Keyboard firmware from scratch

Makerspace
,
1

I’m in the process of writing a new keyboard firmware from scratch and I was wondering if folks would be interested in following along?

The project setup is

  • chibios 20.3.x
  • arm-gcc 9.3 and above
  • CMake (no git submodules!)
  • C++17 and C11 everywhere

The firmware will be limited to ARM chips (STM32 family tbh).

I’ve got the basics all setup and am currently working on dynamic keymaps (think: via).
Eventually it’ll support hot-swapping different keyboards without any interruptions. Think combining a full-sized keyboard with a numpad or macropad, or combining different split keyboards. Anything goes.

Below is a picture of a working prototype of a corne + let’s split - it’s acting as one keyboard!

A3EF6ECA-04EB-47ED-867D-D2C4D395E141
A3EF6ECA-04EB-47ED-867D-D2C4D395E1414032×1563 2.42 MB

Let me know if you’re interested and I’d start writing some posts about what’s there and what’s coming, and how I’m going about writing a keyboard firmware from scratch.

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Why chibios over something more popular like freertos or zephyr?

3

This looks pretty cool, will the downstream keyboard be connected over proper USB so it could also be plugged into a pc and still function?

4

Great Question - I looked at Comparison of real-time operating systems - Wikipedia specifically for RTOSes which claim to have a small footprint.

Out of the 5 I picked chibios because I was most familiar with it.

I hope the page isn’t wrong, but I haven’t implemented in other RTOS to compare the footprint myself.

5

That’s probably the best reason right there.

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6

It depends on which chip you have on the pro-micro replacement PCB I think.
Right now I’m using STM32G031/PCA9675 for prototyping. For those the answer is no. But if you develop a drop in replacement with a chip which actually has USB support the answer would be yes.

The current setup is a 3 component Y-splitter setup, where you only plug the Y splitter into your PC, and the keyboards into the Y-splitter. The firmware runs on the Y-splitter, performing all keyboard actions.
Y-Splitter communication runs on the TX/RX lines of the 3.1 USB-C cable.

So I guess the answer is yes, but I’ve not gone there (yet).

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7

That’s actually a really smart way to do that that gets you around needing an MCU with a USB host interface!

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