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Memory Services Used During I/O Operations

The DSL provides two routines that help drivers coordinate I/O software with system memory:

• The PrepareMemoryForIO function tells Mac OS that a particular buffer will be used for I/O transfers. It checks memory protection, assigns physical memory to the buffer, provides addressing information, and prepares the processor's caches for the transfer.
• The CheckpointIO function tells the operating system that the previously started transfer is complete. It assures processor cache coherency and either prepares for further transfers or, if its parameters specify that no more transfers will be made, deallocates the resources associated with the buffer preparation. Once the preparation's resources have been deallocated, subsequent I/O operations with the buffer must be preceded by another call to PrepareMemoryForIO.

The memory coordination that these routines provide is summarized in I/O Operations and Memory.