Universal Serial Bus OHCI Host Controller User's Guide

3.17 HC Periodic Start Register (HCPERIODICSTART)
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The HC periodic start register (HCPERIODICSTART) defines the position within the USB frame where
endpoint descriptors (EDs) on the periodic list have priority over EDs on the bulk and control lists.
HCPERIODICSTART is shown in Figure 18 and described in Table 18 .
Figure 18. HC Periodic Start Register (HCPERIODICSTART)
31 16
Reserved
R-0
15 14 13 0
Reserved PS
R-0 R/W-0
LEGEND: R/W = Read/Write; R = Read only; - n = value after reset
Table 18. HC Periodic Start Register (HCPERIODICSTART) Field Descriptions
Bit Field Value Description
31-14 Reserved 0 Reserved
13-0 PS 0-3FFFh Periodic start. The host controller driver must program this value to be about 10% less than the
frame interval (FI) value in the HC frame interval register (HCFMINTERVAL), so that control and
bulk EDs have priority for the first 10% of the frame; then periodic EDs have priority for the
remaining 90% of the frame.
SPRUFM8 – September 2008 Universal Serial Bus OHCI Host Controller 25
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