P1          P2           P1          P2            P1       P2                P1        P2
     Flash1     flash1     Flash2    flash2    Flash3     flash3     flash4     flash4
        l             l             l            l              l            l              l            l
          flash1                   flash2                     flash3                   flash4   
             l                            l                            l                           l
                         flash2                                                 flash3
                            l                                                         l 
                                                          
                                                       flash2