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Altera_Forum
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11 years ago

Live Control of PWM Outputs (need advice)

I've been searching around google for how to implement what I need but I'm not understanding the underlying ideas as a whole, and I'm hoping for some explanation and advice.

My project: Generate several PWM outputs. The frequency/phase/dutycycle should all be controllable WHILE the FPGA is running (if this is even possible?).

My hardware: Altera DE0 Nano board

What I understand so far (I think):

I need to make some sort of live prompt on the screen where the user enters values for the freq/phase/dutycycle. I'm assuming this requires underlying C/C++ to read the keystrokes.

I've written Verilog that uses a counter to turn the PWM outputs on/off according to a duty cycle parameter, as well as a shift register to introduce phase shifting to the outputs.

I don't understand how to use keyboard input or even C/C++ code to change the Verilog module's parameters as the FPGA is running.

The closest thing I can think of is using a NiosII with a C software application, but this would require the user to rebuild and run after every parameter is changed.

Also, I assume there is some sort of Altera IP for PWM outputs, but my searches have given me nothing.

I would really appreciate at least a high level explanation of how one can control Verilog parameters while the FPGA is running and how C code in NIOSII interacts with a Verilog module.

Thank you for any help you can give!

1 Reply

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    11 years ago

    If you're not already using Qsys/SOPC Builder, then probably the easiest method is to use the In-System Sources and Probes (http://www.altera.com/literature/hb/qts/qts_qii53021.pdf). This allows you instantiate a megafunction which you connect to your control registers, and allows you to easily modify their content using a PC GUI that Altera provides.

    Otherwise, you should consider adding an Avalon-MM Slave interface to your block and packaging it as a Qsys component. This would allow you to write NIOS C software to modify it if you wanted to, or it would also allow you to use the System Console (another Altera PC GUI) to read/write your register values; you can even create simple GUI's using the Dashboard functionality of that tool. An alternate approach would be to instantiate a series of GPIO blocks and connect them to the control registers of your block (instead of adding the Avalon-MM Slave port to your block).

    From your description though, it sounds like In-System Sources and Probes is both less work and adequate for what you are trying to accomplish.