
176
Agere Systems Inc.
T8302 Internet Protocol Telephone
Advanced RISC Machine (
ARM
)
Data Sheet
July 2001
13 USB Host Controller
(continued)
13.5.3 Hc Fm Number Register
The
Hc Fm number register
is a 16-bit counter. It provides a timing reference among events happening in the host
controller and the host controller driver. The host controller driver may use the 16-bit value specified in this register
and generate a 32-bit frame number without requiring frequent access to the register.
Table 160
.
Hc Fm Number
Register
13.5.4 Hc Periodic Start Register
The
Hc periodic start register
has a 14-bit programmable value that determines the earliest time HC should start
processing the periodic list.
Table 161
.
Hc Periodic Start
Register
13.5.5 Hc LS Threshold
Register
The
Hc LS threshold
register
contains an 11-bit value used by the host controller to determine whether to commit
to the transfer of a maximum of 8-byte LS packet before EOF. Neither the host controller nor the host controller
driver are allowed to change this value.
Address 0xE000 703C
Bit #
Name
Bit #
31:16
RSVD
Read/Write
HCD
—
R
15:0
FN
Key
Reset
Description
HC
—
R/W
31:16
15:0
RSVD
FN
—
0
Reserved.
Frame number. This is incremented when the
Hc Fm remaining
register
is reloaded. It will be rolled over to 0H after FFFFH. When
entering the USB operational state, this will be incremented auto-
matically. The content will be written to HCCA after HC has incre-
mented the
FN
at each frame boundary and sent a SOF, but before
HC reads the first ED in that frame. After writing to HCCA, HC will
set the start of frame in the
Hc interrupt status register
.
Address 0xE000 7040
Bit #
Name
Bit #
31:14
RSVD
Read/Write
HCD
—
R/W
13:0
PS
Key
Reset
Description
HC
—
R
31:14
13:0
RSVD
PS
—
0h
Reserved.
Periodic start. After a hardware reset, this field is cleared. This is
then set by HCD during the HC initialization. The value is calculated
roughly as 10% off from the
Hc Fm interval register
. A typical
value will be 3E67h. When the
Hc Fm remaining register
reaches
the value specified, processing of the periodic lists will have priority
over control/bulk processing. HC will therefore start processing the
interrupt list after completing the current control or bulk transaction
that is in progress.