Any hardware can give different behaviour. So if you write functions that return values, you will have some idea of where something goes wrong.

Having said that, most library code provides non-void functions, and then people choose to ignore the return values. Which is like returning home at night, and choosing not to turn on the lights. Writing void functions is like building a house with no lighting. Fine in daytime but a little difficult if someone moves the furniture.

As to your AT24C256: look in the data sheet. It has a two byte address register. You just write to the 'addrh' one before doing a 'i2c_restart'.

Compare your i2c operations with those in the data sheet.

Compare your primitive functions with those in ny bit-bang library code.

David.