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.

1 files changed, 54 insertions, 0 deletions

diff --git a/cores/arduino/HardwareSerial0.cpp b/cores/arduino/HardwareSerial0.cpp
new file mode 100644
index 0000000..dd4d806
--- /dev/null
+++ b/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