Palm OS tips and tricks
A pair of new color Palms
In contrast to recent operating system shifts on the desktop--namely Apple's move toand Microsoft's switch to --Palm's upcoming change to OS 5 and to more powerful ARM-based processors will hardly be noticeable at first, according to PalmSource software architect David Fedor. Icons and menus will look the same on most devices, and there will be no ARM-native applications to begin with, since developer tools are not yet complete.
Instead, OS 5 will rely on PACE, an emulator that delivers better performance than code running natively on the current Motorola DragonBall 68000-series chips, Fedor said. This approach means that people won't have to distinguish between software written for the newer devices and for the 22 million 68000-series Palms in circulation. "We don't want users to have to know the difference between a 68000 device and an ARM device," Fedor said.
Palm-powered devices running OS 5 will all use processors based on chip designs from the U.K.'s ARM. The processors are optimized for low-powered portable devices and are used in most mobile phones. Newerdevices also use ARM-based chips.
To make the switch easier, PalmSource developed PACE, a layer of about 80KB of code that lets 68000-series applications run normally while translating all operating system calls into ARM-native code. The result is that there is little need to upgrade legacy applications to be ARM-native, a practice PalmSource is actually warning against for now. Instead, newer hardware will simply continue to run existing software.
The software will automatically take advantage of features like high-resolution fonts and widgets if the device supports them, Fedor said. Since the operating system calls are all carried out in ARM-native code, applications written for the older OS will get the benefit of the ARM processor's higher performance. Almost all of the work done by an application will be carried out natively, Fedor said.
There are some pitfalls, though. For one thing, some applications may fail to work under PACE if they contain code that breaks Palm OS rules to get better performance, said Fedor, urging developers to clean up their code.
Certain processor-intensive operations might also work more slowly under ARM processors and have to be made ARM-native, he said.
However, "there are tons and tons of applications that run on OS 5 perfectly well," Fedor said.
The move to OS 5 and ARM will eventually mean that high-end features like double-density screens and media players are more standard across the range of Palm OS devices. The software also adds better support for security and communications.
Currently, licensees likeoffer devices with high-density screens that can play video and audio files, but the devices use graphics acceleration hardware and proprietary software extensions, meaning that applications written to use the advanced features won't work on Palm devices from other companies.
A Sony representative said that when the company adopts OS 5 it will begin using Palm's application programming interface (API) for high-resolution screens, dropping its own API.
The first release of OS 5 will not support fully native ARM applications, Fedor said. That will come with the next major release.
"You can do the switch to be ARM native when it is appropriate for your business," Fedor said. "Some companies may not see the need for several years. PACE is going to be supported for a good long time."
ZDNet U.K.'s Matthew Broersma reported from London.