Fetch Waveform (Direct DMA)
- Updated2023-02-17
- 4 minute(s) read
Fetch Waveform (Direct DMA)
Transfers acquired waveform data from device memory directly to PC memory allocated by a Direct DMA-compatible device.
Inputs/Outputs
session in
Instrument session obtained from the Initialize Acquisition Sessionnode, the Initialize Generation Sessionnode, or the Initialize External Calibrationnode.
error in
Error conditions that occur before this node runs.
The node responds to this input according to standard error behavior.
Default value: No error
samples to read
The specified number of samples to fetch.
If you specify a value for samples to read that is greater than the number of samples in the device memory, NI-HSDIO returns the samples that are acquired after max time milliseconds. Setting this parameter to -1 acquires the samples per record specified in the niHSDIO Configure Acquisition Sizenode.
maximum time (ms)
The time, in milliseconds, allotted for the node to complete before NI-HSDIO returns a timeout error.
If you set the value to -1, the node never times out. If you set this parameter to 0, the node returns immediately with up to the number of samples specified in samples to read.
If samples to read is greater than the number of samples in the device memory and all the available samples are acquired before a timeout, NI-HSDIO returns the available samples.
Default value: 10000
record to fetch
Parameter that specifies which record you want to fetch from onboard memory.
buffer address
The location for the buffer in memory at which to transfer acquired data.
buffer size
The size (in bytes) of the buffer in memory at which to transfer acquired data.
session out
Handle that identifies the session in all subsequent node calls.
The session out parameter is obtained from the Initialize Acquisition Sessionnode or the Initialize Generation Sessionnode.
error out
Error information.
The node produces this output according to standard error behavior.
offset to first sample
The offset of the first sample acquired within the specified buffer. Data transferred from device memory in 128 byte increments, so the first sample of the acquired data typically occurs at some offset from the start of the buffer when using a Reference trigger.
waveform info
The absolute and relative timestamp for the operation, the dt, and the actual number of samples read.
absolute timestamp
absolute timestamp returns the absolute timestamp for the operation.
relative timestamp
relative timestamp returns the relative timestamp for the operation.
dt
dt returns the time between values in the waveform.
actual samples read
The returned number of samples read.
reserved 1
reserved 1 is reserved for future use.
reserved 2
reserved 2 is reserved for future use.