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IOLittleMemoryCursor

Overview

An IOMemoryCursor subclass that outputs a vector of PhysicalSegments in the little endian byte order.

Discussion

The IOLittleMemoryCursor would be used when the DMA hardware requires a little endian address and length pair. This cursor outputs an array of PhysicalSegments that are encoded in little endian format.

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Functions

getPhysicalSegments

Generates a little endian physical scatter/gather list given a memory descriptor.

initWithSpecification

Primary initializer for the IOLittleMemoryCursor class.

outputSegment

Outputs the given segment into the output segments array in little endian byte order.

withSpecification

Creates and initializes an IOLittleMemoryCursor in one operation.

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getPhysicalSegments

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Generates a little endian physical scatter/gather list given a memory descriptor.

public

virtual UInt32 getPhysicalSegments(
    IOMemoryDescriptor *descriptor, 
    IOByteCount fromPosition, 
    PhysicalSegment *segments, 
    UInt32 maxSegments, 
    UInt32 maxTransferSize = 0, 
    IOByteCount *transferSize = 0)  

Parameters

descriptor

IOMemoryDescriptor that describes the data associated with an I/O request.

fromPosition

Starting location of the I/O within a memory descriptor.

segments

Pointer to an array of IOMemoryCursor::PhysicalSegments for the output physical scatter/gather list.

maxSegments

Maximum number of segments that can be written to segments array.

maxTransferSize

Maximum transfer size is limited to that many bytes, otherwise it defaults to the maximum transfer size specified when the memory cursor was initialized.

transferSize

Pointer to an IOByteCount variable that can contain the total size of the transfer being described. Defaults to 0 indicating that no transfer size need be returned.

Return Value

If the descriptor is exhausted of memory, a zero is returned, otherwise the number of segments that were filled in is returned.

Discussion

Generates a list of physical segments from the given memory descriptor, relative to the current position of the descriptor. Wraps IOMemoryCursor::genPhysicalSegments.

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initWithSpecification

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Primary initializer for the IOLittleMemoryCursor class.

public

virtual bool initWithSpecification(
    IOPhysicalLength maxSegmentSize, 
    IOPhysicalLength maxTransferSize, 
    IOPhysicalLength alignment = 1); 

Parameters

maxSegmentSize

Maximum allowable size for one segment. Defaults to 0.

maxTransferSize

Maximum size of an entire transfer. Defaults to 0 indicating no maximum.

alignment

Alignment restrictions on output physical addresses. Not currently implemented. Defaults to single byte alignment.

Return Value

Returns true if the inherited classes and this instance initialize successfully.

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outputSegment

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Outputs the given segment into the output segments array in little endian byte order.

public

static void outputSegment(
    PhysicalSegment segment, 
    void *segments, 
    UInt32 segmentIndex); 

Parameters

segment

The physical address and length that is next to be output.

segments

Base of the output vector of DMA address length pairs.

segmentIndex

Index to output 'segment' in the 'segments' array.

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withSpecification

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Creates and initializes an IOLittleMemoryCursor in one operation.

public

static IOLittleMemoryCursor * withSpecification(
    IOPhysicalLength maxSegmentSize, 
    IOPhysicalLength maxTransferSize, 
    IOPhysicalLength alignment = 1); 

Parameters

maxSegmentSize

Maximum allowable size for one segment. Defaults to 0.

maxTransferSize

Maximum size of an entire transfer. Defaults to 0 indicating no maximum.

alignment

Alignment restrictions on output physical addresses. Not currently implemented. Defaults to single byte alignment.

Return Value

Returns a new memory cursor if successfully created and initialized, 0 otherwise.

Discussion

Factory function to create and initialize an IOLittleMemoryCursor in one operation. See also IOLittleMemoryCursor::initWithSpecification.

#defines

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littleOutputSegment

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#define littleOutputSegment IOLittleMemoryCursor::outputSegment 

Discussion

Backward compatibility define for the old global function definition. See also IOLittleMemoryCursor::outputSegment.

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Last Updated: 2008-12-19