ADLINK Technology cPCI-7200, Руководство пользователя

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Double Buffer Mode Principle
Incoming DMA
input data
Circular Buffer
Transfer Buffer
a
b
c
d
> > >
> > > > >
Empty Buffer Untransferred Data Transferred Data
> >
Figure 6-1
The PCI-7200 double buffer mode functions were designed
according to the principle described above. If you use
_7200_DblBufferMode() to enable double buffer mode, the
following _7200_DI_DMA_Start() will perform double-buffered
DMA DI. You can call _7200_CheckHalfReady() to check if data
in the circular buffer is half full and ready for copying to the
transfer buffer. Then you can call _7200_DblBufferTransfer() to
copy data from the ready half buffer to the transfer buffer.
In Win-95 version, W_7200_Alloc_DBDMA_Mem() is needed to
allocates a contiguous DMA memory for the circular buffer. The
buf_size argument of W_7200_Alloc_DBDMA_Mem() is the half
size of circular buffer in byte, that is, the size of each half buffer
in byte. The DMA memory is referenced by the return parameter
handle. This memory is system memory, users are not allowed to
access it directly.