ADLINK Technology NuDAQ User Manual

Also see for NuDAQ: User guide User manual

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ADLINK Technology NuDAQ User Manual Manual pdf 91 page image

Double Buffer Mode Principle 796 Double Buffer Mode PrincipleThe data buffer for a double-buffered DMA DI operation is logicallya circular buffer divided into two equal halves. The double bufferedDI begins when the device starts writing data into the first half ofthe circular buffer (Figure 6-1a). After device begins writing to thesecond half of the circular buffer, users can copy the data from thefirst half into the transfer buffer (Figure 6-1b). Users can now pro-cess the data in the transfer buffer according to application needs.After the board has filled the second half of the circular buffer, theboard returns to the first half buffer and overwrites the old data.Users can now copy the second half of the circular buffer to thetransfer buffer (Figure 6-1c). The data in the transfer buffer isagain available for process. The process can be repeated end-lessly to provide a continuous stream of data to applications (Fig-ure 6-1d).Figure 6-1: Double Buffer ModeThe PCI-7200 double buffer mode functions were designedaccording 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 isIncoming DMAinput data Circular BufferTransfer Buffera bc d> > >> > >> >Empty Buffer Untransferred Data Transferred Data> >