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ASIC System Design Challenges: Floorplanning & Power Planning in today’s large chips Amin Farmahini Farahani Instructor: Prof. S. Mehdi Fakhraie ASIC CMOS.

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Presentation on theme: "ASIC System Design Challenges: Floorplanning & Power Planning in today’s large chips Amin Farmahini Farahani Instructor: Prof. S. Mehdi Fakhraie ASIC CMOS."— Presentation transcript:

1 ASIC System Design Challenges: Floorplanning & Power Planning in today’s large chips Amin Farmahini Farahani Instructor: Prof. S. Mehdi Fakhraie ASIC CMOS Course University of Tehran, School of ECE May 2006 This is a class presentation. All data are copy righted to respective authors & companies as listed in the references and have been used here for educational purpose only.

2 Spring 2006ASIC - University of TehranPage 2 Outline Introduction FloorPlanning Power Planning Conclusion

3 Spring 2006ASIC - University of TehranPage 3 Outline Introduction FloorPlanning Power Planning Conclusion

4 Spring 2006ASIC - University of TehranPage 4 Introduction Technology allows us to build chips consisting of hundreds of millions of transistors. chips have several processors, large memories, peripherals, specific IP, and I/O. DSM forced us applying new attentions and methods. Design reuse—the use of pre- designed and pre-verified cores—is now the cornerstone of System Design (time to market). Fig. From [7]

5 Spring 2006ASIC - University of TehranPage 5 Motivation Floorplanning & power planning helps avoid IR drop and electromigration problems. The complexity of today’s designs have forced physical planning earlier in the flow.

6 Spring 2006ASIC - University of TehranPage 6 Definitions Macro (IP, Child Block) –design unit that can reasonably be viewed as a stand-alone subcomponent of a complete design. Subblock –a subcomponent of a macro (too small or specific to be a stand-alone design component). Soft macro –one that is delivered as synthesizable RTL code. Hard macro –one that is delivered as a GDSII file. It is fully designed, placed, and routed by the supplier ( layout level).

7 Spring 2006ASIC - University of TehranPage 7 Standard-cell vs. Mixed-mode Motivation: IP reuse Fig. From [6] Different blocks designed by different companies

8 Spring 2006ASIC - University of TehranPage 8 Outline Introduction FloorPlanning Power Planning Conclusion

9 Spring 2006ASIC - University of TehranPage 9 Hard Macro Placement Poor quality hard macro placement  failure in area, freq. As the number of logic gates and hard macro instances increases, placement becomes challenging (combination of hard macro and standard cells). hundred hard macro instances with different sizes and shapes.

10 Spring 2006ASIC - University of TehranPage 10 Hard Macro Placement (cont.) Some hard macros must be placed next to specific IO cells such as PLLs, DAC to allow wide connections. normal method: pre-place and “fix” these macros in specific locations (typically side bar) –Blockages for the rest of the design. –rectilinear core area for the rest of the design. –Routing bottlenecks. –Long routes for some macros.

11 Spring 2006ASIC - University of TehranPage 11 Simultaneous Std. Cell & Macro Placement Normal method do not result in optimized placement because both macros and standard cells are not considered simultaneously during wire-length optimization. Normal method ensures maximal contiguous (minimally fragmented) space for std. cells, but may result in long routes. So we need a better algorithm consider both std. cells and macros simultaneously. Tradeoff between standard cell space fragmentation and wire-length is necessary.

12 Spring 2006ASIC - University of TehranPage 12 Two Placement Standard cells surrounded by hard macros are unroutable; designs can be optimized to improve routablility by placement algorithms that do not create these types of areas [2].

13 Spring 2006ASIC - University of TehranPage 13 Automated placement results (JupiterXT TM ) Automated Grouping Fig. From [2]

14 Spring 2006ASIC - University of TehranPage 14 Pins Position Std. cells usually are approximated with all the pins at the center. length of a net is Manhattan distance between their centers. For larger macros, approximating the pins at the center introduces significant inaccuracies. Using the actual pin locations makes the optimization process more difficult. Also consider orientation problems.

15 Spring 2006ASIC - University of TehranPage 15 Outline Introduction FloorPlanning Power Planning Conclusion

16 Spring 2006ASIC - University of TehranPage 16 Power Planning Creation of the power network within a design Power planning is integrated with the overall design flow and must be taken into account early in the design process because: –# of pads may determine physical size (pad limited). –The power structures within the core area consume physical area. –The power grid topology effects top level routability, and also placement and routing within the child blocks. –The power structure effects functionality and reliability.

17 Spring 2006ASIC - University of TehranPage 17 Simplified Power Distribution Architecture (four basic elements) Fig. From [3]

18 Spring 2006ASIC - University of TehranPage 18 Power Network Elements Power Pad Power Rings –Form complete rings around the periphery of the die, around individual hard macros, or inside of hierarchical blocks. –higher-level Metal layers Power Straps/Trunks –Horizontal (strap) and vertical (trunk) metal wires placed in an array across the entire or section die. –higher level routing layers –typically uniformly distributed across the die. Power Rails –Is used to connect the standard cell power rails together, and or power trunks. –Low level, typically metal 1.

19 Spring 2006ASIC - University of TehranPage 19 Power Rings Floorplanning tool insert rings respecting available space in IO area. User specify width and spacing of the rings. rule of thumb: each side of the ring must carry a quarter of the current. divide overall power budget by four, using voltage, and current density for the metal layer determine the required width. It is best to create power and ground rings around any hard macro IP present in the design.

20 Spring 2006ASIC - University of TehranPage 20 Power and Ground Trunks Standard cell power rails are usually determined by the standard cell technology being used. Power rings and standard cell power rails have very little flexibility. straps and trunks have the most control and flexibility. Most important means to address detailed IR drop across the power network. A balance must be established between the need to retain routing resource for signal routes and the need to minimize IR drop.

21 Spring 2006ASIC - University of TehranPage 21 System Level Signal Integrity (SI) Timing Failures: crosstalk between nets can change the delays. Functional Failures: noise coupling between nets and/or cells can induce glitches. Fig. From [3]

22 Spring 2006ASIC - University of TehranPage 22 Signal Integrity Resolution: eliminate long parallel routes near the edge and at the top metal layer of a child block. Method: wiring keepout halo, partially around child block and partially at the top level. place buffers inside of the block close to the ports of the block. Thus, for top level signals the amount of wire that exists inside of the block is minimized.

23 Spring 2006ASIC - University of TehranPage 23 Outline Introduction FloorPlanning Power Planning Conclusion

24 Spring 2006ASIC - University of TehranPage 24 Conclusion Reuse attitude is required. Reuse permits complex designs. Well designed re-usable IP components enable successful design. Starting power integrity and floorplanning early is highly worthwhile in huge designs, because it avoids many problems in the later stages of the design flow.

25 Spring 2006ASIC - University of TehranPage 25 References 1. M. Keating, and P. Bricaud, “Reuse Methodology Manual for System-On-A-Chip Designs,” 3rd Ed., Kluwer Academic. 2. N. Kaul, and S. Kister, “Hard Macro Placement in Complex SoC Design,” Synopsys Inc., Sep. 2004, Available: 3. R. Rodgers, K. Knapp, and C. Smith, “Floorplanning Principles,” SNUG (Synopsys User Group Conference), San Jose, 2005, Available: 4. H. Piroozi, and K. Gopinathannair, “A Hierarchical Rail Analysis Flow for Multimillion Gate SoCs – Challenges and Solutions,” SNUG (Synopsys User Group Conference), San Jose, 2005, Available: 5. D. Stringfellow, and K. Knapp, “Power Integrity for SoCs: Power Planning and Signoff Flows,” Synopsys Inc., Nov. 2005, Available: 6. S. Adya, and I. Markov, “Combinatorial techniques for mixed mode placement,” University of Michigan, Available: 7. JupiterIO: Concurrent Die/Package IO Planning, Synopsys Inc., S. Idgunji, S. Lloyd, R. Mitchell, R. Spillman, and J. Young, “Design Planning Strategies to Improve Physical Design Flows—Floorplanning and Power Planning,” Synopsys Inc., Aug. 2003, Available: 9. L. L. Azuara, and R. Dorsch, “Design for Reuse in embedded system design,” Available:

26 Spring 2006ASIC - University of TehranPage 26 Thanks Thanks for putting up with all my talk ?Any Question?


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