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May 16, 2000. 2. USB 2.0 Hub Repeater. Venkat IyerIntel Corporation. May 16, 2000. 3. Agenda. ConnectivityTiming parametersTransaction translator synchronization Microframe handling. . . . . Port 1. Port 2. Port N. . .... Downstream Ports. Port 0. . Upstream Port. . . Hub Controller. . . . . .
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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