FPGA Square Wave on Waveform Problem (DMA Transfer)

[Edwarde]

Hi to everyone,

I would like to produce internal square wave which frequency is controlled by Frequency Control component in FPGA.
Then, sent it to Host.vi and show square wave on Waveform Chart.  When I change frequency, it needs to effect instantly waveform chart about square wave. This should be effective in terms of transferring data. I am using FIFO DMA transfer to Host.vi.
We can think this like oscilloscope on PC.

I am getting square wave on Waveform Chart but when I change frequency, it produces same square wave. How should I handle this problem?

What I am using:

1. Square wave generator that produces square wave which gets frequency from my Frequency Control component.
2. It writes to FIFO.Write
3. Then I read it from Host.vi FIFO.Read

Thank you.

[speleato]

One thing that comes to mind is that the DMA FIFO has a couple of buffers (one on the FPGA and one on the host) which could be full of old data. How quickly are you writing data on the FPGA and how quickly are you reading data on the Host?

Does the frequency shown on the host eventually change if you wait long enough?

Sebastian