RM0082
HS_USB2.0 host
Doc ID 018672 Rev 1
453/844
22.6.42 HcFmNumber
register
The HcFmNumber 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 381.
HcFmNumber register bit assignments
22.6.43 HcPeriodicStart
register
The HcPeriodicStart register has a 14 bit programmable value which determines when is the
earliest time HC should start processing the periodic list.
Table 382.
HcPeriodicStart register bit assignments
22.6.44 HcLSThreshold
register
The HcLSThreshold 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.
Bits
Name
Reset
Read/Write
Description
HCD
HC
[31:16]
Reserved
[15:00]
FN
0h
R
R/W
FrameNumber
This is incremented when HcFmRemaining is re-loaded. It
will be rolled over to 0h after ffffh. When entering the
USBOPERATIONAL state, this will be incremented
automatically. The content will be written to HCCA after
HC has incremented the FrameNumber 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
StartofFrame in HcInterruptStatus.
Bits
Name
Reset
Read/Write
Description
HCD
HC
[31:14]
Reserved
[13:00]
PS
0h
R/W
R
PeriodicStart
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 HcFmInterval. A
typical value will be 3E67h. When HcFmRemaining
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.