modem call in c++ - c++

Question

I'm trying to make a modem call in one end, and in the other end the program answers the call. It doesn't seem to detect the carrier. Am I doing anything wrong? Am I missing something?
int main(int argc, char** argv)
{
ParseArgs(argc,argv);
SerialPort* port = SerialPort::New();
if(!port)
Error(ErrorNoMemory,"Can't create port");
int error = port->Open(PortNum, SendFlag);
if(error)
Error(error,"Can't open port");
error = port->Initialise(PortBaud);
if(error)
Error(error,"Can't initialise port");
if(ReceiveFlag)
{
port->Listen();
Receive(port); //after the call is stablished I send a file
}
else
{
port->Dial(PhoneNumber);
Send(port);
}
port->Close();
delete port;
return 0;
}
The part of opening the port:
int Open(unsigned port, bool SendFlag)
{
// make name for port...
char name[] = "\\\\.\\com???.???";
char* nameNumber = name+sizeof(name)-8;
char* nameEnd = nameNumber;
if(port>999){
return ErrorInvalidPort;
}
if(port>99)
{
*nameEnd++ = '0'+port/100;
port %= 100;
}
if(port>9)
{
*nameEnd++ = '0'+port/10;
port %= 10;
}
*nameEnd++ = '0'+port;
*nameEnd = 0;
// open port...
hSerial = CreateFile(name, GENERIC_READ|GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, NULL);
if(hSerial==INVALID_HANDLE_VALUE)
{
switch(GetLastError())
{
case ERROR_FILE_NOT_FOUND:
return ErrorInvalidPort;
case ERROR_ACCESS_DENIED:
return ErrorPortInUse;
default:
return Error();
}
}
SetupComm( hSerial, 1024, 1024 );
if (!SendFlag)
{
if (!SetCommMask(hSerial, EV_RING |EV_RLSD))
// Error setting communications mask
printf("error mascara");
}
else
{
if (!SetCommMask(hSerial, EV_RLSD))
{
// Error setting communications mask
printf("error mascara");
}
}
return 0;
}
The initialise part:
int Initialise(unsigned baud)
{
// flush port...
if(!FlushFileBuffers(hSerial))
return Error();
if(!PurgeComm(hSerial, PURGE_TXABORT|PURGE_RXABORT|PURGE_TXCLEAR|PURGE_RXCLEAR))
return Error();
// configure port...
DCB dcb ;
if(!GetCommState(hSerial, &dcb))
return Error();
dcb.BaudRate = CBR_115200;
dcb.ByteSize = 8;
dcb.StopBits = ONESTOPBIT;
dcb.Parity = NOPARITY;
if(!SetCommState(hSerial, &dcb))
{
if(GetLastError()==ERROR_INVALID_PARAMETER)
return ErrorInvalidSettings;
return Error();
}
// set timeouts to zero so read/writes return immediately...
COMMTIMEOUTS timeouts = {0};
timeouts.ReadIntervalTimeout = MAXDWORD;
timeouts.ReadTotalTimeoutConstant = 0;
timeouts.ReadTotalTimeoutMultiplier = 0;
timeouts.WriteTotalTimeoutConstant = 0;
timeouts.WriteTotalTimeoutMultiplier= 0;
if(!SetCommTimeouts(hSerial, &timeouts))
return Error();
// flush port again...
if(!PurgeComm(hSerial, PURGE_TXABORT|PURGE_RXABORT|PURGE_TXCLEAR|PURGE_RXCLEAR))
return Error();
return 0;
}
The dial part:
int Dial(char *telefono)
{
unsigned long int n = 0;
DWORD dwCommEvent;
DWORD bytes;
DWORD dwRead;
char cadena[15];
char chRead;
sprintf(cadena, "ATDT%s\r", telefono);
if (!WriteFile( hSerial, "ATH1\r", strlen("ATH1\r"), (&(n)), 0 ))
{
printf("error");
}
FlushFileBuffers( hSerial );
Sleep(1000);
if (!WriteFile( hSerial, cadena, strlen(cadena), (&(n)), 0))
{
printf("error");
}
FlushFileBuffers( hSerial );
Sleep(10000);
printf("Marcamos");
do
{
printf("Espero eventos");
if(WaitCommEvent(hSerial, &dwCommEvent, NULL))
{
if(dwCommEvent & EV_RLSD)
{
printf("rlsd");
break;
}
else
{
printf("otro");
}
}
printf("fin del bucle");
} while(true);
return 0;
}
The listening part:
int Listen()
{
DWORD dwCommEvent;
unsigned long int n = 0;
do
{
printf("ESpero eventos");
if(WaitCommEvent(hSerial, &dwCommEvent, NULL))
{
if(dwCommEvent & EV_RING)
{
printf("RING");
if (!WriteFile( hSerial, "ATA\r", strlen("ATA\r"), (&(n)), 0 ))
{
printf("error");
}
FlushFileBuffers( hSerial );
break;
}
else if (dwCommEvent & EV_RLSD )
{
break;
}
}
printf("fin del bucle");
} while(true);
return 0;
}

Answer 1

You might have an easier time of it using Microsoft's Telephony API (TAPI) rather than trying to talk to the modem directly.

Answer 2

You may want to try issuing an ATS0=1 on the receiving side and let the modem autoanswer (substitute the number of rings you want instead of 1 if you wish).
You may discover that smart modems don't always pass through the ring (EV_RING) signal.
EDIT: Don't forget to 'ATS0=0' when you don't want the modem to auto-answer any more.

Answer 3

Maybe you need to apply the A0 and / or S0=1 Hayes command on the answering side.