USB Host Controller
1549
SPNU503C – March 2018
Copyright © 2018, Texas Instruments Incorporated
Universal Serial Bus (USB)
29.2.4.18 HC Low-Speed Threshold Register (HCLSTHRESHOLD)
The HC low-speed threshold register defines the latest time in a frame that the USB host controller can
begin a low-speed packet.
Figure 29-18. HC Low-Speed Threshold Register (HCLSTHRESHOLD) [address = FCF78B44h]
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 at reset
Table 29-20. HC Low-Speed Threshold Register (HCLSTHRESHOLD) Bit 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 USB host
controller cannot start an 8-byte low-speed packet. The USB host controller only begins a low-
speed transaction if the frame remaining field 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.
29.2.4.19 HC Root Hub A Register (HCRHDESCRIPTORA)
The HC root hub A register defines several aspects of the USB host controller root hub functionality.
Figure 29-19. HC Root Hub A Register (HCRHDESCRIPTORA) [address = FCF78B48h]
31
24
23
16
POTPG
Reserved
R/W-2h
R-0
15
13
12
11
10
9
8
7
0
Reserved
NOCP
OCPM
DT
NPS
PSM
NDP
R/W-0
R/W-1
R/W-0
R-0
R/W-1
R/W-0
R-2h
LEGEND: R/W = Read/Write; R = Read only; -
n
= value at reset
Table 29-21. HC Root Hub A Register (HCRHDESCRIPTORA) Field Descriptions
Bit
Field
Value
Description
31-24
POTPG
0-FFh
Power-on to power-good time
This field defines the minimum amount of time (2 ms × POTPG) between the USB host controller
turning on power to a downstream port and when the USB host can access the downstream device.
The default value is 0x2, so that the time is 4 ms.
This field has no effect on USB host controller operation. After turning on power to a port, the USB
host controller driver must delay the amount of time implied by POTPG before attempting to reset
an attached downstream device.
The required amount of time is system implementation-specific and must be calculated based on
the amount of time the VBUS supply takes to provide valid VBUS to a worst-case downstream USB
function controller.
The implementation-specific value must be computed and then written to this register before the
USB host controller driver is initialized.
23-13
Reserved
0
Reserved