void pl_Datime(TString sysinfo=""){
  TCanvas *can = (TCanvas *)gROOT->FindObjectAny("can");
  //cout <<" got can = "<<can<<endl;
  if(NULL == can) return;
  //can->Draw();
  can->cd();

/*
    https://root-forum.cern.ch/t/writing-text-on-foreground-on-a-canvas/17435/2
*/
  TPad *newpad=new TPad("newpad","a transparent pad",0,0,1,1);
  newpad->SetFillStyle(4000);
  newpad->Draw();
  newpad->cd();
/*
TPaveLabel *title = new TPaveLabel(0.1,0.94,0.9,0.98,"Drawing options for one dimensional histograms");
title->SetFillColor(16);
title->SetTextFont(52);
title->Draw();
*/
 TDatime *pTime=new TDatime();
  //cout << " add time stamp to canvas " <<pTime->GetDate() << ", "<<pTime->GetTime() <<endl;
  TPaveText *pt = new TPaveText(.90,.975,.99,.99,"blNDC");
  pt->SetBorderSize(0);
  pt->SetFillColor(0);
  pt->AddText(Form("%d,%d",pTime->GetDate(),pTime->GetTime()));
  pt->Draw();
  if(sysinfo!=""){
    cout << " add to canvas: sysinfo = " << sysinfo.Data() << endl; 
    TPaveText *st = new TPaveText(.96,.9,.995,.2,"blNDC");
    st->SetBorderSize(0);
    st->SetFillColor(0);
    TText *text = (TText *) st->AddText(Form("%s",sysinfo.Data()));
    text->SetTextAngle(-90);
    text->SetTextSize(0.016);
    text->SetTextColor(4);
    st->Draw();
  }
}