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How to parse AT command

Posted on 2011-09-27
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Last Modified: 2012-05-12
I'm starting a project that create a virtual modem. The modem receive an AT command and response it follow the command. But I don't know (don't have the idea) to parse the AT command to cover all of the cases.Anyone have the source code or document relate how to parse AT command using C language please suggest me. Thanks so much.
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Question by:nnemo33
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Hugh McCurdy earned 500 total points
ID: 36712837
Do you have the AT command set?  If not, I found this -- http://en.wikipedia.org/wiki/Hayes_command_set

I don't have code for you but I have a plan.  I would treat the commands as a tree an implement using mostly switch statements.  I would also use if statements near the bottom as applicable.  Here's an example of the top.  This is assuming that I've already determined the first two characters were indeed AT.

pCh is a pointer to the 3rd character at this point in execution.

switch ( *pCh )
{
    case 'A':
        Third_A ( pCh + 1 );
        break;

    case 'D':
        Dial ( pCh + 1 );
        break;

......

}


function Third_A ( char *pCh )
{
    switch ( *pCh )
    {
        case '0':
        case '\0':
            AnswerCall();
            break;

        case '/':
            RepeatLastCommand();   // Somehow you'd have to know what this is.  I have ideas if you don't.
            break;

        default:
            ErrorHandlerForUnknownCommand();
            return -1;
    }

    return 0;
}

Open in new window



As I think about the problems, it occurs to me that C++ might be a better choice.  But that's up to you.
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Expert Comment

by:ssnkumar
ID: 36889949
Have you looked at mgetty and vgetty - that is an opensource software related to modem, fax, etc.
You can look at it at: http://mgetty.greenie.net/
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LVL 8

Expert Comment

by:ssnkumar
ID: 36889961
Here is a page regarding "Controlling your Modem with AT Commands": http://www.zoltrix.com/support_html/modem/usemodem.htm

You can see the implementation of "Linux Generic Soft Modem" at: http://bellard.org/linmodem.html
The above software has a AT command parser.

And also, you can refer the following link to look at "Simple Hayes AT Command Parser": http://embeddedfreak.wordpress.com/2008/11/03/simple-hayes-at-command-parser/
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