No support for I2C restart condition at DUE; parameter sendStop in endTransmission not considered

[AmLimit]

With a DUE I try to connect a MMA8452 but get wrong answers. On scope I can see that the parameter "sendStop" in "uint8_t TwoWire::endTransmission(uint8_t sendStop)" has no effect - instead of a restart condition a stop condition followed by a new start condition is perfomed.
A look into source code offers that the parameter "sendStop" is not used. The header comments are ready but the code doesn't reflect the description.
As I understand the MMA845x manual a restart condition is necessary to handle queries, so the MMA8452 is currently not controllable by the wire library.
May be there are additional issues in twi.c to handle that issue.

[sngl]

The sendStop variable is a global variable and its value is used inside the ISR that manages the communication.

https://github.com/arduino/Arduino/blob/ide-1.5.x/hardware/arduino/avr/libraries/Wire/utility/twi.c#L383

[AmLimit]

I think the static variable "twi_sendStop"
https://github.com/arduino/Arduino/blob/ide-1.5.x/hardware/arduino/avr/libraries/Wire/utility/twi.c#L43

and the mentioned function parameter "sendStop"
https://github.com/arduino/Arduino/blob/ide-1.5.x/hardware/arduino/avr/libraries/Wire/Wire.cpp#L142

is not the same.

[mal333]

Can say same about requestFrom. As a parameter uint8_t sendStop exist, but not using in function.

[AmLimit]

If the item will not be fixed in nearer future: is there any work around to support a MMA845x accelerometer on a DUE?

[AmLimit]

Some good news: I found a way to use my MMA8452 on a DUE :-)

To perform the needed repeated start condition to handle the MMA8452 you have to use the internal address functionality of the SAM controller (Chapter TWI / Master Mode / Internal Address). Due to the MMA8452 uses 7-bit addressing this feature offers up to 3 automatically sent request bytes - you don't have to handle it manually (quite a good feature). If I didn't miss any information within the documentation the MMA8452 is always controlled by 1 byte register requests.
To use this feature with my DUE I added another overloaded method of TwoWire::requestFrom to support the needed parameter iaddress (and optionally isize) to TWI_StartRead:

\arduino-1.5.8\hardware\arduino\sam\libraries\Wire\Wire.cpp

uint8_t TwoWire::requestFrom(uint8_t address, uint8_t quantity, uint32_t iaddress, uint8_t isize) {
  if (quantity > BUFFER_LENGTH)
  quantity = BUFFER_LENGTH;

  // perform blocking read into buffer
  int readed = 0;
  TWI_StartRead(twi, address, iaddress, isize);
  do {
    // Stop condition must be set during the reception of last byte
    if (readed + 1 == quantity)
    TWI_SendSTOPCondition( twi);

    TWI_WaitByteReceived(twi, RECV_TIMEOUT);
    rxBuffer[readed++] = TWI_ReadByte(twi);
  } while (readed < quantity);
  TWI_WaitTransferComplete(twi, RECV_TIMEOUT);

  // set rx buffer iterator vars
  rxBufferIndex = 0;
  rxBufferLength = readed;

  return readed;
}

\arduino-1.5.8\hardware\arduino\sam\libraries\Wire\Wire.h

public:
  uint8_t requestFrom(uint8_t, uint8_t, uint32_t, uint8_t);

To use this new method call the used MMA8452Q.cpp needs some changes in registerRead and registersRead. To keep the opportunity to apply e.g. a NANO I added compiler directives to choose the right code depending on applied board. You can see that performing a request on a DUE is much more simple:

\MMA8452Q.cpp

static inline uint8_t registerRead(uint8_t addr) {
#ifdef _VARIANT_ARDUINO_DUE_X_
    Wire.requestFrom((uint8_t) MMA8452Q_ADDRESS, (uint8_t) 1, (uint32_t) addr, (uint8_t) 1);
#else
    Wire.beginTransmission(MMA8452Q_ADDRESS);
    Wire.write(addr);
    Wire.endTransmission(false);

    Wire.requestFrom(MMA8452Q_ADDRESS, 1);
#endif

    while (!Wire.available());
    return Wire.read();
}

static inline void registersRead(uint8_t addr, uint8_t data[], size_t count) {
#ifdef _VARIANT_ARDUINO_DUE_X_
    Wire.requestFrom((uint8_t) MMA8452Q_ADDRESS, (uint8_t) count, (uint32_t) addr, (uint8_t) 1);
#else
    Wire.beginTransmission(MMA8452Q_ADDRESS);
    Wire.write(addr);
    Wire.endTransmission(false);

    Wire.requestFrom(MMA8452Q_ADDRESS, count);
#endif

    while (Wire.available() < count);

    for (size_t i = 0; i < count; i++)
        data[i] = Wire.read();
}

I checked this out at DUE and NANO and both works fine.

I hope this will be helpful for some other users being held up by this problem. This is the first time for me to give support to others and it makes me happy done this small milestone to be having achieved in my life :-)

May be it's not the most structured solution, but for me it's currently ok. I would appreciate if one specialist on the arduino software would give me feedback to this. Some questions from me to this are:

• Is there a better solution for MMA8452Q.cpp to fit different boards automatically?
• Is this the right way to present solution suggestions or should it be done by creating new branches or doing other actions?

Your feedback is welcome.

[Reslof]

I'm working with the same hardware but I cannot seem to get the MMA8452 working. The read for the WHO_AM_I register is always 0. I am also working with the Wire1 interface as opposed to Wire but I've made the necessary adjustments and still nothing. Could you please post the files you modified above so I can see where I went wrong?

[AmLimit]

In my last post all additions to the existing files are listed.
But maybe I changed the MMA address - in my application it is set to
#define MMA8452Q_ADDRESS 0x1D
Do you control the SA0 pin? In my case it has to be set to HIGH to 'select' the MMA. If SA0 is LOW the MMA would not answer.
Changing the address to 0x1C inverts the behaviour.
Please post a feedback if the hint solves your problem.
I would have posted the files within this comment, but pasting source files is not supported. I think I would have to check it into the repository but don't know how to do this correctly right now.

[mal333]

AmLimit, thank a lot, it's work! Tested on MLX90614 &DUE, everything fine.

[Reslof]

After making the necessary adjustments and fixing the data types for my setup, I can confirm that the fix AmLimit provided for the Wire library works. I tested it with my Due and MMA8452Q breakout with the Wire1 bus. I deleted the non Due directives though.
Thanks!

[davidrojas]

This is issue is still open in Arduino 1.6.3
But your fix works like a charm, AmLimit, thank you so much, I've been banging my head against this for almost a week (different accelerometer, but same problem with the Wire library).
Just one thing, in the Arduno 1.6.x now the libraries for the due are in C:\Users\YourUser\AppData\Roaming\Arduino15\packages\arduino\hardware\sam\1.6.3\libraries\

[SeanTaba]

Good job AmLimit, thank you very much.