Describes the pin direction functions involved in implementing the GPIO interface class.
Pins are used as inputs or outputs of binary signals. The GPIO
interface class does not support bidirectional pins. However, some
platforms allow pins to be in a quiescent state (also called floating
or tri-stated). In this case a pin can be in one of three logical
states namely, True, False or quiescent as specified in the enumeration TGpioDirection. The relevant three-valued logic is specified
in this table.
Implement SetPinDirection() for
each value of the enumeration TGpioDirection.
Implement SetPinDirection() with aDirection == EInput and return value KErrNone.
Set the pin to behave as an input binary signal.
Implement SetPinDirection() with aDirection == EOutput and return value KErrNone.
Set the pin to behave as an output binary signal.
Implement SetPinDirection() with aDirection == ETriStated and return value KErrNone.
Set the pin to be in a quiescent state (also called floating or deactivated).
Only implement this if the platform supports the quiescent state. The physical state of the pin will be determined by the drive on the line.
Implement SetPinDirection() with return value KErrNotSupported.
Return KErrNotSupported if the pin cannot operate in the direction specified,
for instance if ETriStated has been
passed and the platform does not support the quiescent
state.
Implement GetPinDirection() for
each value of the enumeration TGpioDirection.
Implement GetPinDirection() with aDirection containing EInput and return value KErrNone.
Verify that the pin is behaving
as a binary input signal. Set aDirection to EInput
Implement GetPinDirection() with aDirection containing EOutput and return value KErrNone.
Verify that the pin is behaving
as a binary output signal. Set aDirection to EInput
Implement GetPinDirection() with aDirection containing ETriStated and return value KErrNone.
Verify that the pin is in the quiescent
state. Set aDirection to ETriStated
Implement GetPinDirection() with return value KErrNotSupported.
Return KErrNotSupported if reading the pin direction is not supported.