title: PCI express flow control credits
body: <p>I am reading PCI express documentation and have a question connected with “TLP Flow control Credits”.</p>
  
  <p>This is what I understood: as PCI express does not have sideband signal e.g. IRDY, TRDT, RBF, is uses flow control credit model.  There are different type of TPs PH, PD, NPH, .. , and eash of them has their own credit.</p>
  
  <p>Is my understanding right?
  And I don’t clearly understand what are the next steps with these credits. Can someone explain please?</p>
  
  <p>Thanks</p>