QNX iPAQ Hardware Requirements

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An Introduction to Embedding with the iPAQ

This topic will explain what it means to embed an operating system into a device. This includes a brief discussion about what the installation process is actually doing to your iPAQ. Feel free to read this if your unfamiliar with terms such as burning, flashing, images or bootloaders.

Introduction

The iPAQ Reference Platform demonstrates how you can embed the QNX operating system into Compaq's iPAQ handheld device. The complexity of developing an embedded device can vary greatly depending on your hardware, your operating system and the tools at hand. Luckily, this device is affordable, accessible, durable and directly relates to the embedded industry. QNX offers a wide variety of professional tools, but with the iPAQ Reference Platform and a simple terminal program, you can explore embedding your own system.

The remainder of this document will give you a feel for embedded development, using the iPAQ as a model. If you're just looking to play around with QNX (and don't want to know the how's and why's) feel free to skip to the next section.

The iPAQ Hardware - Feature Notes

Before you begin doing any embedded development, you should be aware of the limitations and purpose of the hardware built into your device. The iPAQ is no exception. It contains a powerful processor with many components, yet there are features and limitations which may effect your projects:

The iPAQ contains anywhere from 16 to 256 Mb of internal DRAM. This is similar to the memory used in a conventional PC.
The iPAQ contains 16 to 32 Mb of internal flash. Flash is nonvolatile memory, which means when the device is powered down, the data it contains will not be lost. Flash has its drawbacks, it is significantly slower than conventional RAM and cannot be used indefinitely. Rewriting over a flash card will eventually "burn out" the data on the card, although this occurs only after thousands of writes.
The iPAQ can access external peripherals via two types of interfaces: PCMCIA or Compact Flash. Both networking and additional storage are commonly added through an expansion card. QNX recognizes flash expansion cards and micro drives although they may need to be initialized via the dinit utility.
The iPaq is using a 200Mhz Intel ARM processor, which lacks a floating point unit. This means that software which use precision numbers (floats) will run much slower than integer based software.
The iPAQ has a serial port on the bottom of the unit which is used to reload its nonvolatile flash. This process is commonly called flashing the device. To install the iPAQ Reference Platform you will have to flash your iPAQ with the QNX image. After you are done installing, you may access a login prompt through the serial connection and log into the root account, without a password.
The iPAQ's preferred input is through the user of a touch screen. Unfortunately, touch screens tend to 'float' or adjust over time, due to temperature fluctuations and everyday usage. As a result you must calibrate it the first time you boot your device. In an emergency, you can manually remove the calibration files from /system/data/calibration and reboot your device to recalibrate.
The iPAQ has a beautiful liquid crystal display. Unfortunately, the light which causes the brightness of the screen draws a lot power. The iPAQ Reference Platform automatically turns off the backlight if you are not using the touch screen to conserve your battery. It is also important to note that although the iPAQ can display thousands of colors, it does not display the same thousands of colors you might see on your conventional PC. It has 12-bit display with only 4 bits of red, green or blue.
The iPAQ has a power button, which causes the device to power down. With this release it does not retain the state of the device and will cause you to reboot when you turn the device back on. The Intel ARM processor supports a number of power management features, but the demonstration software included in the Reference Platform does not fully implement advanced power management.
The iPAQ has ten multi-purpose buttons, all of which are handled by a button manager. The manager relays the button presses as keyboard events to the active application. The iPAQ hardware does not allow the button to be notified if more than one button is pressed down. This includes the directional pad and any other buttons.
The iPAQ has a speaker and a microphone. The iPAQ Reference Platform contains a rudimentary sound player which plays raw audio in the .ub format.

Ok, so that's a quick look at your hardware. Now let's look at how the iPAQ moves from an inert piece of technology to an interactive QNX research tool!

The iPAQ Startup Process

When the iPAQ is turned on, the ARM processor begins the boot sequence by transferring control to a "boot loader". This is code which was installed into the device's flash memory when it was being made. Once the loader is activated, it collects information about the hardware and prepares to start the operating system.

Compaq has be gracious enough to release an improved bootloader which displays an initial splash screen and is capable of booting the QNX operating system, with a little help. The bootloader is interactive; it talks over the iPAQ serial port at the baud rate of 115200. You can issue commands to this bootloader and it may save settings back to flash. The loader may also receives uploaded data using the XModem protocol.

To install the QNX operating system, two files are copied into flash via the boot loader: the image file system (ifs) and the extended file system (efs). As you will see, the ifs is a small file which contains the next crucial components for booting the iPAQ and the efs has all the large pieces which define our demonstration environment.

Once the boot loader has configured the device, it begins to look for an operating system to boot. The ifs should have been installed into a specific place in memory, otherwise the boot loader will output an error message out the serial port, confused. If all went well, the bootloader begins to transfer control to a tiny piece of code which has been appended to the front of the ifs. This code, written by QNX, is called the initial program loader (ipl).

The ipl does the work to get the actual operating system up and running. It looks at the ifs and begins copying and executing the QNX startup code into DRAM. Control is now passed to startup which decompresses the kernel and the remaining portion of the ifs into DRAM. At this point, the QNX operating system is actually functional.

The kernel begins processing its first initialization script contained in the ifs and the machine begins to really take off. There are now files and a file system to allow the remainder of the device to be functional. First, the serial and the flash drivers are loaded. This allows the efs flash file system to be mounted at root (/).

The contents of efs is what makes up the user environment and acts as a hard drive to store any data you might create as you use your device. In this case, the Photon graphical environment is installed in the usual UNIX directories, like /usr/lib and /usr/bin while some iPAQ-specific software has been placed into the directory, /system. This directory is just an arbitrary place where the ipaq environment can live.

Now that all of your resources have been mounted and the device's peripherals are accessible, the drivers and system services can be started. The script /etc/init runs all the basic services available in the efs.

Summary

At this point, you should generally understand what it takes to boot an embedded device. Continue on to install the iPAQ Reference Platform. The hands on experience is a great starting point for new developers and delivers a practical environment for even experienced engineers. QNX encourages its customers and partners use this environment to experiment with the ARM processor, and to demonstrate their products running on the QNX operating system. QNX also hopes that students and casual developers become interested in embedded development with QNX and join the QNX developer community.

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