Rev. 3.0, 03/01, page 262 of 390
USB OPERATIONAL
When in the U
SB
O
PERATIONAL
state, the Host Controller may process lists and will generate SOF
Tokens. The U
SB
O
PERATIONAL
state may be entered from the U
SB
R
ESUME
or U
SB
R
ESET
states. It
may be exited to the U
SB
R
ESET
or U
SB
S
USPEND
states.
When transitioning from U
SB
R
ESET
or U
SB
R
ESUME
to U
SB
O
PERATIONAL
, the Host Controller is
responsible for terminating the USB reset or resume signaling as defined in the USB Specification
prior to sending a token.
A transition to the U
SB
O
PERATIONAL
state affects the frame management registers of the Host
Controller. Simultaneously with the Host Controller state transition to U
SB
O
PERATIONAL
, the
FrameRemaining field of HcFmRemaining is loaded with the value of the FrameInterval field in
HcFmInterval. There is no SOF Token sent at this initial load of the FrameRemaining field. The
first SOF Token sent after entering the U
SB
O
PERATIONAL
state is sent following next frame
boundary when FrameRemaining transitions from 0 to FrameInterval. The FrameNumber field
of HcFmNumber is incremented on a state transition to U
SB
O
PERATIONAL
.
USB RESET
When in the U
SB
R
ESET
state, the Host Controller forces reset signaling on the bus. The Host
Controller list processing and SOF Token generation are disabled while in U
SB
R
ESET
. In addition,
the FrameNumber field of HcFmNumber does not increment while the Host Controller is in the
U
SB
R
ESET
state. The U
SB
R
ESET
state can be entered from any state at any time. The Host
Controller defaults to the U
SB
R
ESET
state following a hardware reset. The Host Controller Driver
is responsible for satisfying USB Reset signaling timing defined by the USB Specification.
USB SUSPEND
The U
SB
S
USPEND
state defines the USB Suspend state. The Host Controller list processing and
SOF Token generation are disabled. However, the Host Controller remote wakeup logic must
monitor USB wakeup activity. The FrameNumber field of HcFmNumber does not increment
while the Host Controller is in the U
SB
S
USPEND
state.
U
SB
S
USPEND
is entered following a software reset or from the U
SB
O
PERATIONAL
state on
command from the Host Controller Driver. While in U
SB
S
USPEND
, the Host Controller may force a
transition to the U
SB
R
ESUME
state due to a remote wakeup condition. This transition may conflict
with the Host Controller Driver initiating a transition to the U
SB
R
ESET
state. If this situation
occurs, the HCD-initiated transition to U
SB
R
ESET
has priority. The Host Controller Driver must
wait 5 ms after transitioning to U
SB
S
USPEND
before transitioning to the U
SB
R
ESUME
state.
Likewise, the Root Hub must wait 5 ms after the Host Controller enters U
SB
S
USPEND
before
generating a local wakeup event and forcing a transition to U
SB
R
ESUME
. Following a software
reset, the Host Controller Driver may cause a transition to U
SB
O
PERATIONAL
if the transition
occurs no more than 1 ms from the transition into U
SB
S
USPEND
. If the 1-ms period is violated, it is
possible that devices on the bus will go into Suspend.
Содержание HD64465
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