© National Instruments
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9
Bus Interface
The bus interface circuitry of NI 6614 efficiently moves data between host memory and the
measurement and acquisition circuits.
Data Transfer Methods
Refer to the following sections for information about bus interface data transfer methods for
devices.
PXI Express Device Data Transfer Methods
The primary ways to transfer data across the PXI Express bus are as follows:
•
Direct Memory Access (DMA)
—DMA is a method to transfer data between the device
and computer memory without the involvement of the CPU. This method makes DMA the
fastest available data transfer method. NI uses DMA hardware and software technology to
achieve high throughput rates and increase system utilization. DMA is the default method
of data transfer for PXI Express devices.
NI 6614 devices have ten fully-independent DMA controllers for high-performance
transfers of data blocks. One DMA controller is available for each measurement and
acquisition block:
–
Counter 0
–
Counter 1
–
Counter 2
–
Counter 3
–
Counter 4
–
Counter 5
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Counter 6
–
Counter 7
–
Digital waveform generation (digital output)
–
Digital waveform acquisition (digital input)
Each DMA controller channel contains a FIFO and independent processes for filling and
emptying the FIFO. This allows the buses involved in the transfer to operate independently
for maximum performance. Data is transferred simultaneously between the ports. The
DMA controller supports burst transfers to and from the FIFO.
