I am trying to send data through GPRS via SIM300 modem. The logic of my program should be. 1) it should send the data till it receives "dieman" from the server. 2) the modem is such that after every command there is a reply. 3) all the communication takes place serially.
Firstly the GPRS commands as tried in hyperterminal
AT OK AT+CGATT=1 OK AT+CGDCONT=1,"IP","airtelgprs.com" OK AT+CSTT="airtelgprs.com","","" OK AT+CIICR OK AT+CIFSR 212.22.22.22 //EG OF AN IP ADDRESS AT+CIPSTART="TCP",""80"">http://www.google.com","80" OK CONNECT OK AT+CIPSEND >THIS IS THE DATA I WANNA SEND // YOU CAN SEND THE DATA VIA GPRS NOW [CTRL+Z] SEND OK
this is what i want to implement in C in 8052. here OK are the response from the modem.
now i implemented the C version but my code is very inefficient. I could have ignored the response from the modem by simply inserting delays but i want my code such that if the reply from the modem is not "OK" it should transmit the command again.
No, that would be a very bad idea indeed!
See my comment on "Arbitrary delays" in this thread: http://www.keil.com/forum/18684/
"i want my code such that if the reply from the modem is not "OK" it should transmit the command again"
That isn't a very good idea, either!
You should really make some attempt to determine the reason for the failure and, from that, determine what recovery action is appropriate.
As also mentioned in the above-mentioned thread, look-up AT+CMEE in your AT Commands manual...
OK, if i use the above code with improved quality of names assigned to variables is the code fine. And for generating a delay if i use TIMER in 8051. then is the problem solved.
is my logic for checking whether OK is received is correct?
No.
Walk through it by hand - with pencil and paper.
Or use the simulator.
The first usage might work - but what about the 2nd and subsequent...?
As Per said, what about echo from the modem?
Again, you are using arbitrary delays to guess when the response is complete...
See: http://www.keil.com/forum/18568/
See: http://www.keil.com/forum/16641/
On WikiBooks:
Serial Programming/Modems and AT Commands en.wikibooks.org/.../Modems_and_AT_Commands
In particular:
"People unfamiliar with the theory and practice of state machines often try to circumvent the issue by "tough coding". Which means, they throw more and more code onto the problem (wrapped in a heap of if/the/else/otherwise/maybe/... statements), until things seem to work - sort of. If they are lucky they have implicitly managed to create a state machine which works. If they are unlucky, they end up with a partial state machine, which breaks down should something unusual happen in the communication. This usually comes with the problem that the software was not designed to recover if things break down. So such software tends to hang or crash."
You code falls into that category.
And I heartily support their recommended solution:
"It is much more efficient to first spend a few hours to to learn the basics of simple state machines, and then spending a few more hours to describe the communication with the modem as a state machine. The result of this planning serves as a nice template for implementing the DTE software." (my emphasis)
On one thing I disagree, though: "a few hours" is very optimistic: as a novice, you should look to dedicate significantly longer to master State Machines - also known as Finite State Machines, or FSM for short.
Direct link to the bit about State Machines:
en.wikibooks.org/.../Modems_and_AT_Commands
Thank you,
I will go through the links and would let u know if other doubts happen to occur.
Thnx once again