USS-820FD
USB Device Controller
Data Sheet, Rev. 1
August 2004
The register bits that are only updated by firmware, but
reside in registers with shared bits and must therefore
be updated only while PEND is set, are shown in
Table 11. Register Bits Only Updated While PEND
is Set
Register
RXSTAT
EPCON
SOFH
SSR
Bit(s)
RXSEQ
All bits except RXSTL
SOFIE, SOFODIS
SUSPPO, SUSPDIS, RESUME,
SUSPEND
Register Interface
(continued)
In this case, the SBI/SBI1 bit will be set even though
there is no corresponding data set present in the
receive FIFO. Therefore, firmware must be prepared to
service a receive done interrupt where no data sets are
present in the indicated FIFO.
standard copies of the shared register bits when firm-
ware resets the PEND register bit
.
Table 10. Shared Register Update Values When
Firmware Resets PEND
Register
SBI
Bit(s)
All bits
Update Value
Set to 1 if standard copy = 1 or
pended copy = 1.
SBI1
All bits Set to 1 if standard copy = 1 or
pended copy = 1.
RXSTAT RXSETUP Loaded with pended copy if
USB action updated RXSETUP
while PEND was set.
RXSTAT EDOVW Set to 1 if standard copy = 1 or
pended copy = 1.
EPCON RXSTL Set to 1 if standard copy = 1 or
pended copy = 1.
SOFH
ASOF Set to 1 if standard copy = 1 or
pended copy = 1.
SOFH
TS
Loaded with pended copy if
USB SOF was received while
PEND was set.
SOFL
All bits Loaded with pended copy if
USB SOF was received while
PEND was set.
SSR
RESET Set to 1 if standard copy = 1 or
pended copy = 1.
Firmware should attempt to minimize the period during
which PEND is set in order to minimize the distortion of
the detection of hardware events.
Register Reads with Side Effects
In general, USS-820FD register reads do not have side
effects—they do not cause any device state to change.
The following are exceptions to this rule:
■
RXDAT reads cause the internal RX FIFO read
pointer to change and possibly cause the
RXFLG.RXURF register bit to set.
RXCNTH/RXCNTL reads while RXFLG.RXFIF = 00
cause the RXFLG.RXURF register bit to set.
LOCK reads restart the register unlock sequence
after suspend (described in
Special Action Required
by USS-820/USS-825 After Suspend—AP97-
058CMPR-04).
Any register reads during a register unlock sequence
after suspend, other than the LOCK register, cause
the unlock sequence to fail and require the sequence
to be restarted.
■
■
■
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Agere Systems Inc.
AGERE [ AGERE SYSTEMS ]
