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UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
564 of 1269
NXP Semiconductors
UM10503
Chapter 23: LPC43xx USB0 Host/Device/OTG controller
•
After a Port Change Detect, the device has reached the default state and the DCD
can read the PORTSC1 to determine if the device is operating in FS or HS mode. At
this time, the device controller has reached normal operating mode and DCD can
begin enumeration according to the
USB2.0 specification Chapter 9 - Device
Framework
.
Remark:
The device DCD may use the FS/HS mode information to determine the
bandwidth mode of the device.
In some applications, it may not be possible to enable one or more pipes while in FS
mode. Beyond the data rate issue, there is no difference in DCD operation between FS
and HS modes.
23.10.4 Suspend/resume
23.10.4.1 Suspend
In order to conserve power, USB devices automatically enter the Suspended state when
the device has observed no bus traffic for a specified period. When suspended, the USB
device maintains any internal status, including its address and configuration. Attached
devices must be prepared to suspend any time they are in the Default, Address, or
Configured state. Bus activity may cease due to the host entering a suspend mode of its
own. In addition, a USB device shall also enter the suspended state when the hub port it is
attached to is disabled.
A USB device exits suspend mode when there is bus activity. A USB device may also
request the host to exit suspend mode or selective suspend by using electrical signaling to
indicate remote wake-up. The ability of a device to signal remote wake-up is optional. If
the USB device is capable of remote wake-up signaling, the device must support the
ability of the host to enable and disable this capability. When the device is reset, remote
wake-up signaling must be disabled.
23.10.4.1.1
Operational model
The device controller moves into the Suspended state when suspend signaling is
detected or activity is missing on the upstream port for more than a specific period. After
the device controller enters the Suspended state, the DCD is notified by an interrupt
(assuming DC Suspend Interrupt is enabled). When the DCSuspend bit in the PORTSC1
is set to a ‘1’, the device controller is suspended.
DCD response when the device controller is suspended is application specific and may
involve switching to low power operation. Information on the bus power limits in the
Suspended state can be found in
USB 2.0 specification
.
23.10.4.2 Resume
If the device controller is suspended, its operation is resumed when any non-idle signaling
is received on its upstream facing port. In addition, the device can signal the system to
resume operation by forcing resume signaling to the upstream port. Resume signaling is
sent upstream by writing a ‘1’ to the Resume bit in the in the PORTSC1 while the device is
in the Suspended state. Sending resume signal to an upstream port should cause the host
to issue resume signaling and bring the suspended bus segment (one or more devices)
back to the active condition.