I2C receive handler, as seen on I2C for Arduino

Question

When managing smbus/I2C devices using python with the RPi, is there a way to register a handler function so it is called when a byte is available for read, like in Arduino Wire.onReceive()?
Otherwise, is the only way to do this to read periodically from the device (and handle the exception that is thrown if there is nothing to read)?
Thanks!

Answer 1

The Raspberry Pi I2C drivers only support master mode (i.e. the Pi initiates all I2C transactions).

There is no point in a Wire.onReceive method as the Pi does not accept unsolicited messages.

EDITED TO ADD

Some I2C devices have interrupt lines. If your device does then this could be connected to a Pi gpio and could be used to trigger a Pi I2C transaction.

EDITED TO ADD

I thought the Raspberry Pi's I2C implementation was well documented. Apparently it isn't or I can't find it.

For I2C see http://en.wikipedia.org/wiki/I%C2%B2C

Do a search for raspberry pi acting in slave mode. There are no implementations.

Answer 2

This is in C, and I'm not promising it will get you what you want (see joan's comments below), but it does meet this criteria:

is there a way to register a handler function so it is called when a byte is available for read

If you use the native i2c-dev, ioctl() based interface, you get a regular file descriptor. You can then use regular old POSIX low levelread() and poll(), etc. The later is useful in implementing call back functions.¹

More information at:

• https://www.kernel.org/doc/Documentation/i2c/dev-interface
• https://www.kernel.org/doc/Documentation/i2c/smbus-protocol

You may want to go through other things in that directory (Documentation/i2c/) but that's the best place to start. It's the same path as in a kernel source tarball, if you have one of those.

I've used the native userland interface via C and C++ quite a bit with a bunch of devices. The only caveat I have is that some of them respond better to plain read() and write() than to the i2c_smbus_ functions; if at first you don't succeed try the same thing only different.

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^{1. If you don't know how to implement a callback with poll(), it is a fairly common practice but you may need a separate thread. If you just want to wait for other stuff at the same time and handle events as they happen, a single thread is ok; if you want to do unrelated things at the same time, that requires multiple threads.}