DMA Abstraction Layer (Compact 7)
3/12/2014
Windows Embedded Compact 7 includes a direct memory access (DMA) abstraction library with which you can implement DMA support in a bus-independent manner. The purpose of the DMA abstraction library is to create an interface with which a device driver developer can implement DMA support, and also to provide an interface for platform-dependent DMA handler routines. By using the DMA abstraction library functions you can use an onboard or built-in DMA controller through a chip-specific DMA driver that works with a standard set of bus-independent DMA functions.
The DMA abstraction framework is made up of three components:
- The DMA model device driver (MDD)
- The DMA platform dependent driver (PDD)
- The DMA abstraction functions of CEDDK.dll
CEDDK.dll forwards all function requests to the DMA driver by using IOCTLs. The following table lists the CEDDK.dll functions that are included in the DMA abstraction layer.
| Function | Description |
|---|---|
Prepares the system for a DMA operation on behalf of the target device. |
|
Frees a DMA channel buffer that DMAAllocateChannel allocated, together with all the resources that the DMA channel uses to transfer data. |
|
Maps a virtual buffer to a physical DMA block. |
|
Returns the length and physical address of a DMA buffer block that DMAOpenBuffer creates. |
|
Returns the length and physical address of a DMA buffer block that DMAOpenBuffer creates to map a virtual buffer to physical memory. |
|
Manually flushes the DMA buffer block to regain cache coherency. |
|
Frees all resources that DMAOpenBuffer allocates to map a virtual buffer to a physical DMA block. |
|
Puts a DMA transfer into auto start mode. |
|
Queues multiple DMA transfer requests. |
|
Sets up map descriptor registers for a channel to map a DMA channel from a locked buffer. This function fails if other DMA transfers are queued in the DMA channel. |
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Sets up map descriptor registers for a channel to map a DMA transfer from a locked buffer. If other DMA transfers are queued in the DMA channel, this function queues this transfer. |
|
Directly controls hardware-mapped DMA transfers, unless the transfer is already completed or is not queued. |
|
Starts a subordinate DMA transfer that uses an associated memory block. |
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Gets the current active or queued DMA transfer status. |
|
Retrieves DMA transfer object context values. |
|
Cancels an active DMA transfer. |
|
Closes a DMA transfer and releases all related resources. |
For more information about these functions, see the reference information for each function.