4-8
AIC-6915 Ethernet LAN Controller Programmer’s Manual
Power Management
The PCI bus power management defined four power states. D0 indicates the “On” state,
D3 indicates the “Off” state, and D1 and D2 represent power managed states. In the
AIC-6915, three states are supported. D0 and D3 are required states and D2 is an optional
state. Table 4-1 shows the states supported by the AIC-6915.
The assertion of
RST_
on the PCI bus always returns the PCI function to the D0
uninitialized power-on default state. Removing Vcc always transitions the function to the
D3 state. All other function power state changes are made by software through the
PMCSR
register.
When a function is not in the D0 state, the value of the Bus Master, Memory Space and
I/O Space bits in the PCI Command register are ignored, along with all Memory and I/O
accesses on the PCI bus. In the D1, D2, and D3 states, only PCI configuration space can be
accessed. All the other functional blocks are stopped, including the PCI master sub-
module and the BAC module.
For the device to start another transaction other than a configuration access, software
must return that device to the D0 state. This is accomplished by setting the Powerstate bits
in the PMCSR register to the D0 state, or by a wakeup event that is initiated by the Receive
module. When the PCI module receives any transfer request from the Receive module, it
generates a PME_ (Power Management Event) interrupt. Software then checks the power
management status registers and sets the PowerState to D0 and activates the full power
PCI bus access. PME_ can be enabled by setting PME_Support field in the PMC (Power
Management Capabilities) register.
When the
P
OWER
S
TATE
bits in
PMCSR
are being changed, the PCI module sends a state
change request to all other modules to make sure there are no current of pending
transfers. The power state can be changed only after acknowledgment is received from all
modules.
Table 4-1. Power Management States
Device
States
Function Context
Power
Supported
Action to
Function
Supported
Actions from
Function
Implementation in
PCI Module
D0
All context is
retained
Full power
Any PCI
transaction
Any PCI
transaction or
interrupt
Regular power and
clocks
D2
All PCI
configuration
registers and
Receive module
are retained
Lower power
than D0
PCI
Configuration
Access
Wakeup
event
All clocks stop
other than target
module and
Receive module.
Target abort if not
config cycle
D3
All PCI
configuration
registers are
retained
Lower power
than any other
state
PCI
Configuration
Access
No action
All clocks stop
other than target
module. target
abort if not config
cycle
