
Principles of Operation
67
September 2005
SCPS110
3.8.9 PCI Power Management
3.8.9.1
CardBus (Function 0) Power Management
The PCI Bus Power Management Interface Specification for PCI to CardBus Bridges establishes the
infrastructure required to let the operating system control the power of PCI functions. This is accomplished
by defining a standard PCI interface and operations to manage the power of PCI functions on the bus. The
PCI bus and the PCI functions can be assigned one of seven power-management states, resulting in varying
levels of power savings.
The seven power-management states of PCI functions are:
D0-uninitialized Before controller configuration, controller not fully functional
D0-active Fully functional state
D1 Low-power state
D2 Low-power state
D3hot Low-power state. Transition state before D3cold
D3cold PME signal-generation capable. Main power is removed and VAUX is available.
D3off No power and completely nonfunctional
NOTE 1: In the D0-uninitialized state, the PCIxx12 controller does not generate PME and/or interrupts. When bits 0 (IO_EN) and 1 (MEM_EN)
of the command register (PCI offset 04h, see Section 4.4) are both set, the PCIxx12 controller switches the state to D0-active. Transition
from D3cold to the D0-uninitialized state happens at the deassertion of PRST. The assertion of GRST forces the controller to the
D0-uninitialized state immediately.
NOTE 2: The PWR_STATE bits (bits 10) of the power-management control/status register (PCI offset A4h, see Section 4.43) only code for four
power states, D0, D1, D2, and D3hot. The differences between the three D3 states is invisible to the software because the controller
is not accessible in the D3cold or D3off state.
Similarly, bus power states of the PCI bus are B0B3. The bus power states B0B3 are derived from the device
power state of the originating bridge device.
For the operating system (OS) to manage the controller power states on the PCI bus, the PCI function must
support four power-management operations. These operations are:
Capabilities reporting
Power status reporting
Setting the power state
System wake-up
The OS identifies the capabilities of the PCI function by traversing the new capabilities list. The presence of
capabilities in addition to the standard PCI capabilities is indicated by a 1b in bit 4 (CAPLIST) of the status
register (PCI offset 06h, see Section 4.5).
The capabilities pointer provides access to the first item in the linked list of capabilities. For the PCIxx12
controller, a CardBus bridge with PCI configuration space header type 2, the capabilities pointer is mapped
to an offset of 14h. The first byte of each capability register block is required to be a unique ID of that capability.
PCI power management has been assigned an ID of 01h. The next byte is a pointer to the next pointer item
in the list of capabilities. If there are no more items in the list, then the next item pointer must be set to 0. The
registers following the next item pointer are specific to the capability of the function. The PCI
power-management capability implements the register block outlined in Table 315.
Table 315. Power-Management Registers
REGISTER NAME
OFFSET
Power-management capabilities
Next item pointer
Capability ID
A0h
Data
Power-management control/status register bridge support extensions
Power-management control/status (CSR)
A4h
The power-management capabilities register (PCI offset A2h, see Section 4.42) provides information on the
capabilities of the function related to power management. The power-management control/status register
(PCI offset A4h, see Section 4.43) enables control of power-management states and enables/monitors
power-management events. The data register is an optional register that can provide dynamic data.