[Due] (I2C) Wire.endTransmission always returns non-zero.

[chriskner]

1.5.1r2

It looks like endTransmission returns the number of bytes sent from the transmit buffer, not an indication of success, as http://arduino.cc/en/Reference/WireEndTransmission suggests.

from \arduino-1.5.1r2\hardware\arduino\sam\system\libsam\source\twi.c :

uint8_t TwoWire::endTransmission(uint8_t sendStop) {
    ...
    while (sent < txBufferLength) {
        ...
    }
    ...
    return sent;
}

[nathanhere]

I also just tested the return value of endTransmission, and it definitely has a bug. I tried sending 5 bytes over I2C, and it returned the number 5. This is only supposed to return a value of 0 - 4.

[lestofante]

The bug is in the lib or in the reference?
Il giorno 31/gen/2013 23:11, "Nathan" notifications@github.com ha scritto:

I also just tested the return value of endTransmission, and it definitely
has a bug. I tried sending 5 bytes over I2C, and it returned the number 5.
This is only supposed to return a value of 0 - 4.

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/1251#issuecomment-12968881.

[chriskner]

Unfortunately, the more you dig, the worse it gets.

It appears to me the devs at one point realized the work ahead of them was not trivial, and decided to supply a base-line functionality (below current standards). This is not a meant as a dig, just reality.

Any proc in the Wire library that accesses the I2C status register has been, or needs to be neutered (which is why I believe endTransmission got mangled in this version). Basically, any marginally serious I2C communication must bypass this version of the library, and twiddle the MCU registers directly.

Just scan the datasheet and look for bits that are "clear[ed] on read". This is totally not handled properly in 1.5.1r2.

[leszekru]

does not work in 1.5.2...
Is there a software i2c lib that works on Due???

[zelfkoelman]

Any news on this topic? I'm totally stuck in getting a PCA9622 Led driver to work over i2c... The Arduino gets stuck in the endTransmission function.

[sandeepmistry]

The return code has been addressed by @bluesign2k's commit e079baa and is already in master.