Different Libraries (Wire.h) for Pro Mini and MKR Zero?

littek · December 21, 2017, 8:36am

Hello,
as far as I know the Wire library is the same for all the boards no matter if I have a Pro Mini or a MKRZero, correct?

I have an existing project for Pro Mini, but since the performance is not sufficient I want to change to the MKR Zero. I am using the online Editor of Arduino and include the "Wire.h" standard library. Furthermore I use another library for a DMP (digital motion processor) which is connected via the I2C, so the library of the DMP is using the macros from Wire.h

When I choose the Board "Pro Mini" all sketches compile correctly. When I choose the MKR Zero it terminates with an error:
'BUFFER_LENGTH' was not declared in this scope

Since BUFFER_LENGTH is a macro defined in the Wire.h (see link below) I am asking if there are different libraries called "Wire" for each different processor on Arduino boards. If not: What exactly changes when I choose "MKR Zero" instead of "Pro Mini" in the Webeditor?

Thanks beforehand!

Link: Arduino/Wire.h at master · esp8266/Arduino · GitHub
BUFFER_LENGTH is defined in line 32

pert · December 21, 2017, 10:31am

littek:
as far as I know the Wire library is the same for all the boards no matter if I have a Pro Mini or a MKRZero, correct?

Incorrect. The Wire library is hardware specific so each hardware package bundles its own version of it. The Wire library associated with the hardware package of the currently selected board is used. So when you select Tools > Board > Arduino Pro or Pro Mini This library is used:

Which does contain the BUFFER_LENGTH definition here:

github.com

arduino/ArduinoCore-avr/blob/3f63f2975e7183c3254b6794bfcc8f19ca0301c9/libraries/Wire/src/Wire.h#L28


      
          
            Modified 2012 by Todd Krein (todd@krein.org) to implement repeated starts
          */
          
          #ifndef TwoWire_h
          #define TwoWire_h
          
          #include <inttypes.h>
          #include "Stream.h"
          
          #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;

When you select Tools > Board > Arduino MKRZERO this Wire library is used:

which does not contain any buffer length definition. It does include RingBuffer.h:

github.com

arduino/ArduinoCore-samd/blob/master/libraries/Wire/Wire.h#L27


      
          * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
          */
          
          #ifndef TwoWire_h
          #define TwoWire_h
          
          #include "api/HardwareI2C.h"
          #include "variant.h"
          #include "SERCOM.h"
          
          // WIRE_HAS_END means Wire has end()
          #define WIRE_HAS_END 1
          
          namespace arduino {
          
          class TwoWire : public HardwareI2C
          {
           public:
             TwoWire(SERCOM *s, uint8_t pinSDA, uint8_t pinSCL);
             void begin();
             void begin(uint8_t address, bool enableGeneralCall);

Which contains the following definition:

github.com

arduino/ArduinoCore-samd/blob/master/cores/arduino/RingBuffer.h#L28


      
          
          #ifdef __cplusplus
          
          #ifndef _RING_BUFFER_
          #define _RING_BUFFER_
          
          #include <stdint.h>
          
          // 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.
          #ifndef SERIAL_BUFFER_SIZE
          #define SERIAL_BUFFER_SIZE 256
          #endif
          
          template <int N>
          class RingBufferN
          {
            public:
              uint8_t _aucBuffer[N] ;

#define SERIAL_BUFFER_SIZE 64

Without looking closer at the code I can't be sure if that will be the SAMD equivalent of BUFFER_LENGTH.

littek:
Link: Arduino/libraries/Wire/Wire.h at master · esp8266/Arduino · GitHub
BUFFER_LENGTH is defined in line 32

That's the ESP8266 core for Arduino hardware package. It has nothing to do with the Pro Mini (which uses the Arduino AVR Boards hardware package). or the MKRZERO (which uses the Arduino SAMD Boards hardware package).

littek · December 21, 2017, 12:19pm

Thank you very much for your help, my bad...

Well, guess I will have to take a look if I can find MPU6050 libraries suiting the MKRZero, because sadly adding the missing BUFFER_LENGTH does not solve all problems.

But thanks for your detailed advise!

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