SpaceWire Hot Modules International SpaceWire Conference 2007 17-19 September 2007 SpaceWire Hot Modules Asaf Baron, Isask'har Walter, Israel Cidon, Ran Ginosar, Isaac Keslassy EE Department, Technion, Haifa, Israel Ofer Lapid Israel Ministry of Defense

An end unit may receive heavy traffic from several sources Hot Module An end unit may receive heavy traffic from several sources The heavy load congests the network Blocks other (light) traffic Enhancing the network will not help Problem is with the end unit, not the network Such unit is a HOT MODULE The heavy load congests the network as long worms spread across it

Example network D1 D2 D3 D4 D5 DHS S5 S4 S3 S2 S1 Storage 29 25 26 27 28 22 23 21 24 18 19 17 20 14 15 13 16 10 11 9 12 6 7 5 8 2 3 1 4 Should say that parts and traffic requirements were taken from the paper “Benchmarking SpaceWire Networks” S5 S4 S3 S2 S1 Storage

Two main problems System Performance Source Fairness Router 5 Router 4 DHS Router 5 Router 4 Router 3 Router 2 Router 1 Reaction Wheel Storage S5 S4 S3 S2 S1

Solution #1 Use Packet Level Priority (PLP) Assign low priority to packets that are traveling to the Hot Module Improves System Performance But does not solve Fairness DHS Router 5 Router 4 Router 3 Router 2 Router 1 Reaction Wheel Need to mention that there is a separate Round Robin arbitration for each priority Storage S5 S4 S3 S2 S1

Solution #2 Problem: traffic sent to Storage (Hot Module), congesting the network Introduce Credits: Before sending to Hot Module, ask for credit No need to modify routers

Credits Improve Performance & Fairness DHS Router 5 Reaction Wheel Router 4 Router 3 Router 2 Router 1 Storage S5 S4 S3 S2 S1 Improves System Performance Solves Fairness

Simulations Use our new SpW simulator and benchmark No more than 2 Sensors have credits at a time

Traffic to Hot Module PLP CREDITS PLP + CREDITS Sensor 5 Sensor 1 Equally getting heart Average ETE delay to Hot Module remains more or less the same

Traffic to DHS (non-Hot-Module) PLP CREDITS PLP + CREDITS A curve here represents traffic that needs to traverse over X hops. For example …

Conclusions: Hot Modules incur two effects Source Fairness Solved using Credits Performance Improved using PLP and Credits Using PLP + Credits yields the best results