Chapter 11: The High-Speed Signaling Environment

The high-speed signaling interface must include the necessary features to support the appropriate upstream port speed and perform a variety of other signaling events. The high-speed interface must be capable of:

•Dynamic transition between different interface speeds

•High-speed device detection (handshake between high-speed hub and device)

•Detecting high-speed device disconnect (hub ports only)

•Signaling (hubs only) and detecting high-speed reset

•Supporting high-speed differential signaling (including impedance matching)

•Signaling and detecting high-speed start of packet

•Signaling and detecting high-speed EOP

•Supporting suspend and resume operation and signaling

Each of the signaling functions listed above will be discussed later in this chapter. Figure 11-2 illustrates the high-speed transceiver interface. The interface components in the lighter shade are used in the 1.x transceivers, and the darker shade represents components that have been added to support high-speed signaling. The differential receivers are illustrated with both shades because in this example they operate at all three speeds.

Detecting High-Speed Device Attachment

High-speed hub ports must be able to detect when a low-speed, full-speed, or high-speed device has been connected to the port. High-speed devices initially appear as full-speed devices when attached to a high-speed port. The highspeed port and the high-speed devices must then perform a handshake to identify the high-speed device. If the handshake fails, the high-speed device defaults to full-speed operation. The sequence of events is illustrated in Figure 11-3 and presumes that power has already been applied to the port. This sequence is identical to that which occurs when a full-speed device is attached except for the handshake (called the chirp sequence) that occurs during device RESET.

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Figure 11-2: High-Speed signaling Interface

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Chapter 11: The High-Speed Signaling Environment

Figure 11-3: Sequence of Events from Device Connect to High-Speed Operation

Initial Device Detection

Fulland high-speed devices both have a 1.5KΩ on the D+ line. When the device is connected, power is applied to the cable, the device, and the pull-up on D+, causing the voltage to rise above VIH at the hub receiver. Software then polls the hub and detects full-speed device attachment.

Device Reset and the Chirp Sequence

After software detects that a full-speed device is connected, it issues RESET to the hub via the ResetPort command, which causes the hub to drive a SE0 (both D+ and D- low) for >10ms. If a high-speed capable device is attached, the chirp sequence begins. Figure 11-4 on page 223 depicts the chirp sequence. Each step in the chirp sequence is detailed in the following enumerated list:

1.Hub drives RESET, which is T0 for the chirp sequence.

2.The high-speed device detects RESET and signals a Chirp K. signaling

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Chirp K is done by sourcing current into the D- line via the high-speed current driver. This Chirp K must be signaled for greater than 1ms and can remain asserted no longer than 7ms after T0.

3.While driving the full-speed RESET, the hub’s high-speed receiver is acti-

vated and awaits the detection of Chirp K. The high-speed hub must detect a valid Chirp K after 2.5 s following its assertion. Note that if no Chirp K is detected by the hub, it completes the full-speed RESET and stays in fullspeed signaling mode.

4.Within 100 s after Chirp K from the device ends, the hub must return an alternating sequence of Chirp Ks and Chirp Js. This sequence has the following characteristics:

-no bus idles are allowed during this sequence.

-must end within 500 s and no later than 100 s prior to the end of RESET.

-each Chirp K and J is >40 s and <60 s in duration.

-RESET continues after the chirp sequence ends.

5.Once RESET time ends, the hub continues to drive SE0 via its full-speed drivers.

6.After the device detects six chirps (3 KJ pairs), it must transition to highspeed operation within 500 s. This transition requires:

-disconnecting the pull-up resistor from D+.

-enabling the high-speed terminations.

-entering the high-speed default state.

Note that the high-speed device must detect a valid chirp sequence within 1ms to 2.5ms after ending its own chirp. If no chirp sequence is detected, the high-speed device continues to operate at full speed.

Upon completion of the chirp sequence both the hub port interface and device interface will have transitioned to their high-speed signaling mode of operation.

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