USB Host Controller Registers
14-25
Universal Serial Bus Host
The HC root hub A register defines several aspects of the USB host controller
root hub functionality.
Table 14–20. HC Root Hub A Register (HcRhDescriptorA)
Bit
Name
Value
Description
Type
Reset
Value
31–24
POTPG
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.
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 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.
Because OMAP5910 does not provide a direct control
from the USB host controller to switch VBUS on and
off, this value must take into account any delays
caused by other methods of controlling VBUS
externally.
R/W
0xA
23–13
Reserved
Reserved
12
NOCP
No overcurrent protection
When 1, this bit indicates that the USB host controller
does not implement overcurrent protection inputs.
OMAP5910 does not provide signals to allow
connection of external overcurrent indication signals to
the USB host controller, so this bit defaults to 1.
R/W
1
11
OCPM
Overcurrent protection mode
OMAP5910 does not provide overcurrent protection
input signals, so this bit has no effect.
R/W
0