THE MAGAZINE FOR COMPUTER APPLICATIONS
Circuit Cellar Online offers articles illustrating creative solutions
and unique applications through complete projects, practical
tutorials, and useful design techniques.

GETTING STARTED WITH EMBEDDED PCs

by Bob Perrin

Start ý Selecting an Embedded PC ý Hello World ý Controlling Resources ý Thank You, Intel ý Sources and PDF

After attending the Embedded Systems Conference (ESC) in San Jose, it became clear to me that embedded 'x86 products dominate the embedded-systems market.

Sure, there are still dozens of small companies making custom hardware and development tools based around other processors. For example, Parallax is still peddling the PIC-based Basic Stamp, Z-World still produces 8-bit Zilog Z180-based controllers, and Wilke has their 16-bit BASIC Tigers. Thumb through the Idea Box ads in Circuit Cellar magazine and you can still find a handful of companies selling non-'x86-based custom hardware and software. But, the 800-lb gorilla on the block is the embedded 'x86.

I have experience with all the above products and they're all fine in their respective niche, but after the ESC, I decided to broaden my horizons to include the dominant technology in the embedded-controller marketplace.

I went looking for a good how-to-use-an-embedded-PC text. I found many articles, but they were either over my head or devoid of details (or both). At long last, I found and purchased Ed Nisley's book, The Embedded PC's ISA Bus: Firmware, Gadgets and Practical Tricks [1]. This is an excellent text and I highly recommend it to anyone attempting to build ISA cards, but it still didn't fully satisfy my curiosity.

How do you get an embedded PC without a keyboard, monitor, or disk drive to boot and run your application code? How do you control the resources on an embedded PC from a C program? I decided the best way for me to answer these questions was to buy an embedded PC and tinker. After all, the best learning is accomplished by doing.

WHAT IS AN EMBEDDED PC?

The first issue to address is the difference between an embedded PC and an embedded 'x86. An embedded PC falls into a subclass of the more generalized embedded 'x86 universe.

An embedded PC should run one or more of the same OSs that a normal desktop PC runs. The development tools used to write code for an embedded PC should be the same tools used to write code for a desktop.

For example, Tern will sell you 'x86 hardware and Borland C for software development. However, Tern's products don't support DOS. So the executable image generated by the Borland tools must be handed off to a relocator written by Tern. I don't consider these products to be truly embedded PCs.

The idea of taking executable code generated by DOS-based tools for a DOS-based target system and relocating it in memory on a target system without DOS just gives me the willies.

This isn't meant to be a slap at Tern's product line, which is quite broad and successful (just check out their web site to see how NASA used their 'x86s). It's just to say that, if I'm going to use DOS tools to generate code for a DOS system, I would feel better if the target system had DOS running on it.

An embedded PC must make resources commonly found on a desktop PC available to the application-code. These resources include, at a minimum, a file system and a console. In the world of embedded PCs, the file system is often not kept on a mechanical disk. A flash memory-based or battery-backed SRAM file system is the usual storage medium. The system console is often a serial port.

In my opinion, an embedded PC need not have an expansion bus, such as PC-104 or Compact PCI, although most do sport some expansion bus.

NEXT

Circuit Cellar provides up-to-date information for engineers. Visit www.circuitcellar.com for more information and additional articles.
For subscription information, call (860) 875-2199, subscribe@circuitcellar.com or subscribe online. ýCircuit Cellar, the Magazine for Computer Applications. Posted with permission.