HS_USB2.0 host
RM0082
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Doc ID 018672 Rev 1
Table 379.
HcFmInterval register bit assignments
22.6.41 HcFmRemaining
register
The HcFmRemaining register is a 14 bit down counter showing the bit time remaining in the
current Frame.
Bits
Name
Reset
Read/Write
Description
HCD
HC
[31]
FIT
0b
R/W‘
R
FrameIntervalToggle
HCD toggles this bit whenever it loads a new value to
FrameInterval.
[30:16]
FSMPS TBD
R/W
R
FSLargestDataPacket
This field specifies a value which is loaded into the
Largest Data Packet Counter at the beginning of each
frame. The counter value represents the largest amount
of data in bits which can be sent or received by the HC in
a single transaction at any given time without causing
scheduling overrun. The field value is calculated by the
HCD.
[15:14]
Reserved
[13:00]
FI
2EDFh R/W
R
FrameInterval
This specifies the interval between two consecutive
SOFs in bit times. The nominal value is set to be 11,999.
HCD should store the current value of this field before
resetting HC. By setting the HostControllerReset field of
HcCommandStatus as this will cause the HC to reset this
field to its nominal value. HCD may choose to restore the
stored value upon the completion of the Reset sequence.
Table 380.
HcFmRemaining register bit assignments
Bits
Name
Reset
Read/Write
Description
HCD
HC
[31]
FRT
0b
R
R/W
FrameRemainingToggle
This bit is loaded from the FrameIntervalToggle field of
HcFmInterval whenever FrameRemaining reaches 0. This
bit is used by HCD for the synchronization between
FrameInterval and FrameRemaining.
[30:14]
Reserved
[13:00]
FR
0h
R
R/W
FrameRemaining
This counter is decremented at each bit time. When it
reaches zero, it is reset by loading the FrameInterval
value specified in HcFmInterval at the next bit time
boundary. When entering the USBOPERATIONAL state,
HC re-loads the content with the FrameInterval of
HcFmInterval and uses the updated value from the next
SOF.