National Instruments DAQ X NI 634 Series, Руководство пользователя

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Chapter 10 Bus Interface
– 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.
Each DMA controller supports several features to optimize PCI Express/PXI Express bus
utilization. The DMA controllers pack and unpack data through the FIFOs. This feature
allows the DMA controllers to combine multiple 16-bit transfers to the DAQ circuitry into
a single 32-bit burst transfer on PCI Express. The DMA controllers also automatically
handle unaligned memory buffers on PCI Express/PXI Express.
• Programmed I/O —Programmed I/O is a data transfer mechanism where the user’s
program is responsible for transferring data. Each read or write call in the program initiates
the transfer of data. Programmed I/O is typically used in software-timed (on-demand)
operations. Refer to the
Analog Output Data Generation Methods section of Chapter 5,
Analog Output , for more information.
USB Device Data Transfer Methods
The primary ways to transfer data across the USB bus are as follows:
•
USB Signal Stream
—USB Signal Stream is a method to transfer data between the device
and computer memory using USB bulk transfers without intervention of the
microcontroller on the NI device. NI uses USB Signal Stream hardware and software
technology to achieve high throughput rates and increase system utilization in USB
devices.
USB X Series devices have eight fully-independent USB Signal Stream for
high-performance transfers of data blocks. These channels are assigned to the first
eight measurement/acquisition circuits that request one.
•
Programmed I/O
—Programmed I/O is a data transfer mechanism where the user’s
program is responsible for transferring data. Each read or write call in the program initiates
the transfer of data. Programmed I/O is typically used in software-timed (on-demand)
operations. Refer to the
Analog Output Data Generation Methods section of Chapter 5,
Analog Output , for more information.