4 VGA Mandelbrot
4 : VGA Mandelbrot
- Author: Mike Bell
- Description: Mandelbrot on VGA, racing the beam
- GitHub repository
- Clock: 100000000 Hz
How it works
The Mandelbrot fractal is computed "racing the beam" and displayed through the TinyVGA Pmod.
One iteration of the computation is done every clock cycle, and a maximum iteration depth of 16 iterations is used. The design is clocked at 100MHz, allowing four clock cycles per 25MHz pixel clock. This means one value is computed every 4 pixels, giving a result like this:
The computation uses 16-bit fixed point arithmetic. The multiplications are approximated to save area, giving a possible error in the least significant bit. This gives at least 14-bit accuracy on each iteration.
The output image is at a 720x480 resolution (180x480 Mandelbrot pixels).
How to test
Provide a 100MHz clock.
The image position and zoom can be configured using the input and bidir pins.
in[2:0] control the configuration to set, and {io[7:0], in[7:3]} specify a signed value when setting a register.
These values should only be updated during vsync.
| Ctrl | Value |
|---|---|
| 0 | Enable demo mode (Zooms in and out repeatedly) |
| 1 | Set X coordinate for top-left of screen to value / 2^10 |
| 2 | Set Y coordinate for top-left of screen to value / 2^11 |
| 3 | No action |
| 4 | Set X increment per column to value[9:0] / 2^13 |
| 5 | Set Y increment per column to value[9:0] / 2^13 |
| 6 | Set X increment per row to value[7:0] / 2^13 |
| 7 | Set Y increment per row to value[7:0] / 2^13 |
Note there are 180 columns and 480 rows displayed.
External hardware
Tiny VGA Pmod in the output socket.
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | Ctrl 0 | R[1] | Input 5 |
| 1 | Ctrl 1 | G[1] | Input 6 |
| 2 | Ctrl 2 | B[1] | Input 7 |
| 3 | Input 0 | vsync | Input 8 |
| 4 | Input 1 | R[0] | Input 9 |
| 5 | Input 2 | G[0] | Input 10 |
| 6 | Input 3 | B[0] | Input 11 |
| 7 | Input 4 | hsync | Input 12 |