266 VGA Mandelbrot
266 : VGA Mandelbrot
- Author: Mike Bell
- Description: Mandelbrot on VGA, racing the beam
- GitHub repository
- Open in 3D viewer
- 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 over two clock cycles, and a maximum iteration depth of 14 iterations is used. The design is clocked at 100MHz, allowing four clock cycles per 25MHz pixel clock. This means one value is computed every 7 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 (~103x480 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 103 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 |