1. On-Time Network On-chip
Dai Bui
Alessandro Pinto
Edward A. Lee
On-Time Network On-chip
Bounded Delay:
The interaction of packets of real-time flows makes real-time packets’ delays vary, however, packet delays of real-time flows never exceed estimated delay bounds and are much smaller than delays of best-effort packets, which are bout 5000 cycles.
The delay bound estimation seems to be conservative as there are some packets having delay equal to delay bounds.
Introduction:
Fixed Priority Packet Scheduler:
Step 1: Mature packets of real-time flows with the highest priority are selected to forwarded first.
Step 2 (optional): Any immature packets can be forwarded when there is no mature packets.
Game, multimedia, consumer and control applications today often demand high performance computing platforms that are able to deliver real-time services while satisfying tight power constraints.
Multi-core architectures supported by on-chip networks are merging as scalable solutions to fulfill these requirements. However, the increasing number of concurrent applications running on these platforms and the time-varying nature of the communication requirements give rise to communication delays and congestion that are difficult to predict.
We propose a simple and flexible instrumentation of the on-chip network that provides services to the application software for establishing end-to-end communication flows with timing guarantees.
Packet Multiplexing
Reservation of flows
Real-time flows have to commit their maximum packet rates and packet lengths in order to be set up. These information is necessary to compute delay bounds at each node for each real-time flow.
Admission control
Given the state of the NoC and a request to route a new real-time flow, establishes a suitable path for the route, if one exists, or rejects the request.
Delays and Buffers are Bounded:
The above scheduler guarantees a bounded delay and a bounded buffer for each real-time flow at each routers so no acknowledgement scheme is needed.
Heterogeneous Communication:
Bounded Buffer Sizes:
Buffer size for each real-time flows at each node is bounded as estimated.
Path Setup Protocol:
When a router wants to set up a new real-time flow, it sends a request to a master node, the master node will run some algorithms based on its knowledge about other real-time flows to find a suitable path. If a suitable path exists, it will send a setup command to routers on the path to make a reservation for the new flow.
Simulation:
Future Work:
Find a better routing algorithm for balancing load in network.
Integrate with PRET & PTIDES.
Implement in VHDL/Verilog.
Design tools for mapping applications to an on-time network on-chip.
Testing Example:
Three real-time flows are set up on a 5x5 mesh network so that they share some links with one another.
April 16, 2009
Center for Hybrid and Embedded Software Systems