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Registers
1598
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Universal Serial Bus OHCI Host Controller
33.3.17 HC Periodic Start Register (HCPERIODICSTART)
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
and described in
Figure 33-18. 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 33-18. 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.
33.3.18 HC Low-Speed Threshold Register (HCLSTHRESHOLD)
The HC low-speed threshold register (HCLSTHRESHOLD) defines the latest time in a frame that the
USB1.1 host controller can begin a low-speed packet. HCLSTHRESHOLD is shown in
and
described in
Figure 33-19. HC Low-Speed Threshold Register (HCLSTHRESHOLD)
31
16
Reserved
R-0
15
14
13
0
Reserved
LST
R-0
R/W-628h
LEGEND: R/W = Read/Write; R = Read only; -
n
= value after reset
Table 33-19. HC Low-Speed Threshold Register (HCLSTHRESHOLD) Field Descriptions
Bit
Field
Value
Description
31-14
Reserved
0
Reserved
13-0
LST
0-3FFFh
Low-speed threshold. This field defines the number of full-speed bit times in the frame after which
the USB1.1 host controller cannot start an 8-byte low-speed packet. The USB1.1 host controller
only begins a low-speed transaction if the frame remaining (FR) value in the HC frame remaining
register (HCFMREMAINING) is greater than the low-speed threshold.
The host controller driver must set this field to a value that ensures that an 8-byte low-speed TD
completes before the end of the frame. When set, the host controller driver must not change the
value.