AVR Freaks

Hi clawson, thanks for the reply. Yes, I generated an Atmel Start project & went through the code when creating my polled version - it's like wading through pea soup, but it was how I got the commands that I have.

In the Atmel Start code there are functions like:

static i2c_fsm_states_t I2C_0_do_I2C_RX(void)
{
	I2C_0_status.addressNACKCheck = 0;

	if (I2C_0_status.data_length == 1)
		TWI0.MCTRLB |= TWI_ACKACT_NACK_gc; // Next byte will be last to be received, setup NACK
	else
		TWI0.MCTRLB &= ~(1 << TWI_ACKACT_bp); // More bytes to receive, setup ACK

	if (--I2C_0_status.data_length) {
		*I2C_0_status.data_ptr = TWI0.MDATA;
		I2C_0_status.data_ptr++;
		TWI0.MCTRLB |= TWI_MCMD_RECVTRANS_gc;
		return I2C_RX;
	} else {
		*I2C_0_status.data_ptr = TWI0.MDATA;
		I2C_0_status.data_ptr++;
		I2C_0_status.bufferFree = true;
		switch (I2C_0_status.callbackTable[i2c_dataComplete](I2C_0_status.callbackPayload[i2c_dataComplete])) {
		case i2c_restart_write:
		case i2c_restart_read:
			return I2C_0_do_I2C_DO_NACK_RESTART();
		default:
		case i2c_continue:
		case i2c_stop:
			return I2C_0_do_I2C_DO_NACK_STOP();
		}
	}
}

and

static i2c_fsm_states_t I2C_0_do_I2C_DO_NACK_STOP(void)
{
	TWI0.MCTRLB |= TWI_ACKACT_NACK_gc;
	TWI0.MCTRLB |= TWI_MCMD_STOP_gc;
	return I2C_0_do_I2C_IDLE();
}

which, as far as I can see, are the same as what I've done. Incidentally, I could not get I2C communications with the Atmel Start code working at all for me, hence rolling my own code, which at least does work if I comment-out the polling.

Hi trevorg, thanks for posting your code - interesting that you poll RIF bit being unset at the beginning of your write function, whereas I am polling for it being set at the end of my read function. There must be some way of checking that the read command has been completed... At this point I think I'll just give up on trying to get the polling to work correctly, and just disable the checking of the RIF bit altogether - the read function seems to work without it for my use case.

Just for interest, my TWI control register initialisation code at the start of a TWI operation is:

TWI0.MCTRLA = 1 << TWI_ENABLE_bp      // Enable TWI Master: enabled
            | 0 << TWI_QCEN_bp        // Quick Command Enable: disabled
            | 0 << TWI_RIEN_bp        // Read Interrupt Enable: disabled
            | 0 << TWI_SMEN_bp        // Smart Mode Enable: disabled
            | TWI_TIMEOUT_DISABLED_gc // Bus Timeout Disabled
            | 0 << TWI_WIEN_bp;       // Write Interrupt Enable: disabled

TWI0.MCTRLB |= TWI_FLUSH_bm;
TWI0.MSTATUS |= TWI_BUSSTATE_IDLE_gc;
// Reset module
TWI0.MSTATUS |= (TWI_RIF_bm | TWI_WIF_bm);

TBH I would have happily used the Atmel Start code if it had just worked, but sadly it didn't and trying to debug that code with all of its data structures and callback routines and function pointers was way more difficult than just rolling my own implementation. It's a shame there's no application note for TWI/I2C on the ATtiny814, because that would have been useful. Oh well.