Chapter 2: What You Need To Know About Palm Devices

This material was published in 1999. See the free Palm OS Programming online course I developed for CodeWarriorU for some updated material.

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Hardware

Palm devices are marvels of low-power, small form-factor technology. The two AAA batteries in most models (for a thinner profile, the Palm V uses built-in rechargeable batteries instead) can last for several weeks of continuous use because of low-power components and clever power management.

The Main Processor

The main processor in the current Palm devices is the Motorola MC68328 DragonBall processor. The DragonBall is a low-power version of the MC68000 processor, a popular chip used in computers such as the original Macintosh and the Amiga. The 68328 and 68000 share the same instruction sets, but the DragonBall processor is designed specifically for the portable consumer market. Detailed information on the chip can be found on Motorola's Web site at www.mot.com/SPS/WIRELESS/products/MC68328.html.

Sidebar: Assembly Language Programming

If you're interested in writing assembly language programs for the Palm, the Pila cross-assembler is available for download from numerous sites, including www.massena.com/darrin/pilot/asdk/asdknews.htm. Please note that this book doesn't discuss assembly language programming on the Palm.

Compared to the processor in a desktop computer, the DragonBall is slow. A faster processor requires more power, and low power consumption was a primary design goal of the Palm platform. In fact, Palm Computing recommends that you offload computationally expensive processing to a desktop computer in order to save power and to keep the device responsive to the user.

The Screen

The screen on the Palm device is currently 160 pixels wide by 160 pixels high. Your application's user interface has to fit within these constraints. These dimensions may change at some point — they may get bigger. The ScrDisplayMode() function (available in later versions of the operating system) returns the screen dimensions of the current device.

A digitizer makes the screen touch-sensitive. The operating system transforms raw pen movements and taps into higher-level events (such as keystrokes) that an application can process. Your application has access to the raw events, though, and Chapter 4 shows you how to intercept them before the system processes them. Most applications just deal with the higher-level events.

Running Modes

Apart from the lower-power circuitry, the key to the Palm device's miserly ways is its power management via its running modes. A Palm device has three modes of operation:

Sleep mode occurs when there has been no user activity on the device for a certain number of minutes. The default is two minutes, but you can change the wait period to one or three minutes using the Preferences application. Sleep mode is also entered when you turn off the device using the power button. In sleep mode, the processor, screen, and most of the other hardware do not receive any power, but the memory chips, the real-time clock, and some low-level circuitry do stay powered. Pressing a button restores power to the processor and the other hardware. The real-time clock can also wake the device at a predetermined time.
Doze mode (sometimes referred to as idle mode) occurs when an application is waiting for user input. The processor is halted until a hardware interrupt signals user activity, such as the press of a button or a stroke of the pen. Most of an application's time when the device is on is spent in doze mode.
Running mode occurs when the processor is executing instructions. This mode consumes the most power, so the device returns to doze mode as soon as possible in order to conserve battery power.

As you can see, the power is never really turned off unless you pull out the batteries and let the internal capacitors (which keep the device charged while you change batteries) discharge completely. The active application is simply in a halted state when in sleep mode, ready to resume where it left off as soon as power is reapplied to the processor.

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Copyright ©1999 by Eric Giguere. All rights reserved. From Palm Database Programming: The Complete Developer's Guide. Reprinted here with permission from the publisher. Please see the copyright and disclaimer notices for more details.

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