OXCB950 datasheet(23/68 Pages) ETC

23 / 68 page

Data Sheet Revision 1.1

Page 23

OXCB950

OXFORD SEMICONDUCTOR LTD.

6.6.3

Cardbus Power management

For cardbus mode, the cardbus status registers as given by

the tuple CISTPL_CONFIG_CB and located at the memory

base address register BAR4, are disabled (bypassed) by

default. This results in the power management behaviour

for the device in cardbus mode to be identical to the power

management behaviour for the device in the pci mode, with

the exception that the power management event (the

wakeup request) is available on the CSYSCHG pin for

cardbus modes and the PME# pin for pci modes.

The default setting means that all ‘powerdown’ and

‘wakeup’ requests, in the cardbus mode, have not been

conditioned by the 4 sets of registers making up the

cardbus status registers. For those applications that require

the cardbus status registers to be enabled, then the power

management logic for cardbus mode incurs the following

controls.

Since all powerdown requests are interrupt requests, then

powerdown requests on the device’s interrupt pin (CINT#)

will be controlled according to the INTR fields of the

cardbus status registers. That is, a powerdown request will

be asserted only if the INTR field in the Function Event

Mask Register has been set and the corresponding field in

the Function Event Register has detected a valid (internal)

power down request. Similarly, the wakeup (power

management events) are controlled by the GWAKE/WKUP

fields in the cardbus status registers. A ‘wakeup’ event for

cardbus applications will only be invoked if the

GWAKE/WKUP fields in the Function Event Mask Register

have been enabled and the GWAKE field in the Function

Event Register has detected a ‘wakeup’ request. Note that

these controls are on top of the controls for ‘powerdown’

and ‘wakeup’ requests as given in the local configuration

registers.

Specifically for the generation of ‘wake-up’ events, the PC

Card Standard notes that in an ACPI operating system,

there is no cardbus device driver and so, in order to

support power management events the PME_EN bit in the

PCI configuration region must support generating a

CSYSCHG signal for a cardbus card. PME_en must make

the cardbus card power management functionality act as if

the cardbus card were a standard PCI device.

To achieve this effect when the cardbus status registers

are enabled, when the operating system sets the PME_En

bit true (in the PCI power management register block) this

action also sets true the GWAKE bit (bit4) and the WKUP

bit (bit14) fields in the Cardbus Function Event Mask

allow the assertion of the CSYSCHG line. Setting the

PME_En bit false, also clears the GWAKE and WKUP bits

in the Function Event Mask Register to deassert or inhibit

the power management on the CSYSCHG line.

Once the PME_En bit is set, the function targets the

GWAKE bit in the Function Event Register as the function’s

general wakeup event. When enabled (PME_En true) any

wakeup events are latched into the PME_status and the

cardbus card’s GWAKE bit in the Function Event register.

Clearing the GWAKE/WKUP fields in the Function Event

Mask Register, to disable wakeup events on the CSYCHG

pin, does not clear the PME_En bit in the PCI power

management

PME_status bit of the PCI power management register

block will clear the GWAKE bit in the Function Event

GWAKE bit in the Function Event register, by writing a ‘1’,

clears the PME_status bit in the PMCSR register.

These actions are sumarised below (taken from table 6-2 of the PC card standard)

ACPI Operating System

Cardbus PCI

Configuration Space

Function Event Mask

Function Event

Cardbus pin

Cardbus PCI

configuration Space

PME_En

GWAKE / WKUP

GWAKE

CSYSCHG

PME_status

Default 0

Default 0 / Default 0

Defualt 0

Default 0

Written 1

Follows PME_en

1 / 1

1(detected wakeup

event)

Latches wakeup

(CSYSCHG) event

Written 0

Follows PME_en

Don’t Care

Don’t care/ Don’t care

Non-ACPI Operating System

No effect

Per cardbus electrical sepcification

No effect

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