Jump to content
Вадим Ладик

myRIO ADC, max sample rate

Recommended Posts

Hello colleagues! I have a next task: It is necessary to get analog data from 4 ADC channels of myRIO with max sample rate. As we know myRIO has max rate 500 kS/s for all channels. So we have 125 kS/s per channel (500/4). It's good. A question in the next: how I can send data from FPGA target to RT in this case? I have tried to use large size FIFO buffer (target to host) but got compilation error. As I understood FIFO buffer doesn't use external memory for data storage and uses FPGA resources. The next step I think to use max available size buffer and interrupt on host when buffer is full, but in this case I will probably get skips in data stream, because interrupt requires about 400 us. Can I read data from buffer on RT level with invoke node in parallel data writing on FPGA target? Will there be an overlay in this case? And where I can read any info about fast data logging with RIO platform?

choose files... Click to choose files

Thank you for your help.

Capture.PNG

Edited by Вадим Ладик

Share this post


Link to post
Share on other sites

The DMA FIFO is what you're looking for with the data transfer.

Edited by Tim_S

Share this post


Link to post
Share on other sites

I've gotten a test bench of 1 MS/sec of 32-bit data (24-bits plus 8-bits channel identifier) across FPGA->RT->Windows using DMA channel to RT FIFO to TCP and let it run overnight without drop of any data. Buffer was set to maximum size of U32. Now that was with a cRIO rather than a myRIO. 

Are you using NI's recommendations for best practices? Particularly the one where you check for available (request 0 samples) and then read all is a good way to read on the RT side. If you wait until the buffer is full then the FPGA can (and almost certainly will) overwrite before host side can service an interrupt.

  • Like 1

Share this post


Link to post
Share on other sites

The DMA FIFO is silly fast if configured correctly. I have used it in a VST to losslessly stream (continuously for tens of hours) something on the order of several GB/s to disk. That was using PXI, and not myRIO though.

Don't forget, the host (RT) is actually the place where data gets buffered, and this is where you can make a nice big buffer. You don't really need a big buffer on the FPGA, you just need to make sure you read from the host buffer fast enough. As Tim_S said, do the trick where you read zero samples, this will return no data but will give you the number of samples actually available.

  • Like 1

Share this post


Link to post
Share on other sites
On 9/4/2019 at 7:03 PM, Tim_S said:

I've gotten a test bench of 1 MS/sec of 32-bit data (24-bits plus 8-bits channel identifier) across FPGA->RT->Windows using DMA channel to RT FIFO to TCP and let it run overnight without drop of any data. Buffer was set to maximum size of U32. Now that was with a cRIO rather than a myRIO. 

Are you using NI's recommendations for best practices? Particularly the one where you check for available (request 0 samples) and then read all is a good way to read on the RT side. If you wait until the buffer is full then the FPGA can (and almost certainly will) overwrite before host side can service an interrupt.

 

19 hours ago, Neil Pate said:

The DMA FIFO is silly fast if configured correctly. I have used it in a VST to losslessly stream (continuously for tens of hours) something on the order of several GB/s to disk. That was using PXI, and not myRIO though.

Don't forget, the host (RT) is actually the place where data gets buffered, and this is where you can make a nice big buffer. You don't really need a big buffer on the FPGA, you just need to make sure you read from the host buffer fast enough. As Tim_S said, do the trick where you read zero samples, this will return no data but will give you the number of samples actually available.

 

Thank you for your help! I have gotten a necessary result with max sample rate (500 kHz).

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.