USB Host Controller Registers
14-22
The HC head done register defines the local bus virtual address of the current
head of the done TD queue.
Table 14–14. HC Head Done Register (HcDoneHead)
Bit
Name
Description
Type
Reset
Value
31–4
DH
Local bus virtual address of the last TD that was added to
the done queue.
This field represents bits 31:4 of the local bus virtual
address of the top TD on the done TD queue. TDs are
assumed to begin at 16-byte-aligned address, so bits 3:0 of
this pointer are assumed to be 0. See See Section 14.6.1,
Local Bus Addressing, for the restrictions on local bus
virtual addresses.
A value of 0x00000000 indicates that there are no TDs on
the done queue.
This register is automatically updated by the USB host
controller.
R
0x0000000
3 – 0
Reserved
Reserved
R
0x0
The HC frame interval register defines the number of 12-MHz clock pulses in
each USB frame.
Table 14–15. HC Frame Interval Register (HcFmInterval)
Bit
Name
Description
Type
Reset
Value
31
FIT
Frame interval toggle
The host controller driver must toggle this bit any time it
changes the frame interval field.
R/W
0
30–16
FSMPS
Largest data packet
Largest data packet size allowed for full speed packets, in bit
times.
R/W
0
15–14
Reserved
Reserved
13–0
FI
Frame interval
Number of 12-MHz clocks in the USB frame. Nominally, this
is set to 11,999, to give a 1-ms frame. The host controller
driver may make minor changes to this field to attempt to
manually synchronize with another clock source.
R/W
0x2EDF