Wire buffer length improvments. (#8398)

* Enable I2C_BUFFER_LENGTH definition for Wire lib

Based on
paclema/arduino-esp32@375a89e

We should have been very careful when #defining things to not use a name
that could conflict with the user's own code, so this marks that old
define as deprecated.

If you opt-into the new behavior, you do not get the old BUFFER_LENGTH
constant.

As a bonus, changing these uint8_ts to size_t both reduces the code
size & improves performance.

* Increase buffer indexing variable size

I looked over the users of these variables and they should be fine with
no additional changes. The existing methods already have an option to
use size_t rather than uint8_t.

There's a few methods which return int instead of size_t, which isn't
great from a portability perspective but will be fine since this only is
designed to run on the ESP8266.

libraries/Wire/Wire.cpp

@@ -40,14 +40,14 @@ extern "C" {
 
 // Initialize Class Variables //////////////////////////////////////////////////
 
-uint8_t TwoWire::rxBuffer[BUFFER_LENGTH];
-uint8_t TwoWire::rxBufferIndex = 0;
-uint8_t TwoWire::rxBufferLength = 0;
+uint8_t TwoWire::rxBuffer[I2C_BUFFER_LENGTH];
+size_t TwoWire::rxBufferIndex = 0;
+size_t TwoWire::rxBufferLength = 0;
 
 uint8_t TwoWire::txAddress = 0;
-uint8_t TwoWire::txBuffer[BUFFER_LENGTH];
-uint8_t TwoWire::txBufferIndex = 0;
-uint8_t TwoWire::txBufferLength = 0;
+uint8_t TwoWire::txBuffer[I2C_BUFFER_LENGTH];
+size_t TwoWire::txBufferIndex = 0;
+size_t TwoWire::txBufferLength = 0;
 
 uint8_t TwoWire::transmitting = 0;
 void (*TwoWire::user_onRequest)(void);
@@ -122,9 +122,9 @@ void TwoWire::setClockStretchLimit(uint32_t limit)
 
 size_t TwoWire::requestFrom(uint8_t address, size_t size, bool sendStop)
 {
-    if (size > BUFFER_LENGTH)
+    if (size > I2C_BUFFER_LENGTH)
     {
-        size = BUFFER_LENGTH;
+        size = I2C_BUFFER_LENGTH;
     }
     size_t read = (twi_readFrom(address, rxBuffer, size, sendStop) == 0) ? size : 0;
     rxBufferIndex = 0;
@@ -183,7 +183,7 @@ size_t TwoWire::write(uint8_t data)
 {
     if (transmitting)
     {
-        if (txBufferLength >= BUFFER_LENGTH)
+        if (txBufferLength >= I2C_BUFFER_LENGTH)
         {
             setWriteError();
             return 0;

libraries/Wire/Wire.h

@@ -28,24 +28,23 @@
 #include "Stream.h"
 
 
-
 #ifndef I2C_BUFFER_LENGTH
+// DEPRECATED: Do not use BUFFER_LENGTH, prefer I2C_BUFFER_LENGTH
 #define BUFFER_LENGTH 128
-#else
-#define BUFFER_LENGTH I2C_BUFFER_LENGTH
+#define I2C_BUFFER_LENGTH BUFFER_LENGTH
 #endif
 
 class TwoWire : public Stream
 {
 private:
     static uint8_t rxBuffer[];
-    static uint8_t rxBufferIndex;
-    static uint8_t rxBufferLength;
+    static size_t rxBufferIndex;
+    static size_t rxBufferLength;
 
     static uint8_t txAddress;
     static uint8_t txBuffer[];
-    static uint8_t txBufferIndex;
-    static uint8_t txBufferLength;
+    static size_t txBufferIndex;
+    static size_t txBufferLength;
 
     static uint8_t transmitting;
     static void (*user_onRequest)(void);