Using i2c With Simavr

This will run your avr program and start gdb listening on 1234 ~/simavr/simavr/run_avr -m attiny85 -f 8000000 -g ~/Projects/attiny85-example/build/main.elf

> file main.elf
> target remote :1234
> load

to set a break point

> b loop
> c

Use these commands to display variables every break point > display state > display /t PORTB > display /t PINB

Using i2c with avrsim

The example in board_i2c uses the i2c_eeprom library provided to operate as a simple read and write source.

// initialize our 'peripheral', setting the mask to allow read and write
i2c_eeprom_init(avr, &ee, 0xa0, 0x01, NULL, 1024);
i2c_eeprom_attach(avr, &ee, AVR_IOCTL_TWI_GETIRQ(0));
ee.verbose = 1;

Then in the firmware they write to the eeprom as a secondary i2c device. The way it works is that when the the start address is in write mode, the eeprom device waits for two bytes to define an internal pointer to where to write the data.

In this case we start with the write bit set so the eeprom will wait for the pointer to be received: 0x01AA.

i2c_start(EEPROM_ADDR + I2C_WRITE);
// eeprom address, in little endian

We then send bytes and the eeprom records them until it recieves stop.


Then we send start again and send a new pointer index of 0x01A8, 2 bits less than our initial starting position (representing 2 bytes).

i2c_start(EEPROM_ADDR + I2C_WRITE);

Finally we start a third time in read mode and this triggers the eeprom device to begin writing bytes starting that that position and increasing after that. Subsequent reads read 0xD00D until the stop command is issued.

i2c_start (EEPROM_ADDR + I2C_READ);
for (uint8_t i = 0; i < 8; ++i) {