Rev. 3.0, 03/01, page 328 of 390
HcRhDescriptorA
This register is only reset by a power-on reset (PCIRST#). It is written during system initialization
to configure the Root Hub. These bit should not be written during normal operation.
Table 18.41 HcRhDescriptorA Register
Register: HcRhDescriptorA
Offset: 48-4B
Bits
Reset
R/W
Description
31 - 24
01h
R/W
PowerOnToPowerGoodTime
USB Host Controller power switching is effective within 2 ms. The field
value is represented as the number of 2 ms intervals.
Only bits [25:24] are implemented as R/W. The remaining bits are read
only as ‘0’. It is not expected that these bits be written to anything other
than 1h, but limited adjustment is provided. This field should be written
to support the system implementation. This field should always be
written to a non-zero value.
23 - 13
0h
-
Reserved. Read/Write 0's
12
0
R/W
NoOverCurrentProtection
USB Host Controller implements global over-current reporting
0 = Over-current status is reported
1 = Over-current status is not reported
This bit should be written to support the external system port over-
current implementation.
11
0
R/W
OverCurrentProtectionMode
USB Host Controller implements global over-current reporting
0 = Global Over-Current
1 = Individual Over-Current
This bit is only valid when NoOverCurrentProtection is cleared. This
bit should be written '0'.
10
0
R
DeviceType
USB Host Controller is not a compound device.
9
0
R/W
NoPowerSwitching
USB Host Controller implements global power switching.
0 = Ports are power switched.
1 = Ports are always powered on.
This bit should be written to support the external system port power
switching implementation.
8
0
R/W
PowerSwitchingMode
USB Host Controller implements a global power switching mode.
0=Global Switching
1 = Individual Switching
This bit is only valid when NoPowerSwitching is cleared. This bit
should be written '0'.
7 - 0
02h
R
NumberDownstreamPorts
USB Host Controller supports two downstream ports.
Содержание HD64465
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