pySerial - how to open port

[theoffi...@gmail.com]

Hello everyone.
I would like to use web2py as my Raspberry Pi webserver. i need to send some serial data from the web application to Raspberry Pi and send to a device. However, i encountered the error of " <class ‘serial.serialutil.SerialException’> could not open port /dev/ttyAMA0: [Errno 13] Permission denied: ‘/dev/ttyAMA0′ "

I have been stuck at this for weeks and i can't seem to find any solution except moving on to using cherrypy and jquery. :( but i really wish to use web2py!

So, i have this code below that could work fine using normal python script as well as cherrypy. in web2py, i put this under "default.py" and create a new def for it.

import serial
import time

serialport= serial.Serial ("/dev/ttyAMA0", 9600, timeout=0.5)
serialport.write("\x03LI1234\x0D")
response=serialport.readlines(1)
print response
time.sleep(1)

what could have been done wrongly? :(

Read more details here: http://yvonnezoe.wordpress.com/2013/03/14/web2py-web-app-progress/

[Niphlod]

there's no way that a module running on cherrypy doesn't work under web2py.
Seems a permission problem, so you need to start web2py with the same user you're using for making that work with cherrypy.

[Rufus]

Perhaps it is already open by another process?

I'm not a major linux user (yet) but in windows only one process can open the serial port at a time.  Perhaps
"Permission denied" is the same as "In use".

Also make sure you close it when, if your application doesn't terminate, as web2py doesn't, depending where
and how you opened it.

[Joe Barnhart]

I think Niphlod is right. You need to add your user to teh "dialout" group.

http://dereenigne.org/linux/debianubuntu-serial-port-access

--Joe

[theoffi...@gmail.com]

hmm, i used the exact same code for both cherrypy and web2py which is as mentioned above...

[The Organisation of Secret Shoppers]

I see... but how should i close the serial port opened by another application? does shutting down the whole system close it? initially, i created a normal python script just to communicate with the device through the serial port. it succeeded. so i moved on to web2py but perhaps i missed out something or use the wrong coding which led me to that error. i'm not really sure where should i put things but i created a new def "test" function and a default/test.html...

attached is the w2p packed file.

without doing anything to the python script, i installed cherrypy and wrote a simple web app to test the communication and it worked. so i doubt may be there is something wrong in my coding somewhere. :( i have added the user to the dialout group too.

sudo usermod -a -G dialout pi
sudo usermod -a -G dialout www-data

the result is still the same... 

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[Niphlod]

you need to take into consideration what changes between the web2py environment and the cherrypy one.
assuming that you start cherrypy with something like this in a mywebserver.py

import cherrypy
class HelloWorld(object):
    def index(self):
        return "Hello World!"
    index.exposed = True

cherrypy.quickstart(HelloWorld())

and do python mywebserver.py to start it, a very few things change between that process and the one you get doing
web2py.py -a yourpassword

with your app.
are you starting web2py this way or is it "mounted" under apache ?

[The Organisation of Secret Shoppers]

my web2py is forever "on". when i switch on my Raspberry-Pi, the web2py server is alive and i can access the webpage from another comp in the same network.

Btw, thank you so much for your patience and help. :) It seems to work suddenly which i still could not figure out why! :/

just that i'm still stuck at mapping URL, writing arguments and things like that. Is there any site with good complete examples? i couldn't digest the web2py manual without matching examples :(

[Niphlod]

clearly it was due to a permission problem.... btw, if you don't need apache for anything else, given that the raspberry has "limited" resources it would be better to stick with web2py's "embedded" webserver rather than having it mounted on apache.

[The Organisation of Secret Shoppers]

by that, do you mean to start the webserver by typing python web2py.py in the terminal?

thanks a lot! :D

[Niphlod]

yep, it should be less of a "memory hog" hungry on system resources.
BTW, I have a raspberry too, but I never manage to find time to play with it.

[The Organisation of Secret Shoppers]

i see. sounds like a better plan :)

haha i think this little raspberry pi is quite amazing! :D i have never encounter linux or other programming language (other than c++) till i met R-pi. and i start  to enjoy learning them :)))
thanks again!!