CHAPTER 6 USB CONTROLLER
364 Preliminary User’s Manual S15543EJ1V0UM
6.7 Power Management
USB Controller has a built in feature that allows it to use interrupts to inform the VR4120A of its having received
Suspend or Resume signaling from a Host PC. When the VR4120A receives a Suspend or a Resume, it must perform
the appropriate processing.
Also, for those instances when the port to which the
µ
PD98502 is connected is in the Suspend status (the
µ
PD98502 is in the Suspend status), USB Controller has a function for issuing Remote Wake Up signaling to switch
the Suspend status to Resume.
As a result, even if the
µ
PD98502 is in the Suspend status, data that arrives from the line (ADSL) is not discarded
but can be passed to a Host PC.
The following sections explain each of the sequences.
6.7.1 Suspend
The Suspend sequence is as shown below.
Figure 6-27. Suspend Sequence
VR4120A USB
Controller
Starts suspend.
Stops the
transaction on USB
3 ms
If USB has no
activity for more
than 3 ms, the
device connected
to USB trans its in
Suspend state.
Sets USPD
bit (Bit16) in USB
General Status
Register 2 to
a '1', issues the
interruption to
VR4120A.
Receives USB
interruption,reads
status register.
Recognizes USB
became suspend
state
Host PC
(2)Transits in
suspend state,
because USB has
no activity for
more than 3 ms.
(3)
(4)
(2)
(1)
µ
PD98502
(1) The host places the USB in the Suspend status. Traffic stops flowing through the USB.
(2) After 3 ms there is no traffic through the USB. Therefore, all of the devices connected to the USB shift to the
Suspend status. In the same way, USB Controller also enters the Suspend status. During DMA transfer is
being performed, however, USB Controller does not enter the Suspend status until after the completion of
DMA transfer.
(3) USB Controller sets the USPD bit (Bit16) of the USB General Status Register 2 (Address: 1000_1018H) to a
‘1’, then issues an interrupt to the VR4120A if interrupt is not masked.
(4) The VR4120A receives the interrupt from USB Controller, reads the USB General Status Register 2 and, as a
result, determines that the USB is in the Suspend status.