CSE 291-a Interconnection Networks Lecture 12: Deadlock Avoidance (Cont’d) Router February 28, 2007 Prof. Chung-Kuan Cheng CSE Dept, UC San Diego Winter 2007 Transcribed by Yi Zhu

Topics  Deadlock avoidance Restricted physical route (lecture 10) Resource classes  Distance classes  Dateline (ring) Duato’s protocol  Router Architecture

Distance Classes  #classes >= diameter of network  At source, we inject packets into resource of class 0  At each hop, the packet of class i acquires a resource of class i+1  Use min routing

Dateline (Ring)  There are two classes  A dateline cuts the ring into a string  At source, we inject packets into resources of class 0  Packets remain in the same class, but jump to class 1 when crossing the dateline

Dateline (Ring)

Duato’s Protocol for Deadlock-Free Adaptive Algorithm  The underlying network is deadlock- free. The routing relation is R1: escape routing  Create new virtual resources and routing relation Rc  Rc -> R1 works as injection at the node.  R1 -> Rc not allowed

Router Architecture Physical channel state buffer

Virtual Channel State  Virtual channel state fields: 5-vector GROPC  G: Global state I (idle), R (routing) V (waiting for VC) A (active) C (waiting for credits)  R: Route, output port R for the packet  O: Output VC, output VC O of port R

Virtual Channel State (Cont’d)  P: Pointers, flit head and flit tail pointers into the input buffer  C: Credit count, #credits C for VC O of port R