GPRS unable to compare "OK" commands.

[Rohi231]

Hello . I am interfacing GPRS with add semiconductor. I am unable to compare the "OK" commands. When i put
len=strnlen(rec);

what will be the length of len of "OK" commands.

 

[not-a-moderator]

The responce from most (not all) GSM modules would be:

"OK<cr><lf>"

Check in its data manual for the formatting of its AT command responses.

Therefore if you are using the C/C++ library function strlen() you would get a length of 4.

https://www.cplusplus.com/reference/clibrary/cstring/strlen/

 

[Rohi231]

Thank you moderator. I need the solution for this string. When
while(strcmp (strx,str1) != 0) ;



if condition gets true what will happen now. I am unable to trigger it out. plz help me.

 

[not-a-moderator]

Thank you moderator. I need the solution for this string. When
while(strcmp (strx,str1) != 0) ;



if condition gets true what will happen now. I am unable to trigger it out. plz help me.

If what you are trying to do is to wait for the module to send you the "OK<cr><lf>" response a possible implementation could be:

//issue command to gsm module
-- blah
-- blah

//wait for OK response
str1 = "OK<cr><lf>";
strx = "";
fail = 0;
while((strcmp (strx,str1) != 0) || fail = 0);
{
strx = gets(Usart_Rx_Buffer);
if(strx = Some_other_predefined_error_message_from_module)
fail = 1;
}

//proceed to give gsm module its next task


Refresh your mind when working with strings. Also have a look at The break; statement
https://www.cplusplus.com/doc/tutorial /control/

 

[FvM]

An important point when writing AT command interfaces is not to rely on assumptions about a specific response format. The first step will be to strip off delimiters and leading spaces.

I don't know what gets() is supposed to do, but I would expect that <CR><LF> is removed from the response string. In this case, the compare would fail.