Intel LPCI-7200S manual Double Buffer Mode Principle

The PCI-7200 double buffer mode functions were designed according to the principle described above. If using _7200_DblBufferMode() to enable double buffer mode, _7200_DI_DMA_Start() will perform double-buffered DMA DI. Call _7200_CheckHalfReady() to check if data in the circular buffer is half-full and ready for copying to the transfer buffer. Then call _7200_DblBufferTransfer() to copy data from the ready half buffer to the transfer buffer.

In Windows 95, 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.

60 • Double Buffer Mode Principle