GNU/Linux and the Sony Ericsson K750i

Overview

These pages are conceived to keep hold of the experiences and discoveries I made with this phone in its interaction with my linux systems.

• Creating themes: Taking a look at the theme files and their creation with basic Linux tools
• Remote Control: Controlling Linux with the Bluetooth remote control
• Accessing the phone
  • File transfer: How to copy files from your computer to your phone and vice versa
  • The filesystem: Exploring the directory structure on the Memory Stick
  • Controlling the phone with the computer: Accessing the GSM modem via a serial line
    • AT commands for the K750i: Controlling the phone and creating custom user interfaces
    • DisGUISE: A C# class library for the Sony Ericsson AT interface
• Tricks and Hints

File transfer

To transfer ringtones, images, themes or any other file to your phone, you have basically three options:

• Grab the memory stick from the phone and insert it into your card reader
• Use the USB cable to access the integrated memory stick
• Use Bluetooth to beam the files towards your device

The first two methods access the storage directly without involving the cellphone software.

stefan@nano:~$ hcitool scan
Scanning ...
        00:12:EE:12:34:56       K750i

#!/bin/sh
# Register OBEX PUSH
sdptool add --channel=10 OPUSH
# Launch OBEX server
obexserver

The filesystem

The filesystem on the memory stick contains a directory structure that reflects the multiple uses of the storage medium:

• dcim/ does contain the pictures taken with the integrated camera
• mp3/ contains sound files which are accessed by the mutlimedia player and can be used as ringtones
• mssemc/ Those files are related to the phone itself, the name may be an abbreveation for "memory stick sony ericsson media card" (just a wild guess).
  • Media files/
    • audio/
      • ringtones/
      • videodj/
    • image/
    • other/
    • theme/ Theme files have to be placed here in order to be recognized by the phone software
    • video/
    • webpage/

Although MP3 files on the Memory Stick can be used to signal an incoming call, the sound file for message notification has to reside on the buitin phone memory. So if you want to use a custom sound for it, you have to copy or move the file with the file manager to this integrated storage.

Controlling the phone with the computer

The cellphone offers an (virtual) serial interface that can be used to issue AT commands or trigger other phone functions. The serial line is accessible via the USB cable, as well as via Bluetooth. Once the link is established, you can access the data of the phone, interact with the user interface and manipulate the telephony functions. See my page about various AT commands for more information.

Serial interface via USB

Once you plug in the phone, your Linux system not only recognizes the USB storage device, but also detects the builtin modem. It then should load the appropiate cdc_acm module which brings support for USB modems and ISDN adaptors.

Depending on your DevFS or udev configuration, the new device will be placed under /dev/ttyACM0 and /dev/ttyACM1; consult your logfiles to investigate this. The files can be opened with minicom or any other terminal program, some other programs like xgsm also use this interface to gain access to the phone.

Serial interface via Bluetooth

Instead of relying on a wired connection, you can also use the Bluetooth interface to access this serial line: An easy way to achieve this involves the automatic binding features of the rfcomm daemon. Simply include the following section in the file /etc/bluetooth/rfcomm.conf:

rfcomm0 {
    bind yes;
    # MAC address of your phone:
    device 00:12:12:34:56:78;
}

Now reload the Bluetooth subsystem with /etc/init.d/bluetooth restart. If you already paired your computer with your phone, accessing the device /dev/bluetooth/rfcomm/0 (The exact location depends on your /dev setup) will instruct RFComm to connect to the phone without any user action needed. You can monitor the process with the rfcomm utility:

stefan@nano:~$ rfcomm 
rfcomm0: 00:12:12:34:56:78 channel 1 clean

Once a process opens the device file /dev/bluetooth/rfcomm/0, the RFComm daemon contacts the phone:

rfcomm0: 00:12:12:34:56:78 channel 1 config [tty-attached]

which results in

rfcomm0: 00:12:12:34:56:78 channel 1 connected [tty-attached]

Once the device file is closed again, the connection is terminated.

Tricks & Hints

These are some tricks that are not linux specific, but interesting:

Service menu

To access the service menu, where you can retrieve some information about the running firmware and check the phones hardware, pull the following button stunt:

• Move the joystick to the right
• Press *
• Move the joystick to the left twice
• Press *
• Move the joystick to the left once again
• And press * another time