HS_USB2.0 host
RM0082
456/844
Doc ID 018672 Rev 1
22.6.47 HcRhDescriptorB
register
The HcRhDescriptorB register is the second register of two describing the characteristics of
the Root Hub. These fields are written during initialization to correspond with the system
implementation. Reset values are implementation-specific.
[08]
PSM
IS
R/W
R
PowerSwitchingMode
This bit is used to specify how the power switching of the
Root Hub ports is controlled. It is implementation-specific.
This field is only valid if the NoPowerSwitching field is
cleared.
0: all ports are powered at the same time.
1: each port is powered individually. This mode allows port
power to be controlled by either the global switch or
perport switching. If the PortPowerControlMask bit is set,
the port responds only to port power commands
(Set/ClearPortPower). If the port mask is cleared, then the
port is controlled only by the global power switch
(Set/ClearGlobalPower).
[07:00]
NDP
IS
R/W
R
NumberDownstreamPorts
These bits specify the number of downstream ports
supported by the Root Hub. It is implementation-specific.
The minimum number of ports is 1. The maximum number
of ports supported by OpenHCI is 15.
Table 384.
HcRhDescriptorA register bit assignments (continued)
Bits
Name
Reset
Read/Write
Description
HCD
HC