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Analysis and avoidance of crosstalk in on-chip buses

Analysis and avoidance of crosstalk in on-chip buses. Hot Interconnects 2001 C. Duan, A. Tirumala, S. P. Khatri. Outline. Crosstalk taxonomy Eliminating 3C and 4C Eliminating 4C Experimental results Conclusions. Crosstalk taxonomy - 4C. Crosstalk taxonomy - 3C. Crosstalk taxonomy - 2C.

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Analysis and avoidance of crosstalk in on-chip buses

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  1. Analysis and avoidance of crosstalk in on-chip buses Hot Interconnects 2001 C. Duan, A. Tirumala, S. P. Khatri

  2. Outline • Crosstalk taxonomy • Eliminating 3C and 4C • Eliminating 4C • Experimental results • Conclusions

  3. Crosstalk taxonomy - 4C

  4. Crosstalk taxonomy - 3C

  5. Crosstalk taxonomy - 2C

  6. Crosstalk taxonomy - 1C

  7. 1 0 0 1 1 0 Forbidden vectors

  8. 1 1 0 0 1 1 Forbidden vectors removal • Eliminating 4C crosstalk • trivial • Eliminating 3C crosstalk

  9. Encoding techniques • n-bit inputs –2n vectors • Tg(x)– vectors which are not forbidden • If Tg(n+m) > 2n • Use n+m bits to represent n bits with maximum 2C crosstalk

  10. Recurrence relation • T(n)– number of total vectors • Tb(n)– number of forbidden vectors • Tg(n)– number of legal vectors • Tgg(n) – Tg(n) | vn-1=vn • Tgb(n) – Tg(n) | vn-1vn

  11. Recurrence example T(2) = 4 T(3) = 8 Tg(2) = 4 Tg(3) = 6 Tgg(2) = 2 Tgg(3) = 4 Tgb(2) = 2 Tgb(3) = 2 Tb(2) = 0 Tb(3) = 2 000 001 010 011 100 101 110 111 00 01 10 11

  12. Recurrence formula • T(n) = 2T(n-1) • Tg(n) = 2Tgg(n-1)+Tgb(n-1) • Tgg(n) = Tgg(n-1)+Tgb(n-1) • Tgb(n) = Tgg(n-1) • Tb(n) = 2Tb(n-1)+Tgb(n-1)

  13. Overhead

  14. An encoding example • 4-5 encoder to eliminate 3C and 4C

  15. I0-I3 E1 O0-O4 E2 I4-I7 O5-O9 16 Bits E3 26 Bits I8-I11 O10-O14 E4 I12-I15 O15-O19 GCB1-GCB4 G1 O20-O24 O25 Boundary forbidden bit removal • (11110) (11100) • Additional group complement bit (GCB) • (11110) (00011) • GCBs form another groups

  16. Fallacy – time variant • Forbidden vector removal • only concern about the current state • Real case • Phase transitions induce crosstalk effect

  17. Eliminating 4C crosstalk • 3-bit group • Additional Group Complement Bit (GCB) • (010 101)k (101 011)k+1 • (0100 1010)k (0101 0110)k+1 • Solving complement bit transition • (0100 1010)k (0101 1001)k+1 • Ripple effect

  18. Improved encoder • Check the first and the last 2 bits • Complement group once occurring 2C • (010 101)k (101 011)k+1 • (0100 1010)k (0101 1001)k+1 • No ripple effect

  19. Experimental results

  20. Experimental results

  21. Conclusions • Bus encoding for crosstalk avoidance • 62.5% overhead for 3C and 4C elimination • 33% overhead for 4C elimination

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