For simulation type command like:
iverilog -o qqq i2c_slave.v test_i2c_slave_tx.v		// FOR TX TO SLAVE
iverilog -o qqq i2c_slave.v test_i2c_slave_rx.v		// FOR RX FROM SLAVE

Then type command:
vvp qqq

And open out.vcd with gtkwave
