HUB75 display drivers and demos

This project contains drivers for one or more daisy-chained HUB75-based LED matrix displays, for the Propeller 1 chip, along with demo/test programs.

The fastest of the display drivers uses the cog video hardware to shift the display bits out at sysclk/4 (20 MHz for an 80 MHz system clock), but it is the hardest version to understand. The other versions are forms of bit-banging, but may be clearer. The drivers also include routines (in both Spin and PASM) for writing individual pixels, horizontal and vertical lines, boxes, one-bit bitmaps, and ROM font characters to the display buffer.

The demo and test programs exercise many of the write routines, report driver performance, and illustrate some aggressive ways to maximize hub memory buffer size for the display buffer. Another demo program is a digital clock with controls for many digit change animations, digit color and intensity, using ROM font digits. In addition, they show an approach to aggressive hub memory "recovery" to maximize the size of the hub display buffer.

One final demo is a "gamma explorer" that shows the effects of gamma adjustments for LED intensity for various bit depths, and shows how to use the ROM log and antilog tables with interpolation to increase accuracy.

For one 64x64 display, the fastest driver can do 64.6 refreshes per second for 7 bits per color (21-bit color, 7:7:7) with an 80 MHz clock.