#18 Crash if USB->Serial adaptor is removed

[Anonymous]

If you're using an USB to serial adaptor and unplug the
USB cable while the COM port is open your program will
crash seriously.

[odissey1]

Logged In: YES
user_id=1659492
Originator: NO

Hi,

Having the same problem I came to a solution so far as shown below.

Corrections in CPort.pas v.3.10 to work with USB-RS232 correctly (//BMT-my changes)

in:

function TCustomComPort.Signals: TComSignals;
var Status: DWORD;
begin

{//replace this->
if not GetCommModemStatus(FHandle, Status) then
raise EComPort.Create(CError_ModemStatFailed, GetLastError);}

//to this->
if not GetCommModemStatus(FHandle, Status) then
DoError([ceBreak]);//fire ceBreak instead

...

end;

Comment: When USB is unplugged, ComPort1.OnError event will be fired, you can process disconnect there (change some buttons state or stop your transmit/receive operations). Also in OnError event, do not use ComPort1.Close, or ComPort1.Port='', because there is nothing to close anyway. Just ignore that.

in AbortAllAsync just comment all lines - I don't see any problems so far with that:

procedure TCustomComPort.AbortAllAsync;
begin
//BMT if not PurgeComm(FHandle, PURGE_TXABORT or PURGE_RXABORT) then
//BMT raise EComPort.Create(CError_PurgeFailed, GetLastError);
end;

Comment: PurgeComm causes a problem ('Purge Coom funcion failed, (Win Err code:5)') when hot unplug of USB-RS232 devices. Just comment all lines to ignore everything in AbortAllAsync. I don't see any problem yet. We don't need to Purge Comm port which does not exist anyway.

Regards,
dissey1

[Nobody/Anonymous]

Logged In: NO

I use bcb5 and had this problem, it seem largely related to the strings being returned when the exception handler was fired.

// create exception with windows error code
constructor EComPort.Create(ACode: Integer; AWinCode: Integer);
begin
FWinCode := AWinCode;
FCode := ACode;
//inherited CreateFmt(ComErrorMessages[ACode] + WideString(' (win error code: %d)'), [AWinCode]);
end;

I commented out the call to inherited CreateFmt(ComErrorMessages[ACode] + WideString(' (win error code: %d)'), [AWinCode]);
and the crashes/ blue screens went away.

Not a deterministic solution but it seems to be robusts, I can pull the usb in and out and no crashes any more.