AVR Libraries
A number of libraries for AVR and using avr-gcc compilation have been developed, and are provided here under the GPL version 2 opensource licence.

I2C Master library

This library provides basic functions for performing master operations over the I2C interface (designated as the Two-Wire Interface, TWI, by Atmel). The functions provide read and write of a block (address+data) to and from a slave device. Each function initiates an operation and returns, that is, it is nonblocking. The operation is completed through interrupts and a flag is set when complete. A polling function is provided to allow the calling program to test for completion. This way the code is suitable for use with a scheduling operating system.

The library works by maintaining a read and a write buffer. The write buffer holds all data to be transferred including the address and device ID. Thus a simple device read will also involve the write buffer and a change in transfer direction will need to occur. The I2C communication works with block transactions; the master informs the slave how many bytes it wants to be sent during a read operation, and supplies a start address if the device needs one (such as an EEPROM chip). It is possible to have read only, write only and read/write (atomic) transactions. Much of the work is done in the interrupt service routine working as a state machine to interpret the bus activity. The I2C bus allows for multiple masters to contend for control of the bus. The code at this time only handles a single master.
  1. twiInit(bitRate)  Initialise the TWI interface.
  2. twiSetupTransaction(numBytes) All in and out buffer pointers are reset and the read count is set to the number of bytes to be read. If numBytes is zero, then the transaction is taken to be write only, otherwise it is read/write.
  3. twiWriteByte(dataByte) Write the next byte to the write buffer. If the buffer is full, the byte is not written. This call simply fills the write buffer and no transaction takes place. The number of bytes to be sent to the device will be the number in the queue at the time the write transaction is activated.
  4. twiLaunch(device) Launch a master transaction with a slave device. The calling program is expected to have setup the transaction by putting data in the write buffer and specifying a number of bytes to be read. If there are no bytes to
    write, the transaction is a master read. If there are no bytes to read the transaction is a master write. If there are bytes to write and read the transaction is an atomic write/read. If there is nothing to do, the function will return an error indication.
  5. twiReadByte() Read the next received byte from the read buffer. Before calling this function the calling program is expected to determine how many bytes have been received from the read transaction, and if any error occurred. The next read
    byte is returned, unless attempting to read beyond the end of the buffer whence an error indication is returned and the pointer is not incremented.
  6. twiErrorStatus() Check the error status of a transaction (whether an error occurred and its code).
  7. twiCompletionStatus() Check the completion status of a transaction (whether it completed a block transfer and how many transfers remain to be done).
References AVR libraries only:
  • BASCOM (commercial) I2C slave library
  • Keeser I2C master library (not sure if this uses TWI hardware support)
  • Fleury (GPL) I2C master library
  • Procyon AVRlib (GPL). Extensive set of libraries. I2C libraries with and without TWI hardware support
  • Efstathiou (GPL) I2C master library

A/D converter Library

This library, based on that of Chris Efstathiou, provides basic functions for A/D conversion using interrupt/polled and noise reduction sleep operations. Support for continuous operation is also provided.
  1. Single A/D conversion of one or a group of channels. This starts the conversion and returns. An ISR reads the result to a temporary location. This way either interrupt driven or polled mode can be used in the application.
  2. Free running A/D conversion. Once started the A/D converter continues to restart automatically. Channel scanning can be used, in which case all channels are scanned before proceeding to the next round of conversions. The program is responsible for picking up the results before they are overwritten. This can be useful for obtaining data at the maximum rate.
The functions are non-blocking. Once the A/D converter is started, a read  function can be used to check that conversion is complete and will return to the main program flow.

Some AVRs also have external or internal triggers for the ADC, this is not used in this library.
  1. adcInit(mode,adcClock) Initialise A/D conversion process. This function will initialise the ADC with the mode of operation and the clock rate to be used. An error will be returned if the ADC is busy.
  2. adcStart(channelMask)  Start an A/D conversion. This function will initiate an A/D conversion on a set of channels given by a
    channel mask (a 1 in each bit corresponding to the A/D channel 0-MAX).
  3. adcIsBusy() Check Progress of an A/D conversion.
  4. adcRead(channel)  Return the result of the A/D conversion. This will check if a result is ready for a given channel, and return the
    result or -1 if not available. For the AVRs the result will have a maximum precision of 10 bits.
  5. abortConversion() Abort any running A/D conversion.
References:
  • Procyon AVRlib (GPL). Extensive set of libraries, ADC library included.
  • Efstathiou (GPL) ADC library included.


First created 19 June 2007
Last Modified 19 June 2007