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IODBDMAMemoryCursor

Overview

An IOMemoryCursor subclass that outputs a vector of DBDMA descriptors where the address and length are filled in.

Discussion

The IODBDMAMemoryCursor would be used when the DBDMA hardware is available for the device for that will use an instance of this cursor.

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Functions

getPhysicalSegments

Generates a DBDMA physical scatter/gather list given a memory descriptor.

initWithSpecification

Primary initializer for the IODBDMAMemoryCursor class.

outputSegment

Outpust the given segment into the output segments array in address and length fields of an DBDMA descriptor.

withSpecification

Creates and initializes an IODBDMAMemoryCursor in one operation.

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getPhysicalSegments

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Generates a DBDMA physical scatter/gather list given a memory descriptor.

public

virtual UInt32 getPhysicalSegments(
    IOMemoryDescriptor *descriptor, 
    IOByteCount fromPosition, 
    IODBDMADescriptor *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 DBDMA descriptors for the output physical scatter/gather list. Be warned no room is left for a preamble in the output array. 'segments' should point to the first memory description slot in a DBDMA command.

maxSegments

Maximum number of segments that can be written to the DBDMA descriptor table.

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 DBDMA descriptors where the address and length fields are filled in appropriately. But the client is expected to fill in the rest of the DBDMA descriptor as is appropriate for their particular hardware. Wraps IOMemoryCursor::genPhysicalSegments.

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initWithSpecification

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Primary initializer for the IODBDMAMemoryCursor 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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Outpust the given segment into the output segments array in address and length fields of an DBDMA descriptor.

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 IODBDMAMemoryCursor in one operation.

public

static IODBDMAMemoryCursor * 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 IODBDMAMemoryCursor in one operation. See also IODBDMAMemoryCursor::initWithSpecification.

#defines

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dbdmaOutputSegment

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#define dbdmaOutputSegment IODBDMAMemoryCursor::outputSegment 

Discussion

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

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Last Updated: 2008-12-19