mandelbrot

Mandelbrot Set

This SystemVerilog demo uses fixed-point multiplication and a small framebuffer to render the Mandelbrot set.

This design has an associated Project F blog post: Mandelbrot in Verilog.

I've included project files for:

• Digilent Arty A7-35T
• Digilent Nexys Video
• Verilator/SDL Simulation

This demo makes use of modules from the Project F library.

Mandelbrot set rendered by Verilator/SDL.

Demo Parameters

We consider up to 255 iterations by default, but you can adjust this by changing ITER_MAX in the top module. The minimum number of iterations supported is 128, but you get the best results with 2ⁿ-1, for example, 511, as this best uses the full range of colours.

With the default 25-bit precision, you can zoom in 15 times to a minimum step of 1/2²¹. You can adjust the precision by changing FP_WIDTH in the top module (don't forget to adjust X_START, Y_START, and STEP).

Xilinx 7-Series FPGAs

This demo have been tested with:

• Vivado 2022.2

Arty A7-35T Build

To create a Vivado project for the Digilent Arty A7-35T with Pmod VGA; clone the projf-explore git repo, then start Vivado and run the following in the Tcl console:

cd projf-explore/demos/mandelbrot/xc7-vga/arty-a7-35
source ./create_project.tcl

You can then build top_mandel as you would for any Vivado project.

Button controls:

• BTN2 - left/up/zoom-out
• BTN1 - select mode: horizontal/vertical/zoom
• BTN0 - right/down/zoom-in
• RESET - return to starting coordinates and zoom

NB. Controls don't work if rendering is in progress.

Four green LEDs show status:

• LD7 - rendering in progress
• LD6 - horizontal motion
• LD5 - vertical motion
• LD4 - zoom

Nexys Video DVI Build

To create a Vivado project for the Digilent Nexys Video with DVI output; clone the projf-explore git repo, then start Vivado and run the following in the Tcl console:

cd projf-explore/demos/mandelbrot/xc7-dvi/nexys-video
source ./create_project.tcl

You can then build top_mandel as you would for any Vivado project.

Button controls:

• BTNU - left/up/zoom-out
• BTNC - select mode: horizontal/vertical/zoom
• BTND - right/down/zoom-in
• CPU_RESET - return to starting coordinates and zoom

NB. Controls don't work if rendering is in progress.

Four green LEDs show status:

• LD3 - rendering in progress
• LD2 - horizontal motion
• LD1 - vertical motion
• LD0 - zoom

Verilator

This demo have been tested with:

• Verilator 4.038 (Ubuntu 22.04 amd64)
• Verilator 5.006 (macOS 13 arm64)

Verilator Build

If this is the first time you've used Verilator and SDL, you need to install dependencies.

Build the demo:

cd projf-explore/demos/mandelbrot/verilator-sdl
make

Run the simulation executable from obj_dir:

./obj_dir/mandelbrot

Keyboard controls:

• Up Arrow - left/up/zoom-out
• Space Bar - select mode: horizontal/vertical/zoom
• Down Arrow - right/down/zoom-in

NB. Controls don't work if rendering is in progress.

You can quit the simulation by pressing the Q key.

To run in fullscreen mode, edit main_mandelbrot.cpp so that FULLSCREEN = true, then rebuild.