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Elastic Systems

This paper investigates the concept of elasticity in system design, highlighting both asynchronous and synchronous pipeline structures. It draws on historical references, including da Vinci's catapult, David Muller's pipeline from the late 1950s, and key theories on latency-insensitive systems. Practical implications of time uncertainty and the need for modularity are discussed alongside behavioral equivalence in elastic circuits. The study emphasizes advancements in handshake protocols, communication channels, and storage mechanisms, providing insights for future developments in integrated circuit design.

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Elastic Systems

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  1. Elastic Systems JordiCortadellaUniversitatPolitècnica de CatalunyaMarc Galceran-OmsUniversitatPolitècnica de Catalunya Mike Kishinevsky Intel Corp.

  2. Elasticity Leonardo da Vinci’s catapult

  3. Asynchronous elastic pipeline ReqIn ReqOut C C C C AckOut AckIn David Muller’s pipeline (late 50’s) Sutherland’s Micropipelines (1989)

  4. The specification of a complex system is usuallyasynchronous (functional units, messages, queues, …), … however the clock appears when we move downto the implementation levels (Bill Grundmann, 2004)

  5. Asynchronous elasticity req ack CLK

  6. Synchronous elasticity valid stop CLK Latency-insensitive systems (Carloni et al., 1999) Synchronous handshake circuits (Peeters et al, 2001) Synchronous elastic systems (Cortadella et al., 2006) Latency-Insensitive Bounded Dataflow Networks (Vijayaraghavan et al., 2009) Synchronous emulation of asynchronous circuits (O’Leary, 1997)

  7. Many systems are already elastic AMBA AXI bus protocol Handshake signals

  8. Time uncertainty in chip design How manycycles ?

  9. Why elastic circuits now ? • Need to live with time uncertainty • Need to formalize time uncertainty • For synthesis • For verification • Need for modularity

  10. Behavioral equivalence in Elastic Circuits … … + 4 7 1 … 4 8 3 0 1 2 … … 4 + 7 1 e … 3 4 8 0 1 2

  11. Behavioral equivalence in Elastic Circuits … … + 4 7 1 … 4 8 3 0 1 2 … … 4 + 7 1 e … 3 4 8 0 1 2 bubble token Traces a preserved after hiding bubbles (stream-based equivalence)

  12. Unpipelined system

  13. Pipelined system

  14. Write Buffer

  15. Communication channel sender receiver Data Data Long wires: slow transmission

  16. Data Pipelined communication sender receiver Data

  17. Data Pipelined communication sender receiver Data

  18. The Valid bit sender receiver Data Data Valid Valid

  19. sender receiver Data Data Valid Valid Stop Stop 0 0 0 0 0 The Stop bit

  20. sender receiver Data Data Valid Valid Stop Stop 0 0 0 1 1 The Stop bit

  21. sender receiver Data Data Valid Valid Stop Stop 0 0 1 1 1 The Stop bit

  22. sender receiver Data Data Valid Valid Stop Stop 1 1 1 1 1 The Stop bit Back-pressure

  23. sender receiver Data Data Valid Valid Stop Stop 1 1 1 1 0 The Stop bit

  24. sender receiver Data Data Valid Valid Stop Stop 0 0 0 0 0 The Stop bit

  25. sender receiver Data Data Valid Valid Stop Stop 0 0 0 0 0 The Stop bit

  26. sender receiver Data Data Valid Valid Stop Stop 0 0 0 0 0 The Stop bit

  27. sender receiver Data Data Valid Valid Stop Stop 0 0 0 0 1 The Stop bit Long combinational path

  28. sender receiver shell shell main main main pearl pearl aux aux aux Carloni’s relay stations (double storage)

  29. sender receiver shell shell main main main pearl pearl aux aux aux Carloni’s relay stations (double storage)

  30. sender receiver shell shell main main main pearl pearl aux aux aux Carloni’s relay stations (double storage)

  31. sender receiver shell shell main main main pearl pearl aux aux aux Carloni’s relay stations (double storage)

  32. sender receiver shell shell main main main pearl pearl aux aux aux Carloni’s relay stations (double storage)

  33. sender receiver shell shell main main main pearl pearl aux aux aux Carloni’s relay stations (double storage)

  34. sender receiver shell shell main main main pearl pearl aux aux aux Carloni’s relay stations (double storage)

  35. sender receiver shell shell main main main pearl pearl aux aux aux Carloni’s relay stations (double storage)

  36. sender receiver shell shell main main main pearl pearl aux aux aux Carloni’s relay stations (double storage) • Handshakes with short wires • Double storage required

  37. Flip-flops vs. latches sender receiver FF FF 1 cycle

  38. Flip-flops vs. latches sender receiver H L H L 1 cycle

  39. Flip-flops vs. latches sender receiver H L H L 1 cycle

  40. Flip-flops vs. latches sender receiver H L H L 1 cycle

  41. Flip-flops vs. latches sender receiver H L H L 1 cycle

  42. Flip-flops vs. latches sender receiver H L H L 1 cycle Flip-flops already have a double storage capability, but …

  43. Flip-flops vs. latches sender receiver H L H L 1 cycle Not allowed in conventional FF-based design !

  44. H L H L Flip-flops vs. latches sender receiver 1 cycle Let’s make the master/slave latches independent

  45. H L H L Flip-flops vs. latches sender receiver ½ cycle ½ cycle Let’s make the master/slave latches independent Only half of the latches (H or L) can move tokens

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