Is there a way to stream 20MS/s data from n-5122 to off-board memory?

[peter cameron]

I have PCI/NI-5122 with 256MB on board memory, need to accomplish ~2GB continuous acquisition on 2 channels at 10MS/sec, total data rate 20MS/sec. Is it possible to stream this data to PC memory continuously? If so, how?

[Travis G.]

Hello Peter,

You've mentioned that you want to transfer about 2GB of data to your PC memory.  Assuming that you have enough memory in your system to accommodate this amount of data, this should be possible.  However, if you dont have greater than 2GB of memory in your system, you will have to effectively stream the data to hard disk, and this may reduce your sustainable sampling rate below 20MS/s.  I would recommend starting with the example program titled niScope EX Fetch Forever.vi found in the LabVIEW Example Finder (Help > Find Examples) for an idea of how to program this type of continuous acquisition.  With this example, each call the niScope Fetch function will initiate a DMA (Direct Memory Access) transfer of data from the onboard memory of the device to your PC memory.  If at any point your system cannot keep up and data is overwritten on the onboard memory of the device, the NI-Scope driver will throw an error.  Give this example a try and let us know if you have any further questions.

Regards,
Travis G.
Applications Engineering
National Instruments
www.ni.com/support

[peter cameron]

ok, thanks, will try what you suggests

[DFGray]

Unfortunately, you will not be able to save 2GBytes of data in your system memory.  You may get up to about 1.4GBytes if you go through a lot of pain.  Doing it the easy way, the maximum you will get is somewhere between 0.8 and 1.1 GBytes, depending on your version of LabVIEW.  For details of why, see the tutorial Managing Large Data Sets in LabVIEW.  You need to stream to disk.

Fortunately, with a relatively modern computer, this is fairly easy.  The weak link will be your disk drive.  If you have problems keeping up, do a defrag and try again.  Use NI-HWS for the file storage.  It was designed for exactly this task.  If you have LV8.0 or better, you can also use the file primitives, but I would still recommend HWS.  It takes care of a lot of details for you.  Older versions of LV make it challenging to save more than 2GBytes of LV, and you can't do it if you are not using Windows with an NTFS file system.  A FAT32 file system limits file size to 2GBytes.

Let us know if you need more info.