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Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 ECE 697F Reconfigurable Computing Lecture 6 Mapping to Embedded Memory and PLAs.

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Presentation on theme: "Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 ECE 697F Reconfigurable Computing Lecture 6 Mapping to Embedded Memory and PLAs."— Presentation transcript:

1 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 ECE 697F Reconfigurable Computing Lecture 6 Mapping to Embedded Memory and PLAs

2 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 Outline °Overview Targeted to existing hybrid PLA/LUT FPGAs Area and timing-constrained mapping °HybridMap Graph-based approach Post-map product term estimation °Results Comparisons with existing approaches Mapping to Apex20KE °Acknowledgement: Srini Krishnamoorthy

3 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 Hybrid FPGAs with LUTs and PLAs °LUTs Dense logic, small number of inputs Special circuitry for arithmetic logic °PLAs For wide fanin, low logic density structures Control-logic (e.g. Finite State Machines) °Device containing both resources Move maximum logic to PLAs Implement remaining logic in LUTs Inputs Reset Output

4 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 Hybrid FPGAs °Resources LUT blocks and Pterm macrocells °Objective Minimize 4-LUT area subject to design performance constraints Potential use: smaller devices °Key factor Efficient partitioning of design components

5 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 Hybrid FPGA (Similar to APEX20KE Megalab) Global Interconnect LE 1 LE 2 LE 3 LE 4 LE 5 LE 6 LE 7 LE 8 LE 1 LE 2 LE 3 LE 4 LE 5 LE 6 LE 7 LE 8 PLA LUTs Local Interconnects

6 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 HybridMap Flow SIS Tech. Independent Optimization Node Partitioning Design Entry LUT Identification Subgraph Generation Pterm Estimation Area Estimation Subgraph Merging Pterm Estimation Area Estimation LUT Mapping PLA Mapping Place and Route PLA Subgraphs LUT Partition Mapped Design Vendor-Specific CAD

7 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 LUT Identification I1 I2 I3 I4 I5 I6 I7 O1 O2 O3  Design initially reduced to 2-input gates  Topological traversal starting from primary inputs  Input count to any LUT cluster is less than K  A node always belongs to the cluster that minimizes delay  LUT clusters are preliminary  Used to estimate LUT count  Similar to DAG-map (Lawler’s alg) LUT Cluster

8 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 Subgraph Generation Maximum Fanout Free Cone (MFFC) Maximum Fanout Free Subgraph (MFFS) - All edges except output edge(s) stay within the cone O O1 O2

9 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 Subgraph Generation V Search Root-set determination (Forward BFS) Condition: Nodes at each level <= O pla  Extract a multi-input, multi-output subgraph  Root set determination  Identify subgraph outputs  Forward traversal  Subgraph identification  Identify the subgraph inputs  Backward traversal

10 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 Subgraph Identification V I3 I2I1I0 Search Subgraph determination (Backward BFS) O1 O2 O3 O4 O5 Condition: Inputs <= I pla, Backward breadth first search until input constraint met

11 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 Reconvergent Paths  Hill-climbing approach  Start basic subgraph search algorithm from v  If nodes encountered > O pla  Neglect PLA output constraint  Continue search  When nodes encountered < O pla  Revert back to basic search algorithm V I1 I2 I3 I4 O1 O2 basic hill climbing basic Search

12 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 Subgraph Pruning  Hill-climbing subgraph may violate PLA I/O constraints  Need to prune  Pruning steps  Collapse subgraph to two- level form  Remove outputs requiring least inputs  Outputs requiring K inputs (single LUT removal)  Minimal multi-LUT removal PLA

13 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 Subgraph Combining Smaller subgraphs can be packed onto a single PLA Combine based on cost function -LUT savings due to merging -Input sharing -Pterm count Choose 2 subgraphs for merging based on combined feasibility in terms of PLA inputs, outputs and Pterms -Invoke Pterm estimator SG 1 SG 2

14 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 Results: Effect of Initial Graph Node Size Resources: 4-LUTs, 32 Input 16 Output 32 Pterm Macrocells  2-Input case  Identify PLA Partitions  Map rest to LUTs using Flowmap  4-Input case  Map initially to LUTs  Extract PLA Partitions  13 MCNC benchmarks (8939 LUTs initially) Total LUT Savings 2357 1367 364 2358 1255 316 R=10 R=5 R=10 R=5 R=1 R Number of PLAs 2-input nodes 4-input nodes

15 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 Altera software: Quartus v2000.02 Timing Constrained Case : 8% LUT Reduction Unconstrained Case : 14% LUT Reduction Mapping to APEX20KE-1

16 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 Summary Hybrid FPGAs: A challenging problem Subgraph based approach to technology mapping Pterm based macrocells, Pterm estimation Unconstrained and timing constrained mapping -Delay and area estimation an important part of the mapping process Results -Pterm estimation improves LUT coverage by about 12% - Apex20KE devices –Unconstrained : 14% 4-LUT savings –Timing constrained : 8% 4-LUT savings

17 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 Notes for Transcription Assignment °Focus on one main point °Write an outline °Check English and spelling

18 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 Transcription Introduction Lecture summary Summary of papers Contrast of papers Conclusion References

19 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 Overview Paper should be focused on a primary goal -May not be obvious until after reading -What will the reader take away from this work -Is there a common theme Introduction -Should summarize the entire paper. -Each paragraph presents a main idea -Ideas should be detailed but sufficiently high-level. -Results paragraph should present a result to support the theme.

20 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 Tackling the Body Lecture summary -Brief review of the lecture -Focus on main point -Should flow seamlessly into/with papers -I can make powerpoint available Summary of papers -Discussion of main approaches -Important new techniques -Main point made by author -Main result/results

21 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 Contrasting the Papers Pick categories for comparison -Should be three to four Each section should contrast a different category. -Try to focus on specific details of each paper Consider using a table to supplement text. -Helps clarify detailed comparison Focus on comparison rather than restating the details

22 Lecture 6: Mapping to Embedded Memory and PLAs September 27, 2004 Other Tips Have a friend review your work. Try to keep sentences focused -Subject – verb – description Avoid using first person. Write a detailed outline before you write any text. Give yourself plenty of time You should have at least four or five references.

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