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EMBED THIS PC

PART 2: Emulator and EPROM Basics
by George Martin

Start ı Making The Choice ı Getting The Debugger Going ı Putting It All Together ı Sources and PDF

MAKING THE CHOICE

Before I select an emulation plan, I want to look into the CPU a bit more. First, Iım going to assume the CPU is in a surface-mount package, which I think is reasonable. Because there are 250ı400 pins, finding a connector that lets me remove the CPU and plug in an emulator will be difficult at best.

Second, Iım assuming that Iıve selected a highly integrated device. If I apply power and a clock, all I need is memory and an LED or serial port to determine activity. The CPU is permanently attached to the board and, with power and a clock, itıs going to run.

Given these assumptions, I think an EPROM emulator is a good choice for my embedded ı486 project. The development plan: write code, transfer it to the EPROM emulator, and reset the CPU using the EPROM emulator. The unit should then run the code I loaded.

LAYING OUT THE TOOLS

Now that some of the peripheral issues are covered let me look more closely at the CPU. I found two classes of devicesıthose intended for desktop or laptop systems and those intended for a more minimal existence. If you need desktop or laptop characteristics, then use the first type of CPU.

Iım focusing on the second group. I need to consider floating-point support (FPU), L1 and L2 cache, the bus interface, and speed. Iım going to use the AMD ELAN series of embedded devices, which consists of the SC300, SC400, and the just- announced SC500. These devices incorporate a lot, and I mean a lot, of the support circuitry from the desktop design into the more minimal, embedded CPU.

The SC300 family is a ı386 machine, the SC400 is a ı486, and the SC500 matches the Pentium. Each device uses different supports, which are built into the chip. For example, serial, parallel, DMA, keyboard, and LCD controller are built into these devices. Others have a FPU and PCI bus interface. Check AMDıs web site for a more complete overview (www.amd.com/products/lpd/32bitcont.html). You can get a list of their evaluation boards at www.amd.com/products/lpd/prodsupp/20071.html. And, vendor support is available at www.directories.mfi.com/embedded/amd-e86/. Keep in mind that if you select a different device for your project, most of the vendors and their products are applicable in some form.

The Elan family ranges from ı386 to ı486 without FPU and to ı586 with FPU. Clock speeds range from 25 to 133 MHz, and interfaces range from simple I/O to PCI support. I think you should be able to find a solution that fits your price/performance requirements.

In the web pages for the AMD (and other) CPUs, thereıs a list of development tools such as development boards, compilers, and emulators. I recommend finding a development board thatıs close to your design, so you can use that as the basis for your schematics and software development.

For language tools, I know I need an assembler and a C compiler. As a ı486 machine, I could theoretically use anything that runs on the desktop. Iım a big fan of Borlandıs Turbo C V.3.0 (DOS), which I use to write C code that I can debug in the PC and then compile for the target machine. Of course, you could use Microsoft Visual C++ or a host of others. Keep in mind that these compilers are 16 bit. If youıre wanting to work with protected mode, tune in next month.

A vendor that I have used in the past and one which works well with the Borland set of tools is Paradigm (www.devtools.com). Paradigm has taken Borlandıs compiler and wrapped it into an integrated environment that does the usual editing and compiling, while also offering downloading and emulation through its Remote Debug Utility. If I have a CPU running PDREM, then I can load code, single step, insert breakpoints, and examine variables. Itıs been around for years and is a stable product.

Now, for the last piece of the puzzle. Because I donıt want to burn EPROMs to transfer and test the code, the obvious solution is an EPROM emulator. Some of my customers have used these in the past and reported good results. I tried a couple of years ago without much luck (I always suspected it was my fault). To successfully embed a CPU as complicated as a ı486, I need an emulator or the combination of a remote debug and EPROM emulator. Again, there are several manufactures, but the one I selected was Grammar Engineıs Prom Ice (www.gei.com).

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