Wire Planning with consideration of Electromigration and Interference Avoidance in Analog Circuits 演講者 : 黃信雄 龍華科技大學 電子工程系

Outline  Introduction  Preliminary  Algorithms  Experimental Result  Conclusion and Future Work

Outline  Introduction  Preliminary  Algorithms  Experimental Result  Conclusion and Future Work

Introduction(1)  Electromigration (abbreviated as EM) due to insufficient wire width can cause the premature failure of a circuit. 1000mA EM reduce the product circuit life open short We must improve reliability [11] J. Lienig and G. Jerke, “Current-Driven Wire Planning for Electrimigration Avoidance in Analog Circuits,” in Proc of Asia and South Pacific Design Automation Conference, pp , These pictures are published in [11]

Introduction(2) 1. Wire planning 2. Detail routing Electromigration reduce circuit life Total wiring area :840 Avoid electromigration to increase circuit life Total wiring area :1830 Electromigration aware analog design flow Avoid electromigration to increase circuit life Total wiring area :2520

Introduction (3)  Previous Works Minimize total wiring area without obstacle  Greedy-based approach [11] [19] Minimize total wiring area with obstacle  Greedy-based approach [1][12] Minimize total wiring area without interference consideration  Greedy-based approach [1] [11] [19][12] [11] J. Lienig and G. Jerke, “Current-Driven Wire Planning for Electrimigration Avoidance in Analog Circuits,” in Proc of Asia and South Pacific Design Automation Conference, pp , [19] J.T. Yan Z.W. Chen and D.H. Hu, “Electromigration-Aware Rectilinear Steiner Tree Construction for Analog Circuits,” in Proc. of 18-th VLSI Design and CAD Symposium, CD-ROM, [1]T. Adler and E. Barke, “Single Step Current Driven Routing of Multiterminal Signal Nets for Analog Applications,” in Proc. of Design, Automation and Test in Europe, pp , [12]J. Lienig, G. Jerke, T. Adler, “Electromigration Avoidance in Analog Circuits: Two Methodologies for Current- Driven Routing,” in Proc. of IEEE International Symposium on VLSI Design, pp , 2002.

Introduction (4)  Contributions First, to avoid the electormigration of the circuit, the greedy-based approach, which formulates the problem into the graph model, is used to automatically determine the feasible connections between sources and targets with the proper wire width. Second, to avoid the interference between the obstacle and wires, the space reservation [5][11] is utilized for all obstacles. Third, the proposed method efficiently determines the routing path to reduce the total wiring area.

Outline  Introduction  Preliminary Terminology Problem Formulation  Algorithms  Experimental Result  Conclusion and Future Work

Terminology(1) - Adjust Line  If we can not find the feasible path by two pattern routing, the shorter line is applied.

Terminology(1) - Adjust Line  The length from the source and target. is computed as follows [9],  where and are the additional wire lengths of the upper-L and low-L routing paths from source to target with the obstacle k,

Terminology(2) - Wiring area  To avoid the EM, the wire width is proportional to current value. We have the formula, where and are the wire width and current value for source i and target j, respectively.  Therefore, the wiring area is computed as, where is the constant. 

Terminology(3) - Interference  Predefined IP is regards as the obstacles  To avoid the interference  Space reserve the dead-space for obstacles

Problem Formulation  Given: A set of sources S = {s 1, s 2,…, s n } with their corresponding root-mean-square (RMS) current values {O 1, O 2,…, O n }. A set of targets T = {t 1, t 2,…, t m } with their corresponding root-mean-square (RMS) current values {I 1, I 2,…, I m }. A set of rectangular obstacles B = { b 1, b 2,…, b k }.  Objective: To construct an wire planning result with minimal wiring area by consideration of the obstacles and electromigration (abbreviated as EM).

Outline  Introduction  Preliminary  Algorithms ILP-based Algorithm Graph-based Algorithm  Experimental Result  Conclusion and Future Work

ILP-based Algorithm(1) Input: (1) A set of sources and a set of targets (2) Their equivalent RMS current values (3) A set of obstacles Output: A EM-aware wire planning with minimal area Method: Step 1. Perform space reservation for obstacle; Step 2. Calculate the Length for Source-Target pairs; Step 3. Determine the Topology by ILP Formulations ; Step 4. Transform the M-architecture Results;

Perform space reservation for obstacle  The user-defined space  Construct a better wire planning with less interference

Initial circuits

Construct the bipartite graph

Calculate all source-to-target wirelengths  The wirelength of each source-target is computed  The length is integrated into the ILP formulations. ILP formulations

Determine the topology with proper wire width  Determine the topology with proper wire width by ILP formulations. Subject to Kirchoff’s current law Total wiring Area Source driving current constraint Target sinking current constraint Wire width

Determine the topology with proper wire width min=wiring_area; wiring_area=c(1,4)*d(1,4)+c(1,5)*d(1,5)+c(1,6)*d(1,6)+c(1,7)*d(1,7)+ c(1,8)*d(1,8)+C(1,9)*d(1,9)+c(1,10)*d(1,10)+c(2,4)*d(2,4)+c(2,5)*d(2,5)+ c(2,6)*d(2,6)+c(2,7)*d(2,7)+c(2,8)*d(2,8)+c(2,9)*d(2,9)+c(2,10)*d(2,10)+ c(3,4)*d(3,4)+c(3,5)*d(3,5)+c(3,6)*d(3,6)+c(3,7)*d(3,7)+c(3,8)*d(3,8)+ c(3,9)*d(3,9)+C(3,10)*d(3,10); d(1,4)=18; d(1,4)=2070; d(1,5)=10850; d(1,6)=15190; d(1,7)=14570; d(1,8)=14190; d(1,9)=10200; d(1,10)=9330; d(2,4)=8850; d(2,5)=8270; d(2,6)=5950; d(2,7)=5450; d(2,8)=8850; d(2,9)=12780; d(2,10)=10290; d(3,4)=5030; d(3,5)=5430; d(3,6)=10390; d(3,7)=9770; d(3,8)=9070; d(3,9)=5700; c(1,4)+c(1,5)+c(1,6)+c(1,7)+c(1,8)+c(1,9)+c(1,10)=14; c(2,4)+c(2,5)+c(2,6)+c(2,7)+c(2,8)+c(2,9)+c(2,10)=32; c(3,4)+c(3,5)+c(3,6)+c(3,7)+c(3,8)+c(3,9)+c(3,10)=43; c(1,4)+c(2,4)+c(3,4)=10; c(1,5)+c(2,5)+c(3,5)=10; c(1,6)+c(2,6)+c(3,6)=9; c(1,7)+c(2,7)+c(3,7)=14; c(1,8)+c(2,8)+c(3,8)=16; c(1,9)+c(2,9)+c(3,9)=13; c(1,10)+c(2,10)+c(3,10)=17 ; c(1,3) = 0; d(1,3)= 250 c(1,4) = 0; d(1,4)=150 c(1,5) = 3; d(1,5)= 100 c(1,6) = 2 ; d(1,6)= 200 c(2,3) = 2; d(2,3)= 180; c(2,4) = 3; d(2,4)= 50; c(2,5) = 0; d(2,5)=200; c(2,6) = 1; d(2,6)= 200; ILP solver ILP formulations Result Wiring area wirelenth Source driving current constraint Target sinking current constraint

Determine the topology with proper wire width  After solving the ILP formulations, the connection is not exist if the current capacity is equal to zero. Result c(1,3) = 0; d(1,3)= 250 c(1,4) = 0; d(1,4)=150 c(1,5) = 3; d(1,5)= 100 c(1,6) = 2 ; d(1,6)= 200 c(2,3) = 2; d(2,3)= 180; c(2,4) = 3; d(2,4)= 150; c(2,5) = 0; d(2,5)=200; c(2,6) = 1; d(2,6)= 200;

Final EM-Oriented results  Wiring area is 1710

Outline  Introduction  Preliminary  Algorithms ILP-based Algorithm Graph-based Algorithm  Experimental Result  Conclusion and Future Work

Algorithm Input: (1) A set of sources and a set of targets (2) Their equivalent RMS current values (3) A set of obstacles Output: A EM-aware wire planning with minimal area Method: Step 1. Perform space reservation for obstacle; Step 2. Construct the bipartite graph; Step 3. Sort the weights of all edges; Step 4. Update weights of the relative edges; Step 5. Terminates until sources current are zero; Step 6. Adjust the invalid edges Step 7. Transform virtual obstacle into original one

Perform space reservation for obstacle  The user-defined space  Construct a better wire planning with less interference

Initial circuits

Construct the bipartite graph

 To minimize total wiring area, the weights of all edges in the complete bipartite graph are assigned by the formula, where is the Manhattan distance for source i and target j. is a user-defined constant.

Construct the bipartite graph

Sort the weights of all edges  The edge with smallest weight is first selected. 100(s1  t6) The other weights are 150,150,150,200,200,200

Remove the edge – iteration 1  The wire is built.

Update weights of the relative edges – iteration 1  The current of source and target are updated.

Update weights of the relative edges- iteration 1  The selected edge is removed.

Remove the edge – iteration 2  The edge with small weight is selected.

Remove the edge – iteration 2  The wire is built.

Remove the edge – iteration 2  The current of source and target are updated.

Update weights of the relative edges – iteration 2  The selected edge is removed.

Terminates until sources current are zero  The similar method is performed until the current of all sources have been assigned

Adjust the invalid edges  The invalid edge is adjusted by the push_line algorithm mentioned before. EM-oriented (long lifetime) Wiring are = 1830

Transform virtual obstacle into original one  The invalid edge is adjusted by the push_line algorithm mentioned before. EM-oriented (long lifetime) Wiring are = 1830 Less interference

Comparison of graph and ILP-based methods Wiring area =1830 ILP-based method (Effective)Graph-based method (Efficient) Wiring area = 1710

Outline  Introduction  Problem Formulation  Algorithms  Experimental Result  Conclusion and Future Work

Outline  Introduction  Preliminary  Algorithms  Experimental Result  Conclusion and Future Work

Experimental Result(cont’d)  Platform NameSpecification Hardware IBM Personal Computer Pentium (R) D – 3GHz with 2GB RAM OS Microsoft WindowsXP LanguageC++ languageVisual C ILP SolverLingo 11

Experimental Result (cont’d) CircuitNo. of obstacle R ob (%) No. of source No. of target r r r r r r [7]H.H. Huang, S.P. Chang, Y.C. Lin and T.M. Hsieh, “Timing-Driven X-Architecture Router among Rectangular Obstacles,” in Proc. of IEEE International Symposium on Circuits and Systems, pp , 2008.

Experimental Result (cont’d)  Comparison of the wiring area of graph-based and ILP-based method, the additional wiring area is reduced by 13.24%.  The ILP-based method works efficiently.

Outline  Introduction  Problem Formulation  Algorithms  Experimental Result  Conclusion and Future Work

Conclusions and future work  First, the proposed ILP formulations determines the wire connections with the proper wire width by RMS current values of sources and targets. Our ILP-based method optimize wiring area without obstacles.  Second, our method integrates the electromigration with obstacle for analog circuits to minimize the wiring area.  Third, the space reservation technique is used to avoid the interference between the wires and obstacles.  Compared to the results of greedy graph-based method, the proposed ILP-based method improved 13.24% wiring area on average.

Future work  The concept of signal integrity is considered to reduce the percentage of transformed edges[11].  How to obtain the better X-architecture results? (a) signal loss (b) signal integrity [11] J. Lienig, “Introduction to Electromigration-Aware Physical Design,” in Proc. of ACM International Symposium on Physical Design, pp.39-46, 2006.

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