The USB 2.0 port indicators are also supported directly by TetraHub. As per the specification, each downstream port of the hub
supports an optional status indicator. The presence of indicators for downstream facing ports is specified by bit 7 of the
wHubCharacteristics field of the hub class descriptor. The default TeraHub descriptor specifies that port indicators are supported
(wHubCharacteristics, bit 7 is set). If port indicators are not included in the hub, this should be disabled by the EEPROM.
Each port indicator is strategically located directly on the opposite edge of the port which it is associated with. The indicator
provides two colors: green and amber. This is implemented as two separate LEDs, one amber and the other green. A combination
of hardware and software control is used to inform the user of the current status of the port or the device attached to the port and
to guide the user through problem resolution. Colors and blinking are used to provide information to the user. The significance of
the color of the LED depend on the operational mode of the TetraHub. There are two modes of operation for the TetraHub port
indicators: automatic and manual.
On power-up the TeraHub defaults to Automatic Mode, where the color of the Port Indicator (Green, Amber, Off) indicates the
functional status of the TetraHub port. In Automatic Mode, TetraHub will turn on the green LED whenever the port is enabled and
the amber LED when it has had an overcurrent condition detected. The color of the port indicator is set by the port state machine.
Blinking of the LEDs is not supported in Automatic Mode.
below identifies the mapping of color to port state in Automatic
Table 4-1. Automatic Port State to Port Indicator Color Mapping
Downstream Facing Hub Port State
Off or Amber if due to an
Disconnected, Disabled, Not
Configured, Resetting, Testing
Off or Amber if due to an
SendEOR, Restart_E /S
In manual mode, the indicators are under the control of the host, which can turn on one of the LEDs, or leave them off. This is
done by a system software USB Hub class request. Blinking of the LEDs is supported in Manual Mode. The port indicators allow
the user to intervene on any error detection. For example, when babble is detected on plugging in a defective device, or on
occurrence of an overcurrent condition, the port indicators corresponding to the downstream port will blink green or only light the
amber LED, respectively.
below displays the color definition of the indicators when TetraHub is in Manual Mode.
Table 4-2. Port Indicator Color Definitions in Manual Mode
Information presented in
is from USB 2.0 specification Tables 11-6 and 11-7, respectively.
Document #: 38-08019 Rev. *E
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