UM10503
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User manual
Rev. 1.3 — 6 July 2012
583 of 1269
NXP Semiconductors
UM10503
Chapter 23: LPC43xx USB0 Host/Device/OTG controller
2. If the host puts resume signaling on the bus, it will clear the Suspend bit and generate
a port change interrupt when the resume is finished.
Remark:
The Suspend interrupt is generated by the USB block whenever it detects that
the bus is idle for more than 3 ms. However, during the enumeration process some hosts
wait longer than 3 ms after issuing reset and before transmitting any tokens on bus.
Hence software should implement a debounce logic for suspend interrupt handling to
detect a true suspend command issued by host.
23.11.3 Host power states
From an operational state when a host gets a low power request, it must set the suspend
bit in the port controller. This will put an idle on the bus, block all traffic through the port,
and turn off the transceiver clock. There are two ways for a host controller to get out of the
Suspended state. If it has enabled remote wake-up, a K-state on the bus will turn on the
transceiver clock and generate an interrupt. The software will then have to wait 20 ms for
the resume to complete and the port to go back to an active state. Alternatively an
Fig 61. Host/OTG power state diagram
operational
disconnect
SW sets
Suspend bit
user-defined
wakeup
disconnect
Suspend
Suspend
user-defined
wakeup
Lock power states
(clock may be suspended)
Low-power
request
all devices
disconnected
signal
Suspend
wait for
3 ms
K-state
on bus
Wait
Resume
Resume or
Reset
connect
interrupt