NEC Network Controller uPD98502 - Manual (Page 364)

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 V R 4120A of its having received
Suspend or Resume signaling from a Host PC. When the V
R
4120A receives a Suspend or a Resume, it must perform
the appropriate processing.
Also, for those instances when the port to which the µPD98502 is connected is in the Suspend status (the
µPD98502 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
µPD98502 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
V R 4120A
U S B
C ontroller
S tarts suspend.
S tops the
transaction on U S B
3 m s
If U S B has no
activity for m ore
than 3 m s, the
device connected
to U S B transits in
S uspend state.
S ets U S P D
bit (B it16) in U S B
G eneral S tatus
R egister 2 to
a '1', issues the
interruption to
V R 4120A .
R eceives U S B
in terrup tio n ,re ad s
status register.
R ecognizes U S B
becam e suspend
state
H ost P C
(2) T ransits in
suspend state,
because U S B has
no activity for
m ore than 3 m s.
(3)
(4)
(2)
(1)
µ P D 98502
(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 V
R
4120A if interrupt is not masked.
(4) The V
R
4120A 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.