How easy is it to implement an ascii serial port on OpenAt?



I have a client that has one of my embedded designs controlled via a wavecom modem over GSM. The embedded unit is controlled remotely via a uart interface and a dial-in, using hyperterminal on a PC as the control application; it also periodically reports its status over the uart interface using SMS to a mobile handset. The client now wants to evaluate GPRS since the deployment of the product may be growing.

Because of my lack of familiarity with networking software, what I can’t yet figure out from all the information that’s easily digestible, is which is going to be the cheapest development path (i.e. shortest time). If I read every piece of documentation going to figure all this out it would take a week of costs and the answer may be that Open AT is not it.

Do I implement a TCP/IP stack on my embedded unit and use PPP over the uart or do I develop apps for the OpenAT modem which just provide a serial ascii interface over the uart? I suspect it is trivial but I might have a lot of messing around to find out I’m wrong.

So how easy is it in OpenAT to provide a simple serial ascii output over the uart of say a ‘fasttrack supreme’? How much code do I have to create to provide the existing functionality that my client has, but using GPRS rather than a dial-in?

Eventually I’d like to port the embedded application on to the OpenAT modem and just provide the real world I/O interface as this would suit the client better, but that is too big a step to take at this stage.




If you do that, you not only have the learning curve of “networking software” in general, but you will also have to get right down into the detail of implementing (or, at least, porting) a TCP/IP stack.

Trying to “bolt-on” a TCP/IP stack to an existing embedded system can be far from trivial - especially for a networking novice…

There will, of course, be some learning-curve for Open-AT - but I suspect it’d be easier than learning and implemeting the whole thing from the ground up!

Not difficult at all - here’s one I prepared earlier:


You won’t, of course, be able to do that over GPRS - irrespective of whether or not you use Open-AT at the embedded end.

You will need to provide some sort of TCP/IP-based interface at the PC…

(Unless you’re planning on Telnet…)

BTW: how do you use Hyperterminal as a control application? Surely it’s purely an interface, so all the actual control is manual - by the user typing commands & viewing responses?


Thank you very much, awneil.

At this moment Hyperterminal is used to dial in and connect to the target. Once connected, ascii command
sequences (e.g. ‘pp:23,4,55>’ are used to control parameters or operation of the remote unit. Access security
is provided by a simple password and a check of the dialed-in number. The target responds with ascii strings,
mainly human-readable words; but not always.

This is primitive, but it’s all that is required and is nice and simple to maintain; the code space required is
minimal allowing low-end microcontrollers to be used. Also if necessary , the client would be able to deal with the
code. It suits their skill levels as much as mine. However that is going to change. They want/need GPRS.

You briefly mentioned Telnet. It sounds like that might be what I’m looking for. Along with the info from your
link, I have a lot of learning to do.


Steve Jag


Very easy.

You need to load the WIPsoft application which is supplied as standard. This then allows you to use and AT command set to operate and control GPRS over a serial port.


Steve Jag