May 8, USB 2.0 Hub Repeater Jon Lueker Intel Corporation

May 8, Agenda w Connectivity w Timing parameters w Microframe handling

May 8, Packet Connectivity Enabled Port Port not Enabled Downstream Connectivity Downstream Ports Upstream Port Upstream Connectivity Idle (No Connectivity) Paradigm Unchanged; But Behavioral Changes

May 8, Level and Timing Regeneration in USB 2.0 w USB 2.0 hub must reclock data – Use of elasticity buffer u Bit delay is cumulative u Bit jitter is not cumulative – SOP and EOP signal (level and timing) regenerated u Field lengths not preserved Bit Timing Is Regenerated in USB 2.0 Port Selector State Machine Rcv_stream Squelch Xmt_Clk Rcv_Clk Xmt_stream Data Recovery Elasticity Buffer

May 8, Repeater Elasticity Buffer(EB) w EB accounts for clock differences between rcv and xmt – +/- 500 ppm + jitter -> +/- 12 bits u 1K byte packet -> 9644 bits -> +/- 10 bits u Timing margin (including host jitter) -> +/- 2 bits – EB size needs at least 24 bits to prevent over/underflow u Xmt clock may be slower or faster than rcv clock u Xmt starts when EB has at least 12 bits – Resync during interpacket gap EB Size Must Account for Clock Accuracy and Host Jitter Rcv_data Xmt_clk Rcv_clk Xmt_data Data Recovery Elasticity Buffer Depth=24, Xmt Start at 12

May 8, Port Selector State Machine Setup of packet connectivity is qualified by SORP EBEmptied Inactive Enable Transmit Not Packet Squelch EOI&SORP !Squelch Priming !Squelch&EOI&!SORP Rx_Bus_Reset Squelch&EOI&!SORP

May 8, SYNC Sacrifice w Each repeater may consume up to 4 bits of SYNC – Rcv_stream ignored when squelch is active w 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 SYNC Sacrifice Budget Is for Entire Repeater Path Port Selector State Machine Rcv_stream Squelch Xmt_Clk Rcv_Clk Xmt_stream Data Recovery Elasticity Buffer

May 8, EOP Dribble w 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 w Each repeater may add at most 4 bits – 20 bits of dribble may result through 5 tiers Connectivity Teardown Does NOT Require EOP Detection Port Selector State Machine Rcv_stream Squelch Xmt_Clk Rcv_Clk Xmt_stream Data Recovery Elasticity Buffer

May 8, Latency w Is defined as delay through repeater at end of SYNC – Max allowed is 36 bits – EB contributes at least 12 bits Rcv _data Xmt_clkXmt_clk Rcv_clkRcv_clk Xmt_dataXmt_data Data Recovery Elasticity Buffer Depth=24, Xmt Start at 12 Latency Requirement Is Stringent

May 8, Resume Connectivity of Awake Hub Paradigm Unchanged; But Specific Behavioral Changes Paradigm Unchanged; But Specific Behavioral Changes Command Downstream Ports Upstream Port RWU Enabled Port Port Disabled Port Suspended RWU is recognized only if persistent

May 8, Resume Connectivity of Suspended Hub Paradigm Unchanged; But Specific Behavioral Changes Paradigm Unchanged; But Specific Behavioral Changes Bus States at DS Ports Are Filtered for persistence before propagation Downstream Connectivity Downstream Ports Upstream Port Upstream Connectivity Enabled Port Port Disabled or Suspended Suspended Port Enabled or Suspended

May 8, Function Hub Delay Hub 1Hub 2Hub 3Hub 4Hub 5 Propagation Delay Host Controller 32 bit SYNC 0 bit EOP Dribble 28 bit SYNC 4 bit EOP Dribble 12 bit SYNC 20 bit EOP Dribble Topology w Topology paradigm unchanged w Changes in delays w Changes in SYNC and EOP fields 5 Non-Root Hubs Is Still the Limit

May 8, Microframe Jitter w Microframe jitter added by repeater must be controlled – Entire repeater microframe jitter budget is 0 to 5 bits – Cumulative jitter through 4 repeaters < 20 bit times – Fifth hub quantization jitter < 16 bits Microframe Jitter Requirement Is VERY Stringent

May 8, SOFEOF1EOF2EOF EOF1, EOF2 w 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 downstream babbler is shut down – EOF1 is 560 bits before EOF – EOF2 is 64 bits before EOF EOF Usage Similar to USB 1.X

May 8, Conclusion w Connectivity – Packet Ô SOP filter, EB, SYNC/EOP distortion – Resume Ô Filtering w Timing parameters – Latency, Jitter w Microframe handling – EOF1, EOF2