I²C-Lib

Make 8-Bit AVR devices more versatile. Build your own special sensor or actuation controller, connect multiple master devices to common I/O or even communicate by I²C instead of UART. Check out the I²C operation modes supported:

• Slave
• Single Master
• Multiple-Master
• Multiple-Master-plus-Slave

The Multiple-Master modes all feature bus arbitration in case of simultaneous accesses.

Use hardware modules on the micro, dedicated to I²C support:

• USI
• TWI

Make hardware support transparent to the application. One application could compile for different micros without changes to the source code - at least for the I²C parts! For example a simple master application currently compiled for an ATtiny2313 can be compiled for an ATmega48 by just changing some Makefile settings. Of course, environment changes (e. g. LED or pushbutton connections) need to be reflected, too.

Currently verified with:

• ATtiny2313 (USI)
• ATmega168 (TWI)

Prepared already for:

• ATmega8 (TWI)
• ATmega48 (TWI)
• ATmega88 (TWI)
• ATmega328 (TWI)
• ATtiny26 (USI)
• ATmega169 (USI)
• ATmeag16U4 (TWI)
• ATmega32U4 (TWI)

In theory those should immediately work, but this is still not verified. Micros not listed just lack their appropriate definitions and can get added in lib-i2c/includes/i2c_hw.h.

The ATmega8 is somewhat special since it lacks a TWIMASK register. Due to this it just cannot be made to respond to an entire address range.

What To Find Where

The Library itself is contained below the path lib-i2c/. You find there its includes and sources in case you want to take a look under the hood. Normally you do not need to bother with its details. The only file of interest is lib-i2c/includes/i2c_hw.h giving all the API interface details.

Demo applications are prepared for the variety of operation modes the I²C is capable of. There are quite a couple and each is put into a dedicated folder:

• single-master-demo/ - one single master accesses two slaves
• multi-master-demo/ - two master devices access one common slave
• multi-master-slave-demo/ - two master devices access one common slave and also each other as slave

Each demo contains documentation on the circuitry intended, the application source code and the makefiles used to build this particular demo. Be aware, the demos are made to compile once for different settings on different micros. For this reason most demos are way more complicated to build than your later application code. But no fear, the complicated building is done by make. You simply call make on the command line to rebuild the examples. Ready to flash .hex-files are pre-made for you. Just flash them to the micros and hook the hardware up according to the schematic to try it out.

In most cases your project will compile just for one certain setting using one micro. For this you just need one makefile and one main.c file.

It is recommended to use the folder structure as it is given here. It clearly distinguishes between lib parts, application and the top level used for some management and documentation purposes.

How To Use

Well, this is quite simple. Take all files found in /lib-i2c/, add them to your project and compile them together with all the other things. Of course, your makefile needs to get all files referenced for compilation.

See the demos for some examples. Be aware, that most demos provide code for two different AVRs. Because if this you will find one ...usi... and one ...twi... set of files that need to get flashed into the right controller.