Rosserial help

edit

There is something wrong. I have no idea what. Anybody who knows what this is willing to help?

Here is the code from the arduino:

#include ros.h
#include <std_msgs/String.h>
#include <std_msgs/Float64.h>
#include <sensor_msgs/Imu.h>

ros::NodeHandle  nh;

sensor_msgs::Imu data;
ros::Publisher p("imu", &data);

char frame[] = "/imu";

int xPin = A0;
int yPin = A1; 
double xValue = 0;
int xValueRaw = 0;
double yValue = 0;
int yValueRaw = 0; 

void setup()
{
  nh.initNode();
  nh.advertise(p);
}

void loop() {
  // read the value from the sensor:
  xValueRaw = analogRead(xPin);   
  xValue = (((xValueRaw *  0.0049) - 1.66) / (0.312)) * 9.80665; //convert to m / s^2
  yValueRaw = analogRead(yPin);
  yValue = (((yValueRaw *  0.0049) - 1.66) / (0.312)) * 9.80665; 
  //convert to volts<

  //now, we publish the m/s^2 acceleration to ROS. 

  data.header.frame_id = frame;
  data.orientation_covariance[0] = -1; //tells ROS  to ignore the orientaiton of the data (not provided)
  data.angular_velocity_covariance[0] = -1; //tells ROS to ignore the angular velocity of the data (not provided)
  data.linear_acceleration.x = xValue;
  data.linear_acceleration.y = yValue;
  data.linear_acceleration.z = 0; 

  data.header.stamp = nh.now();
  p.publish(&data);
  nh.spinOnce();
  delay(250);
}

I chose a low publish speed just for the purpose of checking that I'm getting something. Unfortunately, rosserial is giving me this:

turtlebot@Turtlebot_0356:~$ rosrun rosserial_python serial_node.py _port:=/dev/ttyACM0 _baud:=4 
[INFO] [WallTime: 1332888473.566842] ROS Serial Python Node
[INFO] [WallTime: 1332888473.582473] Connected on /dev/ttyACM0 at 4 baud
Traceback (most recent call last):
  File "/opt/ros/electric/stacks/rosserial/rosserial_python/nodes/serial_node.py", line 56, in <module>
    client = SerialClient(port_name, baud)
  File "/opt/ros/electric/stacks/rosserial/rosserial_python/src/rosserial_python/SerialClient.py", line 242, in __init__
    self.requestTopics()
  File "/opt/ros/electric/stacks/rosserial/rosserial_python/src/rosserial_python/SerialClient.py", line 246, in requestTopics
    self.port.flushInput()
  File "/usr/lib/python2.6/dist-packages/serial/serialposix.py", line 358, in flushInput
    raise portNotOpenError
serial.serialutil.SerialException: Port not open

I am not sure why it doesn't like me, but it really doesn't. I don't know how baud rates work, so I chose 4 because it should send 4 messages in one second. Please help!