GM862 tutorial

The GM862 is a module that integrates a GSM modem, a GPS receiver and a Python interpreter.

The module features a file system. It doesn't support directories but it does support any files ( not just Python scripts) as long as the file names are no longer than 16 characters.

The gm862 script

Most of the tools available for the GM862 are for Windows. The archive below includes a command-line tool called gm862. The tool requires that a serial port be present and connected to the GM862. Edit ./gm862 if your serial port is not at /dev/ttyUSB0.

The script has sub-commands:

command	purpose
list	Shows a list of the files on the module
upload	Uploads all the files given as arguments to the module
rm	Removes all files given as arguments from the module
boots	Shows which script will be booted when the module is started
boot	Sets the active script that the module runs when it boots
run	Runs the active script immediately without the need for a power cycle

Examples:

$ ./gm862 help
boot
boots
help
list
rm
run
upload

$ ./gm862 list
#LSCRIPT: "Test.py",1981
#LSCRIPT: "NMEA.pyo",1364

$ ./gm862 upload Main.py

$ ./gm862 list
#LSCRIPT: "Test.py",1981
#LSCRIPT: "NMEA.pyo",1364
#LSCRIPT: "Main.py",3226

$ ./gm862 rm Test.py

$ ./gm862 list
#LSCRIPT: "NMEA.pyo",1364
#LSCRIPT: "Main.py",3226

$ ./gm862 boots
#ESCRIPT: "Test.py"

$ ./gm862 boot Main.py

$ ./gm862 boots
#ESCRIPT: "Main.py"

$ ./gm862 run

Example code

There are some other files in the archive:

HelloWorld.py  Modem.py  debug.py  traceback.py

Modem.py wraps some AT commands and provides a nice API to:

• Determine if the module is registered on the mobile network or not
• send a short message
• grab all of the short messages stored on the SIM
• delete a specified short message

traceback.py is a cut-down copy of the file of the same name from Python 1.5.2. The traceback Python module is not included on the device and is required by debug.py. debug.py provides a tidy way of sending nicely formatted debugging output but it also provides much needed support for catching and reporting exceptions on the module. Use it like this:

 
False, True = 0, 1

import SER
import MOD

SER.set_speed('4800')
SER.send("System initialization in progress..\r\n")

from debug import *
db("Debugging support is now available.")

try:
  db("Initializing modem..")
  from Modem import Modem
  modem = Modem()
  # Wait up to 15 seconds to get registered on the network:
  when_began_waiting = MOD.secCounter()
  while MOD.secCounter() < when_began_waiting + 15:
    if modem.is_registered():
      break
    MOD.sleep( 1)
  db("  registered on network: %s"% "Ny"[modem.is_registered()])
  db("  complete.")

  should_run = True
  while should_run:
    MOD.sleep( 10)

except Exception, e:
  report_error( e)

This is a considerable improvement over having the software crash with an exception and having no error output whatsoever.

Notes

• screen can be used to interact with the module. Invoke:

  screen /dev/ttyUSB0 9600

• Put the switch in the DTR HI position to automatically run the active script upon power up.
• You need not compile the Python modules yourself, which is nice because it only supports Python 1.5.2, which is hard to find for Debian. Instead, upload the .py file for the module and it will be compiled on the module when first imported ( although this can take a few seconds). It will not be re-compiled, which is good for reducing boot time in production but the .pyo files must be removed when an updated .py file is uploaded

Download

• GM862_2012-03-16.tar.gz