B4J Question how to continue process

public Sub test(interval As Int) as int
   dim retn as int
   Dim now As Long=DateTime.Now
   Do While True
      if IsItRespone(data,20) then
         retn = 0 ' OK, I got a packet from RS-232
         exit
      else
        If (DateTime.Now-now)>interval Then
          retn = -1 ' NG, I haven't got a packet from RS-232
          exit
        End If
      End If
   
   Loop
   return retn
End Sub