I2C libraries for ATTiny85?

Question

I want to transmit I2C data, using a Digispark ATTiny85 board:

• http://digistump.com/products/1
• http://digistump.com/wiki/digispark/tutorials/connecting

I've found the following I2C libraries. Which one is more lightweight, stable, bug-free, efficient, powerful, and easy to use?

• Adafruit's TinyWireM has not been updated in 2 years.

• felias-fogg's SoftI2CMaster has been updated within days of this post.

• lucullusTheOnly's TinyWire represents some years of improvements, "based on the TinyWireM and TinyWireS libraries". This version is recommended by BroHogan, co-creator of TinyWireM: https://playground.arduino.cc/Code/USIi2c

Wire seems under-featured:

"the default Arduino Wire() library does not support changes in bus speed or feature proper clock stretching support. This makes the default library only marginally functional" https://www.maxbotix.com/articles/095.htm

What other I2C libs are available for ATTiny? In the IDE i see Digispark SoftSerial, OneWire, and VirtualWire.

How do they all compare?

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Note, these other answers do not seem relevant to my question:

• What's the difference between all the Software Serial Libraries? Which one is Arduino Nano compatible?

• Alternatives to Wire library for I2C

Answer 1

I want to transmit I2C data...

A little vague.

Transmit to what device? How fast is your data rate (100kHz, 400kHz)? Your only transmitting and not reading anything back? What is the idling voltage of your I2C bus (to then ask if you have chosen correct pull-up resistor values for your intended bus speed)?

You mention that the Wire library doesn't support core clock speed changes without some hacking, but don't talk about the speed you intend to run the microcontroller or how fast you intend to use the I2C. I can guess 400kHz, since you brought up speed, but that's not a great way to answer a question.

I have using the Wire library on an Arduino UNO at I2C bus rate of 100kHz and it's worked fine for my needs. I got bytes in and out.

At this point, the best suggestion I'd have is that if one of the above libraries you listed does not support a feature you'd like, fork it, and add support for your feature yourself. If you're only transmitting to one slave device, then you shouldn't need to worry about bus arbitration, like the TinyWire does. Adafruit is okay for the most part, but they seem (to me) slow to fix bugs and maintain code. But don't let the code's age get to you. I2C was created back in 1982, and you're still using it... :-P

Here's how I would approach choosing a library:

• Define features you need
• Look for a library which has most of those features
• Add any new features you need
• Possibly share your added features with the community with a Pull Request

Answer 2

bHogan seems to be the original developer of TinyWireM and TinyWireS. Andreas Spiess ("The guy with the Swiss accent") used rambo's implementation of the TinyWire library for his I2C sensor, and rambo on GitHub and bHogan on arduino.cc seem to be the same person...

I've also used rambo's TinyWire library, and managed to make it work. Adafruits version of TinyWire seems to be a fork of rambo's code.