Xinu OS for AVR atmega328p (Arduino)

What is Xinu?

Xinu stands for Xinu Is Not Unix --

Xinu is a small, elegant, and easy to understand complete operating system, originally developed by Douglas Comer for instructional purposes at Purdue University in the 1980s.

Xinu supports dynamic process creation, dynamic memory allocation, network communication, local and remote file systems, a shell, and device-independent I/O functions. Since the whole source code size is small, Xinu is suitable for embedded systems.

Xinu arranges the components of the system into a hiearchy of layers, clarifying the interaction between the various components of the system and making the system easier to understand and modify. Despite its small size, Xinu uses powerful
primitives to provide the same functionality many con- ventional operating systems supply.

Xinu originally ran on Digital Equipment Corporation LSI 11's with only 64K bytes of memory, at the end of 1979 and the inning of 1980. Over the years Xinu versions Xinu have been expanded and ported to a wide variety of architectures and platforms, including: IBM PC, Macintosh, Digital Equipment Corporation VAX and DECStation 3100, Sun Microsystems Sun 2, Sun 3 and Sparcstations, and for several ARM, MIPS and x86 embedded boards. It has been used as the basis for many research projects. Furthermore, Xinu has been used as an embedded system in products by companies such as Motorola, Mitsubishi, Hewlett-Packard, and Lexmark. There is a full TCP/IP stack, and even the original version of Xinu (for the PDP-11) supported arbitrary processes and network I/O. have been ported

There are current versions of Xinu for Galileo Intel boards, ARM Beagle Boards, several MIPS platforms, and for x86 PC hardware and virtual machines.

Many sites defines Xinu as a free Unix system, or similar statements. It is not. Xinu differs completely from the internal structure of Unix (or Linux). For academic purposes Xinu is smaller, elegant, and easier to understand. Applications written for one system will not run on the other without modification. Xinu is not Unix.

Xinu OS for AVR atmega328p

This version of Xinu runs on AVR atmega328 microcontroller, which just provides 2KB of RAM, 32KB of Flash memory and 1KB of EEPROM. This port of Xinu uses 17KB of FLASH and 0.9KB of RAM, so there are still resources (SRAM and FLASH) available for developing an embedded system solution programming concurrent processes under a real operating system; using for example, an Arduino hardware and the Xinu operating system inside.

Xinu is easy of understand, so a developer can obtain a copy of the system to examine, modify, instrument, measure, extend, or transport it to another architecture.

Douglas Comer

Douglas Comer is a Professor of Computer Science at Purdue University who was inducted into the Internet Hall of Fame on September, 2019.

https://www.cs.purdue.edu/homes/comer/ https://www.cs.purdue.edu/news/articles/2019/comer_ihof.html

As one of the earliest TCP/IP and internetworking researchers, Comer wrote the first series of textbooks explaining the scientific principles underlying the design of the Internet and its communications protocols, providing some of the earliest formal guidance for building efficient networks and applications that use the Internet.

Comer’s three-volume textbook series, Internetworking with TCP/IP, written in 1987, is widely considered to be the authoritative reference for Internet protocols. The series played a key role in popularizing Internet protocols by making them more understandable to a new generation of engineers and IT professionals.

Version 6 Xinu, as it was called, supplied primitives to handle memory manage- ment, process management, process coordination/synchronization, interprocess communication, real-time clock management, device drivers, and intermachine communication (a ring network). Version 7 Xinu replaced the

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/