ergodox-compress-keymap

Reduce firmware size for Glow keyboards

The memory on the ErgoDox EZ is limited, especially if you enable animations or the debugging console. Looking at a keymap generated by Oryx shows quite some waste:

• The ledmap is stored wastefully with gaps between layers. So if you have 10 layers and lighting defined for the last only, you still pay the storage for all layers.

const uint8_t PROGMEM ledmap[][DRIVER_LED_TOTAL][3] = {
    [1] = { ...

You can alleviate it a bit by moving all lit layers to the beginning, the ones at the end will not allocate storage.

• Most of the time only a few keys are lit, yet colors for all keys are stored, most of them black.

    [1] = { {0,0,0}, {0,0,0}, {0,0,0}, {0,0,0}, {0,0,0},

• Most people use only a few distinct colors, yet the coding assumes all 16581375 colors are used, storing 8-bit RGB.

This script rewrites a keymap.c file as downloaded from Oryx in the following ways:

• Add a table with all distinct color definitions used by the map.

• For each lit layer, generate an array of (index, color) [2 byte] tuples coding lit keys only (color is an index into the table above)

• Therefore, each lit key will only use 2b (plus some small overhead for the global tables)

• I managed to save 622 bytes on a map with 7 lit layers

The same can probably been done for the keymaps itself.

Bit coding could improve compression further ;)

Usage

Adjust KEYMAP_FILE at the top of ergodox_compress_keymap.py. That file will be overwritten with the new version! Then run the script to get a compressed keymap.c.

Also see build.sh for an example build script that automates all this (needs adjustment of paths to your setup).