Do you have a question on Embedded electronics and controls? Ask our Expert, Paul Clarke

In my case, we buy a product manufactured by others and programmed by others per our spec. The device uses an ARM5 processor. We wanted to refresh and change a bunch of different things to "do it ourselves". So, on the surface, anything greater than an ARM5 in terms of feature-set, speed, etc. is better.

Other than using ther standard IO (Analogs & Digitals; I need 12 analog inputs and 8 digital inputs with 8 digital outputs), we need to have ethernet (10/100) and at least one serial port. There is no external display requirement so we won't have to worry about that.

Ultimately, think of the application as one where we are using a serial port to read/control the analogs and digitals of the proc and an ethernet port that allows the same along with a CLI and a small web server. There is more in terms of whats connecting to the analogs and digitals but until I can get this going, that part of the concept is moot. I can verify the values with a meter on the output and short the digitals to test the inputs.

I get what you are saying about the .net CF. I see that it tends to take up a lot of overhead. My concern with going with a standard C implementation is everything has to be created from scratch. For instance, if I want a simple web server, I would have to decode the HTML and then respond back per HTML standards. With a .net implementation, it can handle the actual back and forth syntax for me.

Are there C libraries available that handle that type of stuff that you know of?

Also, if we went that route, what IDE would be used for Standard C?

If we went with a WinCe implementation, does that require Microsoft licensing?

Sorry for all the questions but I am trying to rapidly wrap my head around this.

Thanks so much!

Ed

Hello Ed,

There are several ARM Cortex micro controllers which support the kind of IO and Ethernet you describe. You need to look carefully to see that the peripherals are good enough. ST, NXP and TI (Luminary) all offer potentially suitable devices. Some of the TI Cortex M3 parts have on chip ethernet MAC and PHY which can be good, NXP and ST parts need an off chip PHY.

My experience is with the Keil(ARM) tool set which is quite pricey but works. You code in C but they offer libraries for a basic real time scheduler and very basic web support. You have spotted the gap in this approach compared with .net (or similar)  - once you get into serious web serving you are going to have  a lot to do yourself. It all comes down to volumes - if you are going to make tens of thousands it may well be worth the software effort to use a cheap micro - if the volumes are low then Wince (or similar) on a bigger processor makes more sense.

I don't know enough about your application to call it one way or annother but I feel that if that web server thing might grow you could save yourselves a lot of grief with a big OS, on the other hand the micro controllers coded in C are much easier to deal with for simple IO.

It's never easy ! (and if it was no one would pay you to do it)

Michael Kellett

@Paul,

The .net, for me, is because I already use about 6 programming languages daily. Adding one more has implications in terms of cost of the IDE, ramp up time in terms of using the IDE and the associated language requried, etc.

I have explained the choice of ARM above; in short it's because of what's in our product already. Also, from what I have seen, it's the "in fashion" proc. Having said that, since I am just starting out, I want a proc that I can scale up or down as needed.

I read your article (thanks for the link) and I agree that I don't want to go overboard on the proc if I don't need to. However, in my opinion, there are other factors than just what you are trying to physically do with the proc. For instance, if you create a design using a proc that totally fit your requirement but was in high demand and not easily available vs. one that was a bit more than you need and readlily available (at a small price difference), you may go with that, right?

Hi Ed,

As I said - you have to justify to yourself why you have selected a chips, tools etc you use. Yes you can ask about different devices and listen to people but in the end you have to make the choice not just follow bindly what you have done before, or others.

All best.

Hi ed,

In all fairness, most MCU's have the same caracteristics for general purpose applications.  Since you have chosen a processor, it is very important for you to define the device you plan to build and work out all of the processing threads, inputs and outputs.  You also need to assess your timelines for event responses.  At that point, you can look at your selected MCU to see if it meets those needs.  In some cases, you might have to use some extra hardware to make up for MCU limitations.

I have worked on many projects where the hardware was predefined and the software job was to make everything work.  This approach violates all reasonable system design processes, but you can still do the job.  It just makes it more risky to satisfy all of the requirements.

Your MCU selection is based upon your familiarity with the processor.  I can see your point in selecting an item you know well.  You will have to keep us posted on your progress so we can see how your decision plays out during your project.

Paul, I apologize for jumping in here, but I sensed the need to assess the issues and open up options for Ed.  While his approach is risky, it is not an unprecidented method used to develop prototypes for future production projects.

To all of you following these posts, I am prepared to start a series of blogs on the Systems Engineering Process if there is interest in doing so, but since the effort is non trivial, I need some assurance that my effort is desired.

Thanks

DAB

Systems Engineering Process -> Your effort is very much desired.

That's the heart of doing it right. Sometimes you do not start at either

end, but

in the middle and see what inputs and outputs are required.

Frank Senftle

/***********************/

Good morning,

I'm an electrical engineering student and currently working an a PIC32MX795F512L microcontroller project and I am having difficulties downloading the FreeRTOS on it using MPLAB X. I was wondering if you could maybe help me with some advice.

Thank you.

Hi DAB,

More than happy for people to add to this, thats the idea for people to give view points and help. People will have had experiance on things I have not etc. So its good.

Also I would just do the blogs. It takes time to get a folowing but I can say that any content generated is always welcome - and let me know when you do as I for one would be intrested.

Hi dragonball,

Unfortuantly I do not have any experiance with RTOS - but hopfully other here may be able to help.

Maybe you could start by explaining in more detail what issues you are getting.

Thanks

dragonball,

The free RTOS page offers a link to a Microchip Application Note on Integrating Microchip Libraries with a Real-Time Operating System.

If you would like to look at a different RTOS please look here.