Added 'TwoWire::setBufferSize()' to Wire library (#2962)

'setBufferSize()' allows to modify the receive buffer size (inspired by the ESP32 code)

Author: Lorandil

libraries/Wire/src/Wire.cpp

@@ -19,6 +19,8 @@
     You should have received a copy of the GNU Lesser General Public
     License along with this library; if not, write to the Free Software
     Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+
+    Modified May 2025 by Sven Bruns (Lorandil on GitHub) to support user defined buffer size (inspired by ESP32 code)
 */
 
 #include <Arduino.h>
@@ -46,6 +48,10 @@ TwoWire::TwoWire(i2c_inst_t *i2c, pin_size_t sda, pin_size_t scl) {
     _running = false;
     _txBegun = false;
     _buffLen = 0;
+
+    // allocate buffer memory early, so we don't fragment the heap later
+    _buffSize = WIRE_BUFFER_SIZE;
+    _buff = (uint8_t *)malloc(_buffSize);
 }
 
 bool TwoWire::setSDA(pin_size_t pin) {
@@ -158,6 +164,16 @@ void TwoWire::begin(uint8_t addr) {
         // ERROR
         return;
     }
+
+    // allocate buffer if necessary
+    if (!_buff) {
+        _buff = (uint8_t *)malloc(_buffSize);
+        if (!_buff) {
+            // ERROR
+            return;
+        }
+    }
+
     _slave = true;
     i2c_init(_i2c, _clkHz);
     i2c_set_slave_mode(_i2c, true, addr);
@@ -192,7 +208,7 @@ void TwoWire::onIRQ() {
     // First, pull off any data available
     if (irqstat & (1 << 2)) {
         // RX_FULL
-        if (_buffLen < (int)sizeof(_buff)) {
+        if (_buffLen < int(_buffSize)) {
             _buff[_buffLen++] = _i2c->hw->data_cmd & 0xff;
         } else {
             _i2c->hw->data_cmd;
@@ -271,7 +287,7 @@ void TwoWire::beginTransmission(uint8_t addr) {
 }
 
 size_t TwoWire::requestFrom(uint8_t address, size_t quantity, bool stopBit) {
-    if (!_running || _txBegun || !quantity || (quantity > sizeof(_buff))) {
+    if (!_running || _txBegun || !quantity || (quantity > _buffSize)) {
         return 0;
     }
 
@@ -448,7 +464,7 @@ size_t TwoWire::write(uint8_t ucData) {
             return 0;
         }
     } else {
-        if (!_txBegun || (_buffLen == sizeof(_buff))) {
+        if (!_txBegun || (_buffLen == int(_buffSize))) {
             return 0;
         }
         _buff[_buffLen++] = ucData;
@@ -745,6 +761,20 @@ void TwoWire::clearTimeoutFlag() {
     _timeoutFlag = false;
 }
 
+size_t TwoWire::setBufferSize(size_t bSize) {
+    if (_running) {
+        // ERROR - transmission already running. Report back current buffer size
+        return _buffSize;
+    }
+    // only free the buffer, if it already exists and the new size differs from the current one
+    if (_buff && (bSize != _buffSize)) {
+        free(_buff);
+        _buff = nullptr;
+    }
+    _buffSize = max(WIRE_BUFFER_SIZE_MIN, int(bSize)); // enforce minimum buffer size
+    return _buffSize;
+}
+
 #ifndef __WIRE0_DEVICE
 #define __WIRE0_DEVICE i2c0
 #endif

libraries/Wire/src/Wire.h

@@ -19,6 +19,8 @@
     You should have received a copy of the GNU Lesser General Public
     License along with this library; if not, write to the Free Software
     Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+
+    Modified May 2025 by Sven Bruns (Lorandil on GitHub) to support user defined buffer size (inspired by ESP32 code)
 */
 
 #pragma once
@@ -30,8 +32,14 @@
 // WIRE_HAS_END means Wire has end()
 #define WIRE_HAS_END 1
 
+// WIRE_HAS_BUFFER_SIZE means Wire has setBufferSize()
+#define WIRE_HAS_BUFFER_SIZE 1
+
 #ifndef WIRE_BUFFER_SIZE
-#define WIRE_BUFFER_SIZE 256
+#define WIRE_BUFFER_SIZE 256    // default size, if none is set using Wire::setBuffersize(size_t)
+#endif
+#ifndef WIRE_BUFFER_SIZE_MIN
+#define WIRE_BUFFER_SIZE_MIN 32 // minimum size for safe operation
 #endif
 
 class TwoWire : public HardwareI2C {
@@ -97,6 +105,8 @@ class TwoWire : public HardwareI2C {
     bool getTimeoutFlag(void);
     void clearTimeoutFlag(void);
 
+    size_t setBufferSize(size_t bSize);	// set buffer size (call prior to 'begin()')
+
     // IRQ callback
     void onIRQ();
 
@@ -115,7 +125,9 @@ class TwoWire : public HardwareI2C {
     bool _reset_with_timeout;
     void _handleTimeout(bool reset);
 
-    uint8_t _buff[WIRE_BUFFER_SIZE];
+    uint8_t *_buff;         // pointer to i2c buffer
+    size_t  _buffSize;      // current buffer size
+
     int _buffLen;
     int _buffOff;