What is Xinu?

Xinu stands for Xinu Is Not Unix -- although it shares concepts and even names with Unix, the internal design differs completely. Xinu is a small, elegant operating system that supports dynamic process creation, dynamic memory allocation, network communication, local and remote file systems, a shell, and device-independent I/O functions. The small size makes Xinu suitable for embedded environments.

What is Xinu for STM32

Xinu for STM32 is a port of the ARM version of Xinu. The STM32 family of 32-bit microcontrollers is a popular SoC based on the Arm Cortex-M processor. Besides porting the original version, Xinu for STM32 is extended with the following specific Cortex-M* features:

• Shadowed Stack Pointer: Two stack pointers are available. The MSP is used for the OS Kernel and interrupt handlers. The PSP is used by application tasks.
• PendSV exception for scheduling: If Xinu decides that context switching is needed, it sets the pending status of the PendSV, and delays the context-switching request until all other IRQ handlers have completed their processing before carrying out the PendSV exception

Supported Peripherals (currently)

• UART (Serial)
• GPIO
• SPI

Tested boards

1. STM32F103* - https://stm32-base.org/boards/STM32F103RCT6-STM32-Mini-V2.0
2. Qemu for STM32 - https://github.com/beckus/qemu_stm32

How to build and run

Xinu for STM32 uses simple Makefiles. The source code should be compiled with a cross compiler (i.e. Ubuntu's standard package: GCC cross compiler for ARM Cortex-A/R/M processors) STM32Flash (https://sourceforge.net/projects/stm32flash) can be used for flashing the compiled code to the device's flash ROM. Use qemu make to run Xinu for STM32 in Qemu. Please note that this version of qemu should be manually build (see https://github.com/beckus/qemu_stm32)

Screenshots

More general information about Xinu can be found at https://xinu.cs.purdue.edu/