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Device DMA, Sub-Buffers, and Callbacks (Blackfin, Embedded Module)

Many device drivers in the Embedded Module for Blackfin Processors use DMA (direct memory access) to fill the device buffers. After you enable the device, data transfer from the device to the buffer is automatic. For a device that receives data, such as an ADC, the device indicates that the buffer is full using a callback event. If you wire a callback VI reference to the device open VIs, the execution is passed to the calling VI. You can set a global flag inside the callback to indicate the buffer is ready to be processed. Use sub-buffers if you do not want to lose data while the buffer is being processed. Use the BF Device Initialize Buffer VI to create sub-buffers. Refer to the VisualDSP++ 4.5 Device Drivers and System Services Manual for Blackfin Processors on the Analog Devices Web site at www.analog.com for information about sub-buffers.

Use the device-specific Wait on Data Ready Flag VIs and the Clear Data Ready Flag VIs instead of a callback VI if you want to set a flag when the device buffer is full. The device-specific Wait on Data Ready Flag VIs return the sub-buffer reference only when the device buffer is full. Use the sub-buffer reference to obtain the buffer contents. Call the device-specific Clear Data Ready Flag VI after the buffer processing is complete.


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