PFREE_MAP_REGISTERS callback function (wdm.h)
The FreeMapRegisters routine releases a set of map registers that were saved from a call to AllocateAdapterChannel.
Syntax
PFREE_MAP_REGISTERS PfreeMapRegisters;
void PfreeMapRegisters(
[in] PDMA_ADAPTER DmaAdapter,
[in] PVOID MapRegisterBase,
[in] ULONG NumberOfMapRegisters
)
{...}
Parameters
[in] DmaAdapter
Pointer to the DMA_ADAPTER structure returned by IoGetDmaAdapter that represents the bus-master adapter or DMA controller.
[in] MapRegisterBase
Specifies the map registers allocated for the DMA operation. The system passes this value to the driver's AdapterControl routine.
[in] NumberOfMapRegisters
Specifies the number of map registers to be released. This value must match the number specified in an earlier call to AllocateAdapterChannel.
Return value
None
Remarks
FreeMapRegisters is not a system routine that can be called directly by name. This routine is only callable by pointer from the address returned in a DMA_OPERATIONS structure. Drivers obtain the address of this routine by calling IoGetDmaAdapter.
When the driver of a bus-master device has completed the current packet-based DMA transfer request, it calls FreeMapRegisters to release the map registers previously allocated by a call to AllocateAdapterChannel and retained because its AdapterControl routine returned DeallocateObjectKeepRegisters. The driver must call FreeMapRegisters after calling FlushAdapterBuffers.
Requirements
| Requirement | Value |
|---|---|
| Minimum supported client | Available starting with Windows 2000. |
| Target Platform | Desktop |
| Header | wdm.h (include Wdm.h, Ntddk.h, Ntifs.h) |
| IRQL | DISPATCH_LEVEL |
| DDI compliance rules | IrqlDispatch(storport), IrqlDispatch(storport), IrqlDispatch(wdm) |