USB 2.0 Hub Repeater

2. May 16, 2000 2 USB 2.0 Hub Repeater Venkat Iyer Intel Corporation

3. May 16, 2000 3 Agenda Connectivity Timing parameters Transaction translator synchronization Microframe handling Hub arch – u port, d port, rptr; sm for each; controller because hub is a USB device; TT is new Conn – packet and resume Understand timing parameters of 2.0 rptr How TT generates SOF for fs/ls ports; how they stay in sync Microframe sync and EOF behavior and timingsHub arch – u port, d port, rptr; sm for each; controller because hub is a USB device; TT is new Conn – packet and resume Understand timing parameters of 2.0 rptr How TT generates SOF for fs/ls ports; how they stay in sync Microframe sync and EOF behavior and timings

4. May 16, 2000 4 Repeater Behavior Changes for USB 2.0 Speed assertion and detection during reset Changes to synchronize TT SOFs to host microframes Disconnect detection using long EOP Noise immunity enhanced Start of packet filtered RWU and disconnect filtered End of resume generation Resume ended with Idle state at high-speed port Resume ended with EOP at full/low-speed port New state and behaviors for testing electrical parameters

5. May 16, 2000 5 Packet Connectivity

6. State Machines

7. May 16, 2000 7 Hub Repeater State Machinefor Packet Connectivity

8. May 16, 2000 8 Repeater State Machine Input Changes (SOHP)SOP (After SORP identified) on the transition from the Idleto K state on a port (HEOP)EOP (EBEmptied signal from port selector state machine)one bit time after SE0 to Idle state on port (Transition at EOI from SendEOR state in downstream facing port state machine EOITR from upstream facing port receiver state machine)

9. May 16, 2000 9 Some Definitions Signal quality = signal levels and signal timings Signal levels Start of packet and end of packet are most impacted Differential level is less impacted than common-mode level Signal timings Rise/fall times are preserved Bit interval Delay is cumulated through repeaters Jitter NOT cumulated through repeaters Packet/microframe interval Delay is cumulated through repeaters Jitter is cumulated through repeaters

10. May 16, 2000 10 Level and Timing Regeneration in USB 2.0 USB 2.0 hub must reclock data Use of elasticity buffer Bit delay is cumulative Bit jitter is not cumulative SOP and EOP signal (level and timing) regenerated Field lengths not preserved

11. May 16, 2000 11 Repeater Elasticity Buffer(EB) EB accounts for clock differences between rcv and xmt +/- 500 ppm + jitter -> +/- 12 bits 1K byte packet -> 9644 bits -> +/- 10 bits Timing margin (including host jitter) -> +/- 2 bits EB size needs at least 24 bits to prevent over/underflow Xmt clock may be slower or faster than rcv clock Xmt starts when EB has at least 12 bits Resync during interpacket gap

12. May 16, 2000 12 Port Selector State Machine

13. May 16, 2000 13 Collision Detection USB 1.x hubs look for SOP when connectivityis established Garbling of first packet is recommended Blocking of second packet is allowed USB 2.0 hubs could use SOHP in place of SOP Requires duplication of port selector logic Unsquelch signal can be used instead of SOHP Single port selector for hub

14. May 16, 2000 14 SYNC Sacrifice Each repeater may consume up to 4 bits of SYNC Rcv_stream ignored when squelch is active 5 hub tiers may consume 20 bits of SYNC SYNC field starts out as 32 bits Device will still see at least 12 bits of SYNC

15. May 16, 2000 15 EOP Dribble Connectivity torn down on squelch Squelch delay can be up to 4 bits Results in EOP dribble with random bits Unlike USB 1.1, there is no data dribble Each repeater may add at most 4 bits 20 bits of dribble may result through 5 tiers

16. May 16, 2000 16 Latency Is defined as delay through repeater atend of SYNC Max allowed is 36 bits EB contributes at least 12 bits

17. May 16, 2000 17 Downstream Packet Connectivity

18. May 16, 2000 18 Upstream Packet Connectivity

19. May 16, 2000 19 Resume Connectivityof Awake Hub

20. May 16, 2000 20 Resume Connectivityat Awake Hub

21. May 16, 2000 21 Resume Connectivityof Suspended Hub

22. May 16, 2000 22 Hub State Machinesfor RWU

23. May 16, 2000 23 Hub Repeater for Resume

24. Resume Timings

25. May 16, 2000 25 Downstream Resume Connectivity

26. Resume atFull/Low-Speed Device

27. Resume atHigh-Speed Device

28. May 16, 2000 28 Topology Topology paradigm unchanged Changes in delays Changes in SYNC and EOP fields

29. May 16, 2000 29 SE1

30. May 16, 2000 30 Microframe Jitter Microframe jitter is an important parameter Host generates microframes at 125 us (nominal) microframe-to-microframe jitter at host < 4 bits Entire repeater microframe jitter 0 to 5 bits Cumulative jitter through 4 repeaters < 20 bit times Fifth hub quantization jitter < 16 bits Microframe-to-microframe jitter at a frame timer< 40 bits(or 83.3 ns)

31. May 16, 2000 31 Transaction Translator SOF TT derives its SOF from local frame timer whichis synced to host frame timer USB 1.x requirement of frame-to-frame jitter< 42 ns is satisfied All frame periods synced to host frame period

32. May 16, 2000 32 TT Suspend SOF generation should cease within 250 usof idle at upstream port All ports of a hub go into suspend within 250 usof each other OS to ensure that all pending TT transactionscompleted prior to hub being suspended

33. May 16, 2000 33 EOF Advancement EOF advanced by the decode delay Needed because SOF PID decode can vary from 40 to 192 bits With advancement, downstream hubs have later EOFs Max EOF spread is 216 bits Accumulated repeater latency : 144 bits Accumulated cable delay : 72 bits

34. May 16, 2000 34 EOF2 at 64 EOF2 must be at least 54 bits before EOF Microframe timer skew : -2 to +38 bits Host frame jitter : +/- 2 bits repeater frame jitter : 36 bits Quantization : 16 bits

35. May 16, 2000 35 EOF1 at 560 EOF1 must be at least 544 bits before EOF EOF2 offset : 64 bits EOP propagation delay : 216 bits Bus idle time : 8 bits

36. May 16, 2000 36 Testing

37. May 16, 2000 37 Conclusion Connectivity Packet SOP filter, EB, SYNC/EOP distortion Resume Filtering, EOP synthesis Testing Timing parameters Latency, interpacket gap TT frame sync Jitter, suspend Microframe handling Frame advancement, EOF1/2 Hub arch – u port, d port, rptr; sm for each; controller because hub is a USB device; TT is new Conn – packet and resume Understand timing parameters of 2.0 rptr How TT generates SOF for fs/ls ports; how they stay in sync Microframe sync and EOF behavior and timingsHub arch – u port, d port, rptr; sm for each; controller because hub is a USB device; TT is new Conn – packet and resume Understand timing parameters of 2.0 rptr How TT generates SOF for fs/ls ports; how they stay in sync Microframe sync and EOF behavior and timings

38. May 16, 2000 38 Backup

39. May 16, 2000 39 Downstream PortState Machine

40. May 16, 2000 40 Upstream PortState Machines

41. May 16, 2000 41 Repeater State Machine

42. May 16, 2000 42 Port Selector State Machine

43. May 16, 2000 43 Level and Timing Regeneration in USB 1.x USB 1.x regenerates signal levels only Flow through signaling; combinational delay Bit delay is cumulative Bit jitter is cumulative SOP and EOP timings degraded

44. May 16, 2000 44 EB Latency Data transmission can start when EB has 12 bits This model accounts for slower or faster clock Latency is at least 12 bits EB latency must be included in total hub latency budget

45. May 16, 2000 45 EB Resync Host interpacket gap has to be long enough to empty EB Measured from end of EOP to start of sync at A conn EB depth + EOP dribble + margin 24 + 24 + 40 = 88 bits Repeater has to correctly repeat if IPG >=32 bits Bit-stuff-error has no effect on repeater function

46. May 16, 2000 46 Start of Connectivity Differs from USB 1.x connectivity which starts on edge USB 2.0 connectivity starts after pattern JKJK / KJKJ pattern detection Pattern detection provides noise immunity Repeating can start with pattern bits State machine Per port or per hub Integrating with EB possibleIntegrating with EB possible

47. May 16, 2000 47 Turnaround Time Defined from EOP to start of sync EOP and sync are from different signaling sources Measured at source of second packet Max is 192 bits (+52 ns with integrated cable) Includes time needed for parallelizing and checking Min is 8 bits of bus quiescent time Allows all xcvr circuits to return to quiescent state

48. May 16, 2000 48 Timeout Defined as wait time before response packet presumed lost Maximum response time related to timeout Measured from end of EOP to start of sync Measured at source of EOP signaling Round trip cable delay + hub round trip latency+ turnaround time Period is comparable to USB 1.x

49. May 16, 2000 49 Timeout Maximum response time calculation 12 max length cable delays (6 in each direction) = 312ns 10 max delay hubs (5 in each direction) = 40ns + 360 bit times 1 max device response time = 192 bit times Maximum response time = 352ns + 552 bit time This is 721 bits Timeout after 736 bits but before 816 bits

50. May 16, 2000 50 Microframe Timer Synchronization

51. May 16, 2000 51 EOF1, EOF2 EOF1, EOF2 usage same in USB 1.x EOF1 used to tear down all upstream connectivity EOF2 is used to detect babble EOF1 is before EOF2 so only immediate downstreambabbler is shut down EOF1 is 560 bits before EOF EOF2 is 64 bits before EOF

52. May 16, 2000 52 Host Behavior at EOF Host must not provoke a response from device which causesa device to be transmitting at EOF2 Host must ensure that no transactions are pending at EOF1of any hub Host can achieve this by completing last transaction before EOF1