OXCB950 datasheet(22/68 Pages) ETC

22 / 68 page

Data Sheet Revision 1.1

Page 22

OXCB950

OXFORD SEMICONDUCTOR LTD.

Upon a power down interrupt, the device driver can change

the power-state of the device as required. Note that the

power-state of the device is only changed by the device

driver and at no point will the OXCB950 change its own

power state. The powerdown interrupt merely informs the

device driver that this logical function is ready for power

down. Before placing the device into the lower power

states, the driver must provide the means for the function

to generate a ‘wakeup’ (power management) event.

Whenever the device driver changes the power-state to

state D2 or D3, the device takes the following actions:

•

The internal clock to internal UART is shut down.

•

Cardbus/PCI interrupts are disabled regardless of the

values contained in the GIS registers.

•

Access to I/O or Memory BARs.

However, access to the configuration space is still enabled.

The device driver can optionally assert/de-assert any of its

selected (design dependent) MIO pins to switch-off VCC,

disable other external clocks, or activate shut-down modes.

The device can only issue a wakeup request (power

management event) if it is enabled by the PCI Power

Management Register PMCSR(8), the PME_En bit. PME#

assertion, the wakeup event for pci modes, and CSYSCHG

assertion, the wakeup event for cardbus modes, is

immediate and does not use the powerdown filter timer. It

operates even if the powerdown filter time is set to

disabled.

Like powerdown, wakeup requests can be generated by 3

sources: the internal UART and the 2 Multi_purpose MIO

pins. The means to generate wakeup events from these

sources will have been setup prior to placing the device

into the powerdown states D2 or D3.

For the case of the UART, when the device is in the

powerstate D3, only activity on the RI line (the trailing edge

of a pulse) will generate a wakeup event as long as the

PME_En bit is set. When the device is in power-state D3, a

change in the state of any modem line which is enabled by

a 16C950-specific mask bit, or a change in the state of the

serial input line if enabled by a 16C950-specific mask bit

can issue a wake up request by asserting the wakeup

signal. After a hardware reset all of these mask bits are

cleared to enable wake up assertion from all modem lines

and the SIN line. As the wake up operation requires at

least one mask bit to be enabled, the device driver can for

example disable the masks with the exception of the Ring

Indicator, so only a modem ring can wake up the computer

Remaining with the UART, wake-up from the power state

D2 is configurable, and can be triggered by activity on any

combination of modem lines or the serial data input

(EXT_DATA_IN) line. In case of a wake up request from

the EXT_DATA_IN line when the device is in power-state

D2, the clock for that channel is turned on so serial data

framing can be maintained.

For the case of the MIO pins, the state of the MIO pins that

results in wakeup requests is determined by the settings in

the local configuration register MIC. The wakeup behaviour

for these pins, unlike the UART, is not dependant upon the

powerstates D2 or D3. As soon as the correct logic is

invoked than a power management event (wakeup) is

asserted.

When the device issues a wake up request, the

PME_Status bit in the PCI power management registers

(PMCSR[15]) will be set. This is a sticky bit which will only

be cleared by writing a ‘1’ to it. While PME_En (PMCSR[8])

remains set, the PME_Status will continue to assert the

PME# pin or the CSYSCHG pin to inform the device driver

that a power management wake up event has occurred.

After a wake up event is signalled, the device driver is

expected to return the function to the D0 power-state.

6.6.2

Power Reporting

Power Management compliance expects the device to

report state dependant operating data such as power

consumed or heat dissipation. Typically, the data retuned

through the power management DATA register is a static

copy of the function’s worst case “DC characteristics” [PC

Card Standard].

When requested by the DATA_SELECT field, the DATA

Block is required to report the state dependant data and

the DATA_SCALE field is required to return the scaling

factor to be used when interpretating the value of the data

The OXCB950 provides a mechanism for the manufacturer

to download values for the DATA_SCALE and DATA

registers for each of the 16 values of the DATA_SELECT

field. This allows manufacturers to incorporate power

consumption data into the power management registers

specific to their measurements and is available for both

cardbus and pci modes of the device. The facility to load

data into these areas is achieved by utilising the EEPROM

to download into the power management data zone.

Default values assigned to the DATA and DATA_SCALE

areas result in “unknown” values to be interpretated for

each of the 16 possible DATA_SELECT values.

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