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Logic synthesis from concurrent specifications

This document provides an in-depth exploration of logic synthesis based on concurrent specifications, primarily focusing on asynchronous controllers and interfaces. It outlines crucial components of the synthesis flow, including state graphs, next-state functions, state encoding, and implementability conditions for speed-independent circuits. Various advanced topics are reviewed, demonstrating applications in practical designs like the VME bus controller. This work serves as a valuable resource for designers aiming to derive hazard-free circuits with specified delay models.

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Logic synthesis from concurrent specifications

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  1. Logic synthesis from concurrent specifications Jordi Cortadella Universitat Politecnica de CatalunyaBarcelona, Spain In collaboration with M. Kishinevsky, A. Kondratyev, L. Lavagno and A. Yakovlev

  2. Outline • Overview of the synthesis flow • Specification • State graph and next-state functions • State encoding • Implementability conditions • Speed-independent circuit • Complex gates • C-element architecture • Review of some advanced topics

  3. Book and synthesis tool • J. Cortadella, M. Kishinevsky, A. Kondratyev,L. Lavagno and A. Yakovlev,Logic synthesis for asynchronouscontrollers and interfaces,Springer-Verlag, 2002 • petrify:http://www.lsi.upc.es/petrify

  4. Design flow Specification(STG) Reachability analysis State Graph State encoding SG withCSC Boolean minimization Next-state functions Logic decomposition Decomposed functions Technology mapping Gate netlist

  5. Specification x x y y z z z+ x- x+ y+ z- y- Signal Transition Graph (STG)

  6. x y z z+ x- x+ y+ z- y- Token flow

  7. xyz 000 x+ 100 y+ z+ z+ x- 110 101 x- x+ y+ z- y- y+ z+ 001 111 y- y+ x- 011 z- 010 State graph

  8. xyz 000 x+ 100 y+ z+ 110 101 x- y- y+ z+ 001 111 y+ x- 011 z- 010 Next-state functions

  9. Gate netlist x y z

  10. Design flow Specification(STG) Reachability analysis State Graph State encoding SG withCSC Boolean minimization Next-state functions Logic decomposition Decomposed functions Technology mapping Gate netlist

  11. DSr LDS LDTACK D DTACK Read Cycle VME bus Bus Data Transceiver Device D DSr LDS VME Bus Controller DSw LDTACK DTACK

  12. STG for the READ cycle DSr+ DTACK- LDS+ LDTACK+ D+ DTACK+ DSr- D- LDTACK- LDS- D LDS DSr VME Bus Controller LDTACK DTACK

  13. LDTACK- DTACK- DTACK- LDTACK- LDS- LDS- Choice: Read and Write cycles DSr+ DSw+ LDS+ D+ LDTACK+ LDS+ D+ LDTACK+ DTACK+ D- DSr- DTACK+ D- DSw-

  14. DTACK- DSr+ DSw+ LDS+ D+ LDTACK+ LDS+ LDTACK- D+ LDTACK+ DTACK+ D- LDS- DSr- DTACK+ D- DSw- Choice: Read and Write cycles

  15. Circuitsynthesis • Goal: • Derive a hazard-free circuitunder a given delay model andmode of operation

  16. Speed independence • Delay model • Unbounded gate / environment delays • Certain wire delays shorter than certain paths in the circuit • Conditions for implementability: • Consistency • Complete State Coding • Persistency

  17. Design flow Specification(STG) Reachability analysis State Graph State encoding SG withCSC Boolean minimization Next-state functions Logic decomposition Decomposed functions Technology mapping Gate netlist

  18. STG for the READ cycle DSr+ DTACK- LDS+ LDTACK+ D+ DTACK+ DSr- D- LDTACK- LDS- D LDS DSr VME Bus Controller LDTACK DTACK

  19. LDS + LDS = 0 LDS - LDS = 1 Binary encoding of signals DSr+ DTACK- LDS+ LDTACK- LDTACK- LDTACK- DSr+ DTACK- LDS- LDS- LDS- LDTACK+ DSr+ DTACK- D+ D- DTACK+ DSr-

  20. 01100 00110 Binary encoding of signals 10000 DSr+ DTACK- LDS+ LDTACK- LDTACK- LDTACK- DSr+ DTACK- 10010 LDS- LDS- LDS- LDTACK+ DSr+ DTACK- 10110 01110 10110 D+ D- DTACK+ DSr- (DSr , DTACK , LDTACK , LDS , D)

  21. ER (LDS+) LDS+ QR (LDS-) LDS- LDS- LDS- ER (LDS-) QR (LDS+) Excitation / Quiescent Regions

  22. LDS+ LDS- LDS- LDS- 10110 10110 Next-state function 0  1 0  0 1  1 1  0

  23. DTACK DSr DTACK DSr D LDTACK D LDTACK 00 00 01 01 11 11 10 10 00 00 01 01 11 11 10 10 Karnaugh map for LDS LDS = 1 LDS = 0 - - - 0 0 - 1 1 - - - - - - - - 1 1 1 - - - - - 0 0 - 0 0 0 - 0/1?

  24. Design flow Specification(STG) Reachability analysis State Graph State encoding SG withCSC Boolean minimization Next-state functions Logic decomposition Decomposed functions Technology mapping Gate netlist

  25. DSr+ DSr+ DSr+ Concurrency reduction LDS+ LDS- LDS- LDS- 10110 10110

  26. Concurrency reduction DSr+ DTACK- LDS+ LDTACK+ D+ DTACK+ DSr- D- LDTACK- LDS-

  27. State encoding conflicts LDS+ LDTACK- LDS- LDTACK+ 10110 10110

  28. CSC+ CSC- Signal Insertion LDS+ LDTACK- LDS- LDTACK+ 101101 101100 D- DSr-

  29. Design flow Specification(STG) Reachability analysis State Graph State encoding SG withCSC Boolean minimization Next-state functions Logic decomposition Decomposed functions Technology mapping Gate netlist

  30. Complex-gate implementation

  31. Implementability conditions • Consistency • Rising and falling transitions of each signal alternate in any trace • Complete state coding (CSC) • Next-state functions correctly defined • Persistency • No event can be disabled by another event (unless they are both inputs)

  32. Implementability conditions • Consistency + CSC + persistency • There exists a speed-independent circuit that implements the behavior of the STG(under the assumption that ay Boolean function can be implemented with one complex gate)

  33. a- c+ a 100 000 001 b c b+ b+ Persistency a c b is this a pulse ? Speed independence  glitch-free output behavior under any delay

  34. a+ 0000 a+ b+ 1000 b+ 1100 a- a- 0100 c+ c+ 0110 d+ d- d+ 0111 a+ a+ 1111 b- b- 1011 a- c- a- c- 0011 1001 a- c- d- 0001

  35. ab 0000 cd 00 01 11 10 a+ 1000 0 0 0 0 00 b+ 1100 1 0 a- 01 0100 c+ 1 1 1 1 0110 11 d- d+ 0111 1 10 a+ 1111 b- 1011 a- c- 0011 1001 a- c- 0001 ER(d+) ER(d-)

  36. 0000 a+ 1000 b+ 1100 a- 0100 c+ 0110 d- d+ 0111 a+ 1111 b- 1011 a- c- 0011 1001 a- c- 0001 ab cd 00 01 11 10 0 0 0 0 00 1 0 01 1 1 1 1 11 1 10 Complex gate

  37. S z C R Implementation with C elements • • •  S+  z+  S-  R+  z-  R-  • • • • S (set) and R (reset) must be mutually exclusive • S must cover ER(z+) and must not intersect ER(z-)  QR(z-) • R must cover ER(z-) and must not intersect ER(z+)  QR(z+)

  38. 0000 a+ 1000 b+ 1100 a- 0100 c+ 0110 d- d+ 0111 a+ 1111 b- 1011 a- c- 0011 1001 a- c- 0001 ab cd 00 01 11 10 0 0 0 0 00 1 0 01 1 1 1 1 11 1 10 S d C R

  39. 0000 a+ 1000 b+ 1100 a- 0100 c+ 0110 d- d+ 0111 a+ 1111 b- 1011 a- c- 0011 1001 a- c- 0001 ab cd 00 01 11 10 0 0 0 0 00 1 0 01 1 1 1 1 11 1 10 S d C R Monotonic covers

  40. C-based implementations S c d d C C R b a c weak c d weak d a a b generalized C elements (gC)

  41. Speed-independent implementations • Implementability conditions • Consistency • Complete state coding • Persistency • Circuit architectures • Complex (hazard-free) gates • C elements with monotonic covers • ...

  42. y- y- 1001 z- w- 1000 0001 w+ y+ w- z- x+ z- w- w+ 1010 0000 0101 w- y+ x+ z- y+ x+ x- 0010 0100 x- x+ y+ z+ 0110 z+ Synthesis exercise 1011 0011 0111 Derive circuits for signals x and z (complex gates and monotonic covers)

  43. y- 1001 z- w- 1000 0001 w+ y+ w- z- x+ 1010 0000 0101 w- y+ x+ z- 0010 0100 x- x+ y+ z+ 0110 Synthesis exercise 1011 wx yz 00 01 11 10 - 1 0 1 00 0011 - 1 0 1 01 - 0 0 0 11 - 1 1 0 10 0111 Signal x

  44. y- 1001 z- w- 1000 0001 w+ y+ w- z- x+ 1010 0000 0101 w- y+ x+ z- 0010 0100 x- x+ y+ z+ 0110 Synthesis exercise 1011 wx yz 00 01 11 10 - 0 0 0 00 0011 - 0 0 0 01 - 1 1 1 11 - 1 0 0 10 0111 Signal z

  45. Logic decomposition: example y- y- 1001 1011 z- w- 1000 0001 w+ y+ w- z- x+ z- w- w+ 1010 0000 0101 0011 w- y+ x+ z- y+ x+ x- 0010 0100 x- x+ y+ z+ 0110 0111 z+

  46. y- 1001 1011 z- w- 1000 0001 w+ y+ w- z- x+ 1010 0000 0101 0011 w- y+ x+ z- C 0010 0100 x- x+ y+ z+ C 0110 0111 yz=0 yz=1 Logic decomposition: example x y- y w 1001 1011 z- z w- y 1000 0001 w+ y+ z w- z- x+ x w 1010 0000 0101 0011 w- y+ x+ z- w z y 0010 0100 x- z x+ y+ z+ y 0110 0111 x z y

  47. C C Logic decomposition: example s=1 x y- w s 1001 1011 y z- s- z w+ 1001 1000 z- s- y+ w- x w 0011 1000 0001 1010 y+ s- w- z- x+ w x- z y 1010 0000 0101 z w- y+ x+ z- 0111 0010 0100 y s+ x+ y+ x z s=0 z+ 0111 y 0110

  48. Logic decomposition: example s=1 y- y- 1001 1011 z- s- s- w+ 1001 1000 z- s- y+ w- z- w- w+ 0011 1000 0001 1010 y+ s- w- z- x+ x- 1010 0000 0101 y+ x+ x- w- y+ x+ z- 0111 0010 0100 s+ s+ x+ y+ z+ s=0 z+ 0111 0110

  49. Speed-independent Netlist DSr+ DTACK- LDS+ LDTACK+ D+ DTACK+ DSr- D- LDTACK- LDS- D DTACK LDS map csc DSr LDTACK

  50. LDTACK- before DSr+ SLOW FAST Adding timing assumptions DSr+ DTACK- LDS+ LDTACK+ D+ DTACK+ DSr- D- LDTACK- LDS- D DTACK LDS map csc DSr LDTACK

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