Rev. 3.0, 03/01, page 290 of 390
ResumeDetected Event
A resume detected event occurs when the Root Hub detects resume signaling on the USB bus. The
Host Controller will set the ResumeDetected bit when resume signaling is detected.
A ResumeDetected interrupt is only possible in the U
SB
S
USPEND
state. A resume event can be
either an upstream resume signal or a connect/disconnect detection at a port. The connect/
disconnect resume event is enabled by the RemoteWakeupEnable in the HcRhStatus register. If a
port is either in the progress of selectively resuming or has completed the selective resume and set
PortSuspendStatusChange when the Root Hub enters the U
SB
S
USPEND
state, the port resume is
cleared and the hub resume, ResumeDetected, is generated.
The ResumeDetected event may occur while the system clock is disabled. The interrupt processor
will generate an interrupt for an enabled ResumeDetected event. The interrupt will remain active
until the clock is enabled and the ResumeDetected bit in the interrupt status register is cleared.
UnrecoverableError Event
This implementation does not support generation of an Unrecoverable Error event.
FrameNumberOverflow Event
When the MSB (bit 15) of the FrameNumber field of HcFmNumber changes value, the
FrameNumberOverflow bit is set by the Host Controller following the next HccaFrameNumber
update. The event occurs on both the ‘1’ to ‘0’ or the ‘0’ to ‘1’ transition. This event allows the
Host Controller Driver to perform any necessary manipulation of its software based frame number
to ensure that number is correct.
RootHubStatusChange Event
The Host Controller sets the RootHubStatusChange bit whenever there is a change to any bit in
HcRhStatus or HcRhPortStatus. Any changes in these registers define a change in status that must
be communicated to the Host Controller Driver. Since OpenHCI provides a register-level interface
to the Root Hub, the need for Root Hub Transfer Descriptors is eliminated. This provides for a
more efficient Root Hub interface, but does not provide the Host Controller Driver a good
mechanism for polling the Root Hub on a periodic basis. To compensate for the lack of a good
polling mechanism, the Host Controller delivers an interrupt on every Root Hub status change.
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