stmos

stmos is an attempt to implement a general-purpose operating system on ARM microcontrollers. The name "stmos" is due to the fact that this was first implemented on an STM32L476RG MCU (ARM Cortex-M4F), and the operating system still includes many operations/values that are specific to this processor (currently limiting the portability of this OS).

Eventually, this OS aims to support at least all Cortex-M MCUs.

Features:

• Advanced heap that does its best to keep large chunks of memory available
• Round-robin multitasking that keeps tasks in userspace
• A virtual filesystem implementation with stdio/initrd built into the kernel
• Ability to execute ELF files loaded from the filesystem
• A nearly complete C standard library implementation available to loaded ELFs (using PDCLib)
• libgpio: The first userspace library; makes GPIO available to loaded ELFs

Currently supported processors:

• STM32L476RG (board: NUCLEO-L476RG)

building

To build stmos, you'll need the following programs:

• The arm-stmos toolchain (see the arm-stmos folder)
• openocd
• gdb (with multiarch support, gdb-multiarch on Debian)

To compile stmos simply run make (-j supported). To upload, use run.sh to launch OpenOCD and GDB; then, do lo to load stmos, and c to begin execution.

notes

Currently, the only available filesystem driver is for the initrd. Files in the folder src/initrd/files are put into the initrd. C source files in src/initrd are compiled (with libgpio available), placing the programs in src/initrd/files

What's next for stmos?

• Processor independence
• SD card support?
• Display support? (ILI....)
• Support for running a popular program (e.g. a shell like sash, maybe lua)
• Growth of features available to loaded ELFs (better execve, signals?, etc.)