3() {}
-  #define serialEvent3_implemented
   ISR(USART3_RX_vect)
   {
     Serial3._rx_complete_irq();
@@ -139,27 +130,22 @@
 
 void serialEventRun(void)
 {
-#ifdef serialEvent_implemented
+#if defined(HAVE_HWSERIAL0)
   if (Serial.available()) serialEvent();
 #endif
-#ifdef serialEvent1_implemented
+#if defined(HAVE_HWSERIAL1)
   if (Serial1.available()) serialEvent1();
 #endif
-#ifdef serialEvent2_implemented
+#if defined(HAVE_HWSERIAL2)
   if (Serial2.available()) serialEvent2();
 #endif
-#ifdef serialEvent3_implemented
+#if defined(HAVE_HWSERIAL3)
   if (Serial3.available()) serialEvent3();
 #endif
 }
 
 
-#if !defined(USART0_UDRE_vect) && defined(USART1_UDRE_vect)
-// do nothing - on the 32u4 the first USART is USART1
-#else
-#if !defined(UART0_UDRE_vect) && !defined(UART_UDRE_vect) && !defined(USART0_UDRE_vect) && !defined(USART_UDRE_vect)
-  #error "Don't know what the Data Register Empty vector is called for the first UART"
-#else
+#if defined(HAVE_HWSERIAL0)
 #if defined(UART0_UDRE_vect)
 ISR(UART0_UDRE_vect)
 #elif defined(UART_UDRE_vect)
@@ -168,28 +154,29 @@ ISR(UART_UDRE_vect)
 ISR(USART0_UDRE_vect)
 #elif defined(USART_UDRE_vect)
 ISR(USART_UDRE_vect)
+#else
+  #error "Don't know what the Data Register Empty vector is called for the first UART"
 #endif
 {
   Serial._tx_udr_empty_irq();
 }
 #endif
-#endif
 
-#ifdef USART1_UDRE_vect
+#if defined(HAVE_HWSERIAL1)
 ISR(USART1_UDRE_vect)
 {
   Serial1._tx_udr_empty_irq();
 }
 #endif
 
-#ifdef USART2_UDRE_vect
+#if defined(HAVE_HWSERIAL2)
 ISR(USART2_UDRE_vect)
 {
   Serial2._tx_udr_empty_irq();
 }
 #endif
 
-#ifdef USART3_UDRE_vect
+#if defined(HAVE_HWSERIAL3)
 ISR(USART3_UDRE_vect)
 {
   Serial3._tx_udr_empty_irq();
@@ -395,23 +382,21 @@ HardwareSerial::operator bool() {
 
 // Preinstantiate Objects //////////////////////////////////////////////////////
 
+#if defined(HAVE_HWSERIAL0)
 #if defined(UBRRH) && defined(UBRRL)
   HardwareSerial Serial(&UBRRH, &UBRRL, &UCSRA, &UCSRB, &UCSRC, &UDR);
-#elif defined(UBRR0H) && defined(UBRR0L)
-  HardwareSerial Serial(&UBRR0H, &UBRR0L, &UCSR0A, &UCSR0B, &UCSR0C, &UDR0);
-#elif defined(USBCON)
-  // do nothing - Serial object and buffers are initialized in CDC code
 #else
-  #error no serial port defined  (port 0)
+  HardwareSerial Serial(&UBRR0H, &UBRR0L, &UCSR0A, &UCSR0B, &UCSR0C, &UDR0);
+#endif
 #endif
 
-#if defined(UBRR1H)
+#if defined(HAVE_HWSERIAL1)
   HardwareSerial Serial1(&UBRR1H, &UBRR1L, &UCSR1A, &UCSR1B, &UCSR1C, &UDR1);
 #endif
-#if defined(UBRR2H)
+#if defined(HAVE_HWSERIAL2)
   HardwareSerial Serial2(&UBRR2H, &UBRR2L, &UCSR2A, &UCSR2B, &UCSR2C, &UDR2);
 #endif
-#if defined(UBRR3H)
+#if defined(HAVE_HWSERIAL3)
   HardwareSerial Serial3(&UBRR3H, &UBRR3L, &UCSR3A, &UCSR3B, &UCSR3C, &UDR3);
 #endif
 
diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial.h b/hardware/arduino/avr/cores/arduino/HardwareSerial.h
index c6649df83a6..8bf7744a2b7 100644
--- a/hardware/arduino/avr/cores/arduino/HardwareSerial.h
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial.h
@@ -113,18 +113,19 @@ class HardwareSerial : public Stream
 
 #if defined(UBRRH) || defined(UBRR0H)
   extern HardwareSerial Serial;
-#elif defined(USBCON)
-  #include "USBAPI.h"
-//  extern HardwareSerial Serial_;  
+  #define HAVE_HWSERIAL0
 #endif
 #if defined(UBRR1H)
   extern HardwareSerial Serial1;
+  #define HAVE_HWSERIAL1
 #endif
 #if defined(UBRR2H)
   extern HardwareSerial Serial2;
+  #define HAVE_HWSERIAL2
 #endif
 #if defined(UBRR3H)
   extern HardwareSerial Serial3;
+  #define HAVE_HWSERIAL3
 #endif
 
 extern void serialEventRun(void) __attribute__((weak));
diff --git a/hardware/arduino/avr/cores/arduino/USBAPI.h b/hardware/arduino/avr/cores/arduino/USBAPI.h
index da2e86961cc..5a330024cab 100644
--- a/hardware/arduino/avr/cores/arduino/USBAPI.h
+++ b/hardware/arduino/avr/cores/arduino/USBAPI.h
@@ -55,6 +55,8 @@ class Serial_ : public Stream
 };
 extern Serial_ Serial;
 
+#define HAVE_CDCSERIAL
+
 //================================================================================
 //================================================================================
 //	Mouse

From aa584bc518d3ea68c1ffa149ec5ed02ae10085f6 Mon Sep 17 00:00:00 2001
From: Matthijs Kooijman <matthijs@stdin.nl>
Date: Tue, 3 Dec 2013 21:15:17 +0100
Subject: [PATCH 13/15] Put each HardwareSerial instance in its own .cpp file

By putting the ISRs and HardwareSerial instance for each instance in a
separate compilation unit, the compile will only consider them for
linking when the instance is actually used. The ISR is always referenced
by the compiler runtime and the Serialx_available() function is always
referenced by SerialEventRun(), but both references are weak and thus do
not cause the compilation to be included in the link by themselves.

The effect of this is that when multiple HardwareSerial ports are
available, but not all are used, buffers are only allocated and ISRs are
only included for the serial ports that are used. On the mega, this
lowers memory usage from 653 bytes to just 182 when only using the first
serial port.

On boards with just a single port, there is no change, since the code
and memory was already left out when no serial port was used at all.

This fixes #1425 and fixes #1259.
---
 .../avr/cores/arduino/HardwareSerial.cpp      | 106 +++---------------
 .../avr/cores/arduino/HardwareSerial0.cpp     |  54 +++++++++
 .../avr/cores/arduino/HardwareSerial1.cpp     |  54 +++++++++
 .../avr/cores/arduino/HardwareSerial2.cpp     |  54 +++++++++
 .../avr/cores/arduino/HardwareSerial3.cpp     |  54 +++++++++
 5 files changed, 229 insertions(+), 93 deletions(-)
 create mode 100644 hardware/arduino/avr/cores/arduino/HardwareSerial0.cpp
 create mode 100644 hardware/arduino/avr/cores/arduino/HardwareSerial1.cpp
 create mode 100644 hardware/arduino/avr/cores/arduino/HardwareSerial2.cpp
 create mode 100644 hardware/arduino/avr/cores/arduino/HardwareSerial3.cpp

diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
index b4d2250891a..c62c3d46f9f 100644
--- a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
@@ -84,105 +84,46 @@
 #error "Not all bit positions for UART3 are the same as for UART0"
 #endif
 
+// SerialEvent functions are weak, so when the user doesn't define them,
+// the linker just sets their address to 0 (which is checked below).
+// The Serialx_available is just a wrapper around Serialx.available(),
+// but we can refer to it weakly so we don't pull in the entire
+// HardwareSerial instance if the user doesn't also refer to it.
 #if defined(HAVE_HWSERIAL0)
   void serialEvent() __attribute__((weak));
-  void serialEvent() {}
-#if defined(USART_RX_vect)
-  ISR(USART_RX_vect)
-#elif defined(USART0_RX_vect)
-  ISR(USART0_RX_vect)
-#elif defined(USART_RXC_vect)
-  ISR(USART_RXC_vect) // ATmega8
-#else
-  #error "Don't know what the Data Received vector is called for the first UART"
-#endif
-  {
-    Serial._rx_complete_irq();
-  }
+  bool Serial0_available() __attribute__((weak));
 #endif
 
 #if defined(HAVE_HWSERIAL1)
   void serialEvent1() __attribute__((weak));
-  void serialEvent1() {}
-  ISR(USART1_RX_vect)
-  {
-    Serial1._rx_complete_irq();
-  }
+  bool Serial1_available() __attribute__((weak));
 #endif
 
 #if defined(HAVE_HWSERIAL2)
   void serialEvent2() __attribute__((weak));
-  void serialEvent2() {}
-  ISR(USART2_RX_vect)
-  {
-    Serial2._rx_complete_irq();
-  }
+  bool Serial2_available() __attribute__((weak));
 #endif
 
 #if defined(HAVE_HWSERIAL3)
   void serialEvent3() __attribute__((weak));
-  void serialEvent3() {}
-  ISR(USART3_RX_vect)
-  {
-    Serial3._rx_complete_irq();
-  }
+  bool Serial3_available() __attribute__((weak));
 #endif
 
 void serialEventRun(void)
 {
 #if defined(HAVE_HWSERIAL0)
-  if (Serial.available()) serialEvent();
+  if (Serial0_available && serialEvent && Serial0_available()) serialEvent();
 #endif
 #if defined(HAVE_HWSERIAL1)
-  if (Serial1.available()) serialEvent1();
+  if (Serial1_available && serialEvent1 && Serial1_available()) serialEvent1();
 #endif
 #if defined(HAVE_HWSERIAL2)
-  if (Serial2.available()) serialEvent2();
+  if (Serial2_available && serialEvent2 && Serial2_available()) serialEvent2();
 #endif
 #if defined(HAVE_HWSERIAL3)
-  if (Serial3.available()) serialEvent3();
-#endif
-}
-
-
-#if defined(HAVE_HWSERIAL0)
-#if defined(UART0_UDRE_vect)
-ISR(UART0_UDRE_vect)
-#elif defined(UART_UDRE_vect)
-ISR(UART_UDRE_vect)
-#elif defined(USART0_UDRE_vect)
-ISR(USART0_UDRE_vect)
-#elif defined(USART_UDRE_vect)
-ISR(USART_UDRE_vect)
-#else
-  #error "Don't know what the Data Register Empty vector is called for the first UART"
-#endif
-{
-  Serial._tx_udr_empty_irq();
-}
-#endif
-
-#if defined(HAVE_HWSERIAL1)
-ISR(USART1_UDRE_vect)
-{
-  Serial1._tx_udr_empty_irq();
-}
+  if (Serial3_available && serialEvent2 && Serial3_available()) serialEvent3();
 #endif
-
-#if defined(HAVE_HWSERIAL2)
-ISR(USART2_UDRE_vect)
-{
-  Serial2._tx_udr_empty_irq();
-}
-#endif
-
-#if defined(HAVE_HWSERIAL3)
-ISR(USART3_UDRE_vect)
-{
-  Serial3._tx_udr_empty_irq();
 }
-#endif
-
 
 // Actual interrupt handlers //////////////////////////////////////////////////////////////
 
@@ -380,25 +321,4 @@ HardwareSerial::operator bool() {
 	return true;
 }
 
-// Preinstantiate Objects //////////////////////////////////////////////////////
-
-#if defined(HAVE_HWSERIAL0)
-#if defined(UBRRH) && defined(UBRRL)
-  HardwareSerial Serial(&UBRRH, &UBRRL, &UCSRA, &UCSRB, &UCSRC, &UDR);
-#else
-  HardwareSerial Serial(&UBRR0H, &UBRR0L, &UCSR0A, &UCSR0B, &UCSR0C, &UDR0);
-#endif
-#endif
-
-#if defined(HAVE_HWSERIAL1)
-  HardwareSerial Serial1(&UBRR1H, &UBRR1L, &UCSR1A, &UCSR1B, &UCSR1C, &UDR1);
-#endif
-#if defined(HAVE_HWSERIAL2)
-  HardwareSerial Serial2(&UBRR2H, &UBRR2L, &UCSR2A, &UCSR2B, &UCSR2C, &UDR2);
-#endif
-#if defined(HAVE_HWSERIAL3)
-  HardwareSerial Serial3(&UBRR3H, &UBRR3L, &UCSR3A, &UCSR3B, &UCSR3C, &UDR3);
-#endif
-
 #endif // whole file
-
diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial0.cpp b/hardware/arduino/avr/cores/arduino/HardwareSerial0.cpp
new file mode 100644
index 00000000000..dd4d806c756
--- /dev/null
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial0.cpp
@@ -0,0 +1,54 @@
+#include "Arduino.h"
+#include "HardwareSerial.h"
+
+// Each HardwareSerial is defined in its own file, sine the linker pulls
+// in the entire file when any element inside is used. --gc-sections can
+// additionally cause unused symbols to be dropped, but ISRs have the
+// "used" attribute so are never dropped and they keep the
+// HardwareSerial instance in as well. Putting each instance in its own
+// file prevents the linker from pulling in any unused instances in the
+// first place.
+
+#if defined(HAVE_HWSERIAL0)
+
+#if defined(USART_RX_vect)
+  ISR(USART_RX_vect)
+#elif defined(USART0_RX_vect)
+  ISR(USART0_RX_vect)
+#elif defined(USART_RXC_vect)
+  ISR(USART_RXC_vect) // ATmega8
+#else
+  #error "Don't know what the Data Received vector is called for the first UART"
+#endif
+  {
+    Serial._rx_complete_irq();
+  }
+
+#if defined(UART0_UDRE_vect)
+ISR(UART0_UDRE_vect)
+#elif defined(UART_UDRE_vect)
+ISR(UART_UDRE_vect)
+#elif defined(USART0_UDRE_vect)
+ISR(USART0_UDRE_vect)
+#elif defined(USART_UDRE_vect)
+ISR(USART_UDRE_vect)
+#else
+  #error "Don't know what the Data Register Empty vector is called for the first UART"
+#endif
+{
+  Serial._tx_udr_empty_irq();
+}
+
+#if defined(UBRRH) && defined(UBRRL)
+  HardwareSerial Serial(&UBRRH, &UBRRL, &UCSRA, &UCSRB, &UCSRC, &UDR);
+#else
+  HardwareSerial Serial(&UBRR0H, &UBRR0L, &UCSR0A, &UCSR0B, &UCSR0C, &UDR0);
+#endif
+
+// Function that can be weakly referenced by serialEventRun to prevent
+// pulling in this file if it's not otherwise used.
+bool Serial0_available() {
+  return Serial.available();
+}
+
+#endif // HAVE_HWSERIAL0
diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial1.cpp b/hardware/arduino/avr/cores/arduino/HardwareSerial1.cpp
new file mode 100644
index 00000000000..c04263e52c4
--- /dev/null
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial1.cpp
@@ -0,0 +1,54 @@
+#include "Arduino.h"
+#include "HardwareSerial.h"
+
+// Each HardwareSerial is defined in its own file, sine the linker pulls
+// in the entire file when any element inside is used. --gc-sections can
+// additionally cause unused symbols to be dropped, but ISRs have the
+// "used" attribute so are never dropped and they keep the
+// HardwareSerial instance in as well. Putting each instance in its own
+// file prevents the linker from pulling in any unused instances in the
+// first place.
+
+#if defined(HAVE_HWSERIAL1)
+
+#if defined(USART_RX_vect)
+  ISR(USART_RX_vect)
+#elif defined(USART1_RX_vect)
+  ISR(USART1_RX_vect)
+#elif defined(USART_RXC_vect)
+  ISR(USART_RXC_vect) // ATmega8
+#else
+  #error "Don't know what the Data Received vector is called for the first UART"
+#endif
+  {
+    Serial1._rx_complete_irq();
+  }
+
+#if defined(UART1_UDRE_vect)
+ISR(UART1_UDRE_vect)
+#elif defined(UART_UDRE_vect)
+ISR(UART_UDRE_vect)
+#elif defined(USART1_UDRE_vect)
+ISR(USART1_UDRE_vect)
+#elif defined(USART_UDRE_vect)
+ISR(USART_UDRE_vect)
+#else
+  #error "Don't know what the Data Register Empty vector is called for the first UART"
+#endif
+{
+  Serial1._tx_udr_empty_irq();
+}
+
+#if defined(UBRRH) && defined(UBRRL)
+  HardwareSerial Serial1(&UBRRH, &UBRRL, &UCSRA, &UCSRB, &UCSRC, &UDR);
+#else
+  HardwareSerial Serial1(&UBRR1H, &UBRR1L, &UCSR1A, &UCSR1B, &UCSR1C, &UDR1);
+#endif
+
+// Function that can be weakly referenced by serialEventRun to prevent
+// pulling in this file if it's not otherwise used.
+bool Serial1_available() {
+  return Serial1.available();
+}
+
+#endif // HAVE_HWSERIAL1
diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial2.cpp b/hardware/arduino/avr/cores/arduino/HardwareSerial2.cpp
new file mode 100644
index 00000000000..2c448f9372b
--- /dev/null
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial2.cpp
@@ -0,0 +1,54 @@
+#include "Arduino.h"
+#include "HardwareSerial.h"
+
+// Each HardwareSerial is defined in its own file, sine the linker pulls
+// in the entire file when any element inside is used. --gc-sections can
+// additionally cause unused symbols to be dropped, but ISRs have the
+// "used" attribute so are never dropped and they keep the
+// HardwareSerial instance in as well. Putting each instance in its own
+// file prevents the linker from pulling in any unused instances in the
+// first place.
+
+#if defined(HAVE_HWSERIAL2)
+
+#if defined(USART_RX_vect)
+  ISR(USART_RX_vect)
+#elif defined(USART2_RX_vect)
+  ISR(USART2_RX_vect)
+#elif defined(USART_RXC_vect)
+  ISR(USART_RXC_vect) // ATmega8
+#else
+  #error "Don't know what the Data Received vector is called for the first UART"
+#endif
+  {
+    Serial2._rx_complete_irq();
+  }
+
+#if defined(UART2_UDRE_vect)
+ISR(UART2_UDRE_vect)
+#elif defined(UART_UDRE_vect)
+ISR(UART_UDRE_vect)
+#elif defined(USART2_UDRE_vect)
+ISR(USART2_UDRE_vect)
+#elif defined(USART_UDRE_vect)
+ISR(USART_UDRE_vect)
+#else
+  #error "Don't know what the Data Register Empty vector is called for the first UART"
+#endif
+{
+  Serial2._tx_udr_empty_irq();
+}
+
+#if defined(UBRRH) && defined(UBRRL)
+  HardwareSerial Serial2(&UBRRH, &UBRRL, &UCSRA, &UCSRB, &UCSRC, &UDR);
+#else
+  HardwareSerial Serial2(&UBRR2H, &UBRR2L, &UCSR2A, &UCSR2B, &UCSR2C, &UDR2);
+#endif
+
+// Function that can be weakly referenced by serialEventRun to prevent
+// pulling in this file if it's not otherwise used.
+bool Serial2_available() {
+  return Serial2.available();
+}
+
+#endif // HAVE_HWSERIAL2
diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial3.cpp b/hardware/arduino/avr/cores/arduino/HardwareSerial3.cpp
new file mode 100644
index 00000000000..012839df8a6
--- /dev/null
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial3.cpp
@@ -0,0 +1,54 @@
+#include "Arduino.h"
+#include "HardwareSerial.h"
+
+// Each HardwareSerial is defined in its own file, sine the linker pulls
+// in the entire file when any element inside is used. --gc-sections can
+// additionally cause unused symbols to be dropped, but ISRs have the
+// "used" attribute so are never dropped and they keep the
+// HardwareSerial instance in as well. Putting each instance in its own
+// file prevents the linker from pulling in any unused instances in the
+// first place.
+
+#if defined(HAVE_HWSERIAL3)
+
+#if defined(USART_RX_vect)
+  ISR(USART_RX_vect)
+#elif defined(USART3_RX_vect)
+  ISR(USART3_RX_vect)
+#elif defined(USART_RXC_vect)
+  ISR(USART_RXC_vect) // ATmega8
+#else
+  #error "Don't know what the Data Received vector is called for the first UART"
+#endif
+  {
+    Serial3._rx_complete_irq();
+  }
+
+#if defined(UART3_UDRE_vect)
+ISR(UART3_UDRE_vect)
+#elif defined(UART_UDRE_vect)
+ISR(UART_UDRE_vect)
+#elif defined(USART3_UDRE_vect)
+ISR(USART3_UDRE_vect)
+#elif defined(USART_UDRE_vect)
+ISR(USART_UDRE_vect)
+#else
+  #error "Don't know what the Data Register Empty vector is called for the first UART"
+#endif
+{
+  Serial3._tx_udr_empty_irq();
+}
+
+#if defined(UBRRH) && defined(UBRRL)
+  HardwareSerial Serial3(&UBRRH, &UBRRL, &UCSRA, &UCSRB, &UCSRC, &UDR);
+#else
+  HardwareSerial Serial3(&UBRR3H, &UBRR3L, &UCSR3A, &UCSR3B, &UCSR3C, &UDR3);
+#endif
+
+// Function that can be weakly referenced by serialEventRun to prevent
+// pulling in this file if it's not otherwise used.
+bool Serial3_available() {
+  return Serial3.available();
+}
+
+#endif // HAVE_HWSERIAL3

From e1599f3c3995444345e9868a734ca015db91ae89 Mon Sep 17 00:00:00 2001
From: Matthijs Kooijman <matthijs@stdin.nl>
Date: Thu, 18 Apr 2013 16:55:06 +0200
Subject: [PATCH 14/15] Make all access to the HardwareSerial ringbuffers
 atomic

This prevents a potential race condition where for example write() would
detect that there is room in the tx buffer, an interrupt would trigger
where the interrupt handler writes to Serial filling up that room, and
write() would then reset the head pointer, effectively throwing away the
bytes written by the interrupt handler.

References: #1147
---
 .../avr/cores/arduino/HardwareSerial.cpp      | 90 ++++++++++++-------
 1 file changed, 56 insertions(+), 34 deletions(-)

diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
index c62c3d46f9f..45b5cbe2653 100644
--- a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
@@ -25,6 +25,8 @@
 #include <stdio.h>
 #include <string.h>
 #include <inttypes.h>
+#include <util/atomic.h>
+#include <avr/cpufunc.h>
 #include "Arduino.h"
 #include "wiring_private.h"
 
@@ -245,27 +247,33 @@ void HardwareSerial::end()
 
 int HardwareSerial::available(void)
 {
-  return (unsigned int)(SERIAL_BUFFER_SIZE + _rx_buffer_head - _rx_buffer_tail) % SERIAL_BUFFER_SIZE;
+  ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
+    return (unsigned int)(SERIAL_BUFFER_SIZE + _rx_buffer_head - _rx_buffer_tail) % SERIAL_BUFFER_SIZE;
+  }
 }
 
 int HardwareSerial::peek(void)
 {
-  if (_rx_buffer_head == _rx_buffer_tail) {
-    return -1;
-  } else {
-    return _rx_buffer[_rx_buffer_tail];
+  ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
+    if (_rx_buffer_head == _rx_buffer_tail) {
+      return -1;
+    } else {
+      return _rx_buffer[_rx_buffer_tail];
+    }
   }
 }
 
 int HardwareSerial::read(void)
 {
-  // if the head isn't ahead of the tail, we don't have any characters
-  if (_rx_buffer_head == _rx_buffer_tail) {
-    return -1;
-  } else {
-    unsigned char c = _rx_buffer[_rx_buffer_tail];
-    _rx_buffer_tail = (unsigned int)(_rx_buffer_tail + 1) % SERIAL_BUFFER_SIZE;
-    return c;
+  ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
+    // if the head isn't ahead of the tail, we don't have any characters
+    if (_rx_buffer_head == _rx_buffer_tail) {
+      return -1;
+    } else {
+      unsigned char c = _rx_buffer[_rx_buffer_tail];
+      _rx_buffer_tail = (unsigned int)(_rx_buffer_tail + 1) % SERIAL_BUFFER_SIZE;
+      return c;
+    }
   }
 }
 
@@ -291,30 +299,44 @@ void HardwareSerial::flush()
 
 size_t HardwareSerial::write(uint8_t c)
 {
-  int i = (_tx_buffer_head + 1) % SERIAL_BUFFER_SIZE;
-	
-  // If the output buffer is full, there's nothing for it other than to 
-  // wait for the interrupt handler to empty it a bit
-  while (i == _tx_buffer_tail) {
-    if (bit_is_clear(SREG, SREG_I)) {
-      // Interrupts are disabled, so we'll have to poll the data
-      // register empty flag ourselves. If it is set, pretend an
-      // interrupt has happened and call the handler to free up
-      // space for us.
-      if(bit_is_set(*_ucsra, UDRE0))
-	_tx_udr_empty_irq();
-    } else {
-      // nop, the interrupt handler will free up space for us
+  bool interrupts_enabled = bit_is_set(SREG, SREG_I);
+  ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
+    int i = (_tx_buffer_head + 1) % SERIAL_BUFFER_SIZE;
+
+    // If the output buffer is full, there's nothing for it other than to 
+    // wait for the interrupt handler to empty it a bit
+    while (i == _tx_buffer_tail) {
+      if (!interrupts_enabled) {
+	// Interrupts were disabled at the start of this function, so we
+	// can't just enable them (that would allow other interrupts to
+	// trigger as well!). We'll have to poll the data register empty
+	// flag ourselves. If it is set, pretend an interrupt has happened
+	// and call the handler to free up space for us.
+	if(bit_is_set(*_ucsra, UDRE0))
+	  _tx_udr_empty_irq();
+      } else {
+	// Interrupts were enabled, so we can temporarily enable them so
+	// our tx interrupt can fire and free up some space. Note that we
+	// can't just use the UDRE polling approach here instead of
+	// enabling interrupts, since that would prevent other
+	// interrupts from triggering while we wait for room.
+	NONATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
+	  _NOP(); // Any pending interrupts will trigger here
+	}
+	// Recalculate i, since other interrupt handlers might have
+	// written to our buffer
+	i = (_tx_buffer_head + 1) % SERIAL_BUFFER_SIZE;
+      }
     }
-  }
 
-  _tx_buffer[_tx_buffer_head] = c;
-  _tx_buffer_head = i;
-	
-  sbi(*_ucsrb, UDRIE0);
-  _written = true;
-  
-  return 1;
+    _tx_buffer[_tx_buffer_head] = c;
+    _tx_buffer_head = i;
+
+    sbi(*_ucsrb, UDRIE0);
+    _written = true;
+
+    return 1;
+  }
 }
 
 HardwareSerial::operator bool() {

From 6e0335218ca6dd401e04293aacaa13018d64042c Mon Sep 17 00:00:00 2001
From: Matthijs Kooijman <matthijs@stdin.nl>
Date: Wed, 18 Dec 2013 23:21:45 +0100
Subject: [PATCH 15/15] In HardwareSerial::write, bypass the queue when it's
 empty

This helps improve the effective datarate on high (>500kbit/s) bitrates,
by skipping the interrupt and associated overhead. At 1 Mbit/s the
implementation previously got up to about 600-700 kbit/s, but now it
actually gets up to the 1Mbit/s (values are rough estimates, though).
---
 hardware/arduino/avr/cores/arduino/HardwareSerial.cpp | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
index 45b5cbe2653..c611492a1db 100644
--- a/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
+++ b/hardware/arduino/avr/cores/arduino/HardwareSerial.cpp
@@ -301,6 +301,15 @@ size_t HardwareSerial::write(uint8_t c)
 {
   bool interrupts_enabled = bit_is_set(SREG, SREG_I);
   ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
+    // If the buffer and the data register is empty, just write the byte
+    // to the data register and be done. This shortcut helps
+    // significantly improve the effective datarate at high (>
+    // 500kbit/s) bitrates, where interrupt overhead becomes a slowdown.
+    if (_tx_buffer_head == _tx_buffer_tail && bit_is_set(*_ucsra, UDRE0)) {
+      *_udr = c;
+      sbi(*_ucsra, TXC0);
+      return 1;
+    }
     int i = (_tx_buffer_head + 1) % SERIAL_BUFFER_SIZE;
 
     // If the output buffer is full, there's nothing for it other than to