Workflow

Wait for start condition from master and get transfer direction.

dir = i2c_slave_get_direction_wait(&i2c_slave_instance);

Depending on transfer direction, set up buffer to read to or write from, and write or read from master.

if (dir == I2C_SLAVE_DIRECTION_READ) {
    packet.data = read_buffer;
    i2c_slave_read_packet_wait(&i2c_slave_instance, &packet);
} else if (dir == I2C_SLAVE_DIRECTION_WRITE) {
    packet.data = write_buffer;
    i2c_slave_write_packet_wait(&i2c_slave_instance, &packet);
}