How to Increase the Arduino I2C Buffer Size?

greengobw · May 15, 2023, 4:27am

Hi
I have read some information and know to use build_flags, here is my platformio.ini

BUFFER_LENGTH was in
c:\Users\001.platformio\packages\framework-arduino-avr\libraries\Wire\src\Wire.h

SERIAL_RX_BUFFER_SIZE was in
c:\Users\001.platformio\packages\framework-arduino-avr\cores\arduino\HardwareSerial.h

But only the buffer size of the serial port is changed, and the I2C buffer size is not changed.
Am I missing any steps?

maxgerhardt · May 15, 2023, 8:17am

It’s a hardcoded define with no room for changes.

github.com

arduino/ArduinoCore-avr/blob/eabd762a1edcf076877b7bec28b7f99099141473/libraries/Wire/src/Wire.h#L29-L39


      
          #define BUFFER_LENGTH 32
          
          
// WIRE_HAS_END means Wire has end()
          #define WIRE_HAS_END 1
          
          
class TwoWire : public Stream
          {
            private:
              static uint8_t rxBuffer[];
              static uint8_t rxBufferIndex;
              static uint8_t rxBufferLength;

Also since the variables at line 38 and 39 are of type uint8_t, the maximum buffer length is 255… or maybe 254 if there’s some problems with overflow and “+1” checks.

You’d have to do a patch to the Arduino framework to get what you want.

But have you already verified your applicaiton still works with the buffer length changed directly in the source file?

greengobw · May 15, 2023, 12:38pm

thank you i understand.
I may consider reducing my data to 32byte or use the method of split transmission.

petedd · August 28, 2024, 10:09pm

I suffered from this affliction as well, but on the ESP32. Here is a clean solution which is not subject to being overwritten by an update of the Wire.h library. In platformio.ini:

build_flags = 
    -DI2C_BUFFER_LENGTH=255