Usb Device Data Transfer Methods - National Instruments DAQ X Series User Manual

Chapter 10 Bus Interface
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USB Device Data Transfer Methods

The primary ways to transfer data across the USB bus are as follows:
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X Series User Manual
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– 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
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.
X Series USB 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
10-2
Output, for more information.
Output, for more information.
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