Data Acquisition Toolbox

TransferMode

Specify how data is transferred from the data acquisition device to system memory

Description

For National Instruments hardware, TransferMode can be Interrupts or SingleDMA for both analog input and analog output subsystems. If TransferMode is Interrupts, then data is transferred from the hardware first-in, first-out memory buffer (FIFO) to system memory using interrupts. If TransferMode is SingleDMA, then data is transferred from the hardware FIFO to system memory using a single direct memory access (DMA) channel. Some boards also support a TransferMode of DualDMA for analog input subsystems. For example, the AT-MIO-16E-1 board supports this transfer mode. If TransferMode is DualDMA, then data is transferred from the hardware FIFO to system memory using two DMA channels. Depending on your system resources, data transfer via interrupts can significantly degrade system performance.

For Measurement Computing hardware, TransferMode can be Default, InterruptPerPoint, DMA, or InterruptPerBlock. If TransferMode is Default, the transfer mode is automatically selected by the driver based on the board type and the sampling rate. If TransferMode is InterruptPerPoint, a single conversion is transferred for each interrupt. You should use this property value if your sampling rate is less the 5 kHz or you specify a small block size for memory buffering (as defined by the BufferingConfig property). If TransferMode is DMA, data is transferred using a single DMA channel. If TransferMode is InterruptPerBlock, a block of data is transferred for each interrupt. You should use this property value if your sampling rate is greater than 5 kHz and you are using a board that has a fast maximum sampling rate. Note that a data block is defined by the board, and usually corresponds to half the FIFO size.

For Keithley hardware, TransferMode can be Interrupts or DMA. If TransferMode is Interrupts, then data is transferred from the hardware first-in, first-out memory buffer (FIFO) to system memory using interrupts. If TransferMode is DMA, then data is transferred from the hardware FIFO buffer to system memory using a single DMA channel. Note that if bus mastering is disabled in the DriverLINX Configuration panel for the device, then DMA is not offered as an option.

Note    If your sampling rate is greater than around 5 kHz, you should avoid using interrupts if possible. The recommended TransferMode setting for your application will be described in your hardware documentation, and depends on the specific board you are using and your platform configuration.

Characteristics

Vendor	Keithley, Measurement Computing, National Instruments
Usage	AI, AO, Common
Access	Read/write
Data type	String
Read-only when running	Yes

Values

Keithley

DMA	Transfer data using a single DMA channel.
Interrupts	Transfer data using interrupts.

If bus mastering is disabled in the DriverLINX configuration panel for the device, then DMA is not available, and the default is set to Interrupts.

Measurement Computing

{Default}	The transfer mode is automatically selected by the driver based on the board type and the sampling rate.
InterruptPer Point	Transfer single data points using interrupts.
DMA	Transfer data using a single DMA channel (AI only).
InterruptPer Block	Transfer a block of data using interrupts (AI only).

National Instruments

Interrupts	Transfer data using interrupts.
SingleDMA	Transfer data using a single DMA channel.
DualDMA	Transfer data using two DMA channels.

This default property value is supplied by the driver. For most devices that support data transfer via interrupts and DMA, SingleDMA is the default value.

Sum

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