Move buffers into HardwareSerial

This removes the need for doing an extra pointer dereference on every
access to the buffers, shrinking the code by around 100 bytes.

The members for these buffers must be public for now, since the
interrupt handlers also need to access them. These can later be made
private again.

Furthermore, the struct ring_buffer was removed. This allows the all
head and tail pointers to be put into the HardwareSerial struct before
the actual buffers, so the pointers all end up in the first 32 bytes of
the struct that can be accessed using a single instruction (ldd).

References: #947

1 files changed, 22 insertions, 4 deletions

diff --git a/cores/arduino/HardwareSerial.h b/cores/arduino/HardwareSerial.h
index a73117f..a091e03 100644
--- a/cores/arduino/HardwareSerial.h
+++ b/cores/arduino/HardwareSerial.h
@@ -27,13 +27,19 @@
 
 #include "Stream.h"
 
-struct ring_buffer;
+// Define constants and variables for buffering incoming serial data.  We're
+// using a ring buffer (I think), in which head is the index of the location
+// to which to write the next incoming character and tail is the index of the
+// location from which to read.
+#if (RAMEND < 1000)
+  #define SERIAL_BUFFER_SIZE 16
+#else
+  #define SERIAL_BUFFER_SIZE 64
+#endif
 
 class HardwareSerial : public Stream
 {
   private:
-    ring_buffer *_rx_buffer;
-    ring_buffer *_tx_buffer;
     volatile uint8_t *_ubrrh;
     volatile uint8_t *_ubrrl;
     volatile uint8_t *_ucsra;
@@ -46,8 +52,20 @@ class HardwareSerial : public Stream
     uint8_t _udrie;
     uint8_t _u2x;
     bool transmitting;
+
   public:
-    HardwareSerial(ring_buffer *rx_buffer, ring_buffer *tx_buffer,
+    volatile uint8_t _rx_buffer_head;
+    volatile uint8_t _rx_buffer_tail;
+    volatile uint8_t _tx_buffer_head;
+    volatile uint8_t _tx_buffer_tail;
+
+    // Don't put any members after these buffers, since only the first
+    // 32 bytes of this struct can be accessed quickly using the ldd
+    // instruction.
+    unsigned char _rx_buffer[SERIAL_BUFFER_SIZE];
+    unsigned char _tx_buffer[SERIAL_BUFFER_SIZE];
+
+    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,