Generating a Digital Waveform Larger than Memory on PXI Cards

[iBrow]

Hello,

I'm looking for a means of sending large digital waveforms using a PXI Digital Waveform Generator. I looked at the HS DIO Cards, but their memory is smaller than the files that I want to transfer. My understanding is that the bandwidth of the PXI Backplane is 132 Mb/s. Therefore, shouldn't I be able to continuously stream out a digital signal from the processor memory to the card that is slower than that? For instance, 50 Mbits / second (equivalent to only 6.25 Mb/s)? However, my understanding after reading their manuals is that you cannot continuously stream a large waveform file from processer memory, you must transfer the file to the board memory first, and then transfer that out.

Does anyone know if there is a way to have a digital waveform generation card stream an arbitrarily large digital waveform straight from processor memory? Or, what is the fastest digital waveform generation pxi card that does not require the files to be put into board memory first?

Thanks

Isaac

[RT4CY · Accepted solution]

Hello Isaac,

Take a look at the following developer zone.

NI-HSDIO Stream from Disk (Generation) Using Win32 File IO

Note that you will not be able to take full advantage of the maximum update rates of the HSDIO devices, because the data needs to be transferred across a bus.  Some other considerations are the data width as well as the HSDIO device you select, which may depend on other requirements not related to file or waveform size (for example the voltage standard or whether you need hardware compare).  For more information, take a look at the following developer zone articles.

Data Streaming Architectures in PXI Systems
How to Use the National Instruments Logic Analyzer and Pattern Generator Solution

Advanced Features of High-Speed Digital I/O Devices White Paper Series

[iBrow]

Thanks. That was exactly the information I needed.

[RT4CY]

No problem at all!  I know that you mentioned you have existing files which exceed the onboard memory of our boards.  One interesting article from the advanced features of HSDIO whitepaper series is the following.

Advanced Features of High Speed Digital I/O devices : Scripting In High Speed Digital I/O Boards

The ability to loop waveforms is a powerful feature of scripting which helps conserve memory.  Take a look at the Memory Utilization section of the article linked above for more information.  Creating scripts that loop waveforms may get you within the limits of the onboard memory of the device.  Generating from device memory will allow you to utilize the full updata rate of the HSDIO board as well as minimize the processor of the system controller.

Message Edited by RT4CY on 10-05-2009 01:00 PM