Data Acquisition Toolbox™

TransferMode

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

Description

For National Instruments^® NI-DAQmx hardware, this property is ignored. The device driver automatically selects the most efficient transfer mode available.

For National Instruments Tradional NI-DAQ 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, InterruptPerBlock, or InterruptPerScan.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. If TransferMode is InterruptPerScan, data is not transferred until the entire scan is complete. This can only be used when the number of points acquired is less than or equal to the FIFO size. You should use this mode if your sampling rate is higher than the maximum continuous scan rate of the data acquisition device.

For Keithley^® hardware, TransferMode can be Interrupts or DMA. If TransferMode is Interrupts, then data is transferred from the hardware First In, First Out (FIFO) memory buffer 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 ~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

Values

Advantech^®

Keithley^®

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.

Note   Keithley and VXI Technology adaptors will be deprecated in a future version of the toolbox. If you create a Data Acquisition Toolbox™ object for the keithley or hp1432 adaptors in R2007a, you will receive a warning stating that these adaptors will be removed in a future release. See the supported hardware page at www.mathworks.com/products/daq/supportedio.html for more information.

Measurement Computing™

National Instruments^®

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.

Examples

Set the TransferMode property for a National Instruments board before acquiring data.

ai = analoginput('nidaq', 'Dev1');
set(ai, 'TransferMode', 'SingleDMA');
addchannel(ai, 1:2);
softscope(ai)

Sum

Block Reference