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Logical and Physical Memory Preparation

The two most common PrepareMemoryForIO operations are preparing logical or physical I/O when the client has specified a single, logically-addressed buffer. The following lists show how the driver would set up the IOPreparationTable for these cases. The only difference between the two cases is which mapping table is supplied. PrepareMemoryForIO infers whether the transfer will be physical (DMA) or logical (programmed I/O) based on whether the mapping table is physical or logical.

To perform logical I/O with single logical buffer, set IOPreparationTable as follows:

`options`	`kIOLogicalRanges` and either `kIOIsInput` or `kIOIsOutput`
`addressSpace`	address parameter used in the `DoDriverIO` call addressSpace
`granularity`	0
`firstPrepared`	0
`mappingEntryCount`	Number of pages in buffer
`logicalMapping`	Address of table containing `mappingEntryCount` entries
`physicalMapping`	`nil`
`range.base`	Buffer address
`range.length`	Buffer length

For physical I/O with single logical buffer, set IOPreparationTable as follows:

`options`	`kIOLogicalRanges` and either `kIOIsInput` or `kIOIsOutput`
`addressSpace`	address parameter used in the `DoDriverIO` call
`granularity`	0
`firstPrepared`	0
`mappingEntryCount`	Number of pages in buffer
`logicalMapping`	`nil`
`physicalMapping`	Address of table containing `mappingEntryCount` entries
`range.base`	Buffer address
`range.length`	Buffer length