Serial Receiving from Arduino to Raspberry Pi with PySerial stops after a while

Question

I'm working on a project in which I have to receive some 25 character data at a time in order to process it in Raspberry Pi. Here is the example code that generates some data I want to receive from Arduino:

char i =0;
char  a =0;
char b=0;


void setup(){

 Serial.begin(9600);
 for(i=0;i<25;i++){

    Serial.print('l');}
    Serial.print('\n');
    delay(2000);
}


void loop(){

 for(i=0;i<25;i++){
     for(a=0;a<i;a++){
      if((a==9)||(a==19)||(a==24))
          Serial.print('l');
      else
          Serial.print('d');   
     }
     for(b=0;b<25-i;b++){
          Serial.print('l');
     }


     delay(2000);
  }
}

It sends a line like this 'llllddddllldddd...' This line is 25 characters length. Now, I want to receive this with Raspberry Pi. Here is the code I'm trying to work:

ser = serial.Serial('/dev/AMA0',9600,timeout=1)
ser.open()

try:
   serial_data = ser.readline()
   print serial_data
except serial.serialutil.SerialException:
   pass

This code receives data very correctly for like 5 seconds, and then suddenly stops receiving.

Moreover, when I try the following, I get no output, or Input/output errors.

serial_data = ser.readline()
print serial_data

EDIT1: Okay, I commented the exception now. It gives the following error:

 raise SerialException('device reporst rediness to read but returned no data (device disconnected?)')
serial.serialutil.SerialException: device reports readiness to read but returned no data (device disconnected?)

What is the correct way to receive a 25 character data from arduino into raspberry via PySerial? Any help will be greately appreciated.

Answer 1

I had the same problem and was breaking my head for a good time, try this

Run

ps -ef | grep tty

If the output looks anything like

root      2522     1  0 06:08 ?        00:00:00 /sbin/getty -L ttyAMA0 115200 vt100

Then you need to disable getty from trying to send data to that port

In order to use the Raspberry Pi’s serial port, we need to disable getty (the program that displays login screen) by find this line in file /etc/inittab

T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100

And comment it out by adding # in front of it

#T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100)

To prevents the Raspberry Pi from sending out data to the serial ports when it boots, go to file /boot/cmdline.txt and find the line and remove it

console=ttyAMA0,115200 kgdboc=ttyAMA0,115200

Reboot the Raspberry Pi

Credit where credit is due: http://blog.oscarliang.net/raspberry-pi-and-arduino-connected-serial-gpio/ helped me figure out how to diable getty