timeout error downloading a file wirelessly from an ftp server using AT commands

Projects Programming
1

HI,
I am using an arduino uno R3 and a GSM/GPRS shield (SIM900) to download files from an FTP server using the sim900 AT commands. The code and the responses to the code from the sim900 are given below. Everything seems to work except for actually getting the data from the server which is when i get the timeout error. The main problem is that i cant "see" the server responses to see what is causing the timeout error. The timeout error is indicated by +FTPGET=1,64 (64 = timeout) should be +FTPGET=1,1 every thing after the time out obviously fails.

Can anybody see any problems with how i am doing this and maybe suggest a better way (TCP/IP??).

Any help is much appreciated.

Cheers.

#include <SoftwareSerial.h>

SoftwareSerial sim900(7, 8);

int x;
char data[1024];

void setup(){
  Serial.begin(9600);    // UART baud rate
  sim900.begin(19200);
  Serial.println("Starting FTP Download...");
 
  for (int i=0;i< 5;i++){
    delay(2000);
  }
  
  //Serial.println("AT+CGSOCKCONT=1,\"IP\",\"myapn\"");
  //Serial.flush();
  
  //response();
}

void loop() {
  sim900.println("AT"); //check AT
  sim900Reply();
  sim900.println("AT+CSQ"); //check signal strength
  sim900Reply();
  sim900.println("AT+CGATT?");
  sim900Reply();
  sim900.println("AT+CSTT");
  sim900Reply();
  
  /*sim900.println("AT+CIICR");   
  //Serial.flush();
  sim900Reply();
  sim900.println("AT+CIFSR");   
  //Serial.flush();
  sim900Reply();*/
  
  sim900.println("AT+SAPBR=3,1,\"CONTYPE\",\"GPRS\"");
  sim900Reply();
  sim900.println("AT+SAPBR=3,1,\"APN\",\"internet\"");
  sim900Reply();
  sim900.println("AT+SAPBR=1,1");
  sim900Reply();
  sim900.println("AT+FTPCID=1");
  sim900Reply();
  sim900.println("AT+FTPMODE=1");
  sim900Reply();
  sim900.println("AT+FTPTYPE=\"A\"");
  sim900Reply();
  sim900.println("AT+FTPSERV=\"ftp.xxxx.xx.xx\"");            //write your FTP server domain
  sim900Reply();
  sim900.println("AT+FTPUN=\"user\"");
  sim900Reply();
  sim900.println("AT+FTPPW=\"pass\"");
  sim900Reply();
  sim900.println("AT+FTPGETNAME=\"test.log\"");
  sim900Reply();
  sim900.println("AT+FTPGETPATH=\"/file/path/\"");        //write the correct directory path. 
  sim900Reply();
  sim900.println("AT+FTPGET=1");                             //starts FTP session
  sim900Reply();
  sim900Reply2();
  sim900.println("AT+FTPGET=2,1024");                        // gets 1024 bytes of data
  sim900Reply();
}

void sim900Reply() {
  x=0;
  do{
    //Serial.println("in here");  //testing
    while(sim900.available()==0);
    data[x]=sim900.read();
    Serial.print(data[x]);
    x++;
  } while(!(data[x-1]=='K'&&data[x-2]=='O'));
}

void sim900Reply2() {
  x=0;
  do{
    while(sim900.available()==0);
    data[x]=sim900.read();
    Serial.print(data[x]);
    x++;
  } while(!(data[x]=='+'));
  do{
    while(sim900.available()==0);
    data[x]=sim900.read();
    Serial.print(data[x]);
    x++;
  } while(!(data[x]=='\n')||(data[x]=='\r'));
}

SIM900 reponses;

Starting FTP Download...
AT

OK
AT+CSQ

+CSQ: 23,0

OK
AT+CGATT?

+CGATT: 1

OK
AT+CSTT

OK
AT+SAPBR=3,1,"CONTYPE","GPRS"

OK
AT+SAPBR=3,1,"APN","internet"

OK
AT+SAPBR=1,1

OK
AT+FTPCID=1

OK
AT+FTPMODE=1

OK
AT+FTPTYPE="A"

OK
AT+FTPSERV="ftp.xxxx.xx.xx"

OK
AT+FTPUN="user"

OK
AT+FTPPW="pass"

OK
AT+FTPGETNAME="test.log"

OK
AT+FTPGETPATH="/file/path/"

OK
AT+FTPGET=1

OK

+FTPGET:1,64
AT+FTPGET=2,1024

+CME ERROR: operation not allowed
2 
void sim900Reply() {
  x=0;
  do{
    //Serial.println("in here");  //testing
    while(sim900.available()==0);
    data[x]=sim900.read();
    Serial.print(data[x]);
    x++;
  } while(!(data[x-1]=='K'&&data[x-2]=='O'));
}

This is crap. You almost certainly do not want a do/while loop here. A do/while statement will execute the body of the loop at least once, which is probably NOT what you want.

You set x to 0, but you do not reset data[ 0 ] or data[ 1 ]. Suppose that you receive an 'O'. You store that in the 0 position of data, increment x to 1, and then test the 0th position and the -1th position of the array. BAD!

Suppose that the AT command failed. The response will NOT be "OK", and your do/while loop will never end. Does that seem like a good idea?