Getting Started with the Trolltech Greenphone SDK

Trolltech recently released many smartphone developers' dream combination—the Linux-based Greenphone and its open-source Qtopia Phone SDK.

The Trolltech Greenphone is a full-featured tri-band GSM (900/1800/1900MHz) mobile phone with a built-in 1.3 megapixel camera. Like many other modern smartphones, it features a QVGA touchscreen, Bluetooth, client USB, mini-SD Flash and stereo audio connectors.

Under the hood, it is built around a Marvell 312MHz PXA270(ARM) processor, runs with 64M of RAM, and has 128M of built-in Flash storage. It also uses the same field-proven Broadcom BCM2121 GSM/GPRS baseband processor module as the Palm Treo.

The Greenphone almost could be described as a sporty, Linux version of the Palm Treo. It is much lighter, more compact and comes in any color you want—as long as it's green!

The Greenphone SDK is a distribution of Qtopia Phone Edition, specially configured for use on the Greenphone. Qtopia (formerly Qt Embedded) inherits its API from Trolltech's flagship product Qt, a mature C++ application framework available for Linux/X11, Windows and Mac OS X. Qtopia is specifically enhanced for embedded Linux devices, such as phones, PDAs and appliances.

Qtopia is remarkably self-sufficient—sitting immediately on top of the base operating system, it provides its own font and image rendering, window management and input processing. Along with this sort of behind-the-scenes stuff, Qtopia avails itself of all the rich features of Qt's standardized access to files, networking, multithreading, internationalization, graphics processing and, of course, GUI widgets.

Like its big brother, Qtopia is readily available either as a free download to those wanting to do GPL-style open-source development or by commercial license purchased from Trolltech.

Qtopia also bundles a suite of personal information management tools as would be expected on any PDA or smartphone.

When you open the Greenphone's box, you find everything needed to start developing: mobile handset, power supply, USB cable, stereo headset and a Greenphone SDK CD-ROM. This last item contains a copy of the VMware player and a virtual machine preloaded with Debian Linux, Qt, Qtopia, KDevelop, native development tools and a complete ARM cross-compiling toolchain.

Figure 1. Greenphone Package Contents

The only other item needed actually to go on air with your newly created applications is a GSM subscriber identity module (SIM) card with a currently active account.

The two most widely used standards for cellular communications are GSM and CDMA, with GSM outnumbering CDMA worldwide by a ratio of about 1 billion to 270 million users. Although they are as completely incompatible on each other's networks as AM and FM radio, a normal user typically would notice only that phone accounts on GSM phones are usually tied to the SIM card, so changing handsets is really easy.

GSM currently stands for Global System for Mobile communications. It is an open standard governed by the nonprofit European Telecommunications Standards Institute (ETSI). GSM allows great interoperability permitting easier international roaming. GSM's other claims to fame are higher digital voice quality; a cheap short messaging service (SMS); multimedia messaging service (MMS) for exchanging images, audio, video and rich-text data; and finally, a general packet radio service (GPRS), often used as an Internet gateway, with billing based on megabytes of data transferred, as opposed to time spent on-line.

The Greenphone actually is based on two ARM RISC processors: a beefy Marvell 312MHz PXA270 acts as the PDA part and communicates to the ARM7-based GSM/GPRS communications controller. This controller is effectively the heart and brain of the phone component. It also acts like a modem and accepts GSM AT-style commands to dial, answer calls, send or receive messages, and other activities typical of a GSM/GPRS communications device.

Standard GSM modem AT commands can be sent to the phone, which execute and then return a response code. These AT commands are analogous to the decades-old Hayes modem commands, but instead of user using or programming a string like “+++ATDT16505511676” to dial Trolltech's number 1-(650) 551-1676, we do the same sort of thing with the GSM version of the command set, and the string looks more like “ATD16505511676”.

There are myriad other AT commands for handling everything that the GSM/GPRS phone unit can do. These include setting up the phone and establishing various types of communication, such as voice calls, SMS and MMS, and they can be used for getting information on signal strength, network status and so forth.

For a comprehensive description of these standardized commands, you can download the following documents from the ETSI site:

Qtopia embeds the most commonly used of these commands into C++ class wrappers. The on-line documentation in Qt Assistant describes how to use and enhance these classes in the sections titled “GSM Modem Integration” and “Modem Emulator”.

For testing applications off-line, the Greenphone SDK provides a modem emulator that allows testing software without having actually to join a network and go on air.