#arm #cortex-m #smartwatch

no-std app mwatch-kernel-stm32l4

A embedded 'Smart' watch

1 stable release

2.0.0 Dec 23, 2022

#1624 in Embedded development


2.5K SLoC

Build Status


An embedded smartwatch written with Rust, using the RTFM framework for multithreading.



  • Capacitive touch sense inputs - with support for multitouch gestures
  • Full 16bit colour ssd1351 OLED
  • Runtime installable apps (see SDK section for more info)
  • Real time clock
  • Notification alerts via bluetooth
  • Buildable on stable rust 2018

Developing applications for the MWatch

The mwatch provides an SDK for developing applications that can be installed at runtime via the mwatch-send-tool. More info about the SDK can be found in the SDK repo.

System Architecture


The MWatch tries to follow a modern computer operating system, complete with a kernel, a built in window/display manager along with a user space api for developing user space apps on the watch, as well as some builtin applications.

Window/Display Manager

The window manager handles input and rendering of states/applications inside the watch, all states must implement the State trait to run but can optionally implement other helper traits which allows the window manager to enable more functionality for a state.

Kernel API

The kernel among otherthings provides an API for the sdk to interact with, this is providided by lib.rs in the kernel crate. This allows the SDK to properly depend on the kernel, meaning if the kernel implements a new API all that is required for the sdk to use it is to bump the version of the kernel. Currently there is no checking done on the binary the sdk produces to make sure it is compatible with the current running kernel.


The MWatch has a builtin bluetooth module connected to usart2. Through this serial interface we can recieve Notifications, Applications and more. The basic procotol looks like this

                Can repeat many times based on the type 

In english, start byte followed by a type followed by any amount of delimiters followed by data finally ETX. All data must be valid ascii, to send binary data you must convert to hex nibbles first. See the application_manager for more info.

Input management

The TSC (touch sense controller) builtin to the mwatch provides three inputs. The kernel polls these inputs and multiplexes there results to produce a final output. For example touching the middle button produces a middle output, touching the left and right at the same time produces a dual-click output.




  • Requires the thumbv7em-none-eabi target to be installed, use rustup target add thumbv7em-none-eabi to do so.
  • Requires cargo-binutils for extra features, such as generating a stripped binary. Note: The llvm-tools-preview component must be installed with rustup component add llvm-tools-preview for it to work.


Licensed under either of

at your option.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

Copyright Scott Mabin 2019


~1.5M SLoC