This repository keeps the source code of a Xinu operating system version designed to run on an AVR atmega328p microcontroller.
Using just the major pieces of this Xinu repository (and any bare AVR MCU or Arduino board) it is possible to develop a multi tasking embedded system.
A complete application example is provided as well: the Xinu shell for user interface, and several programs and UNIX-like utilities.
Check the video (an Arduino board running the Xinu shell and several concurrent processes, under the control of Xinu).
## What is Xinu?
Thus the source code is comprise of:
Xinu is a small, elegant, and easy to understand operating system, originally developed by Douglas Comer for instructional purposes at Purdue University in the 1980s.
1. The **Xinu OS** for AVR atmega328p (microkernel)
2. Basic examples (**apps**) of how to use Xinu
3. A complete example: **The Xinu shell** and ultra tiny versions of several **UNIX-like utilities** for AVR atmega328p (it includes an editor, a basic interpreter, ps, kill, free, and several more)
The Xinu Operating System includes: dynamic process creation, dynamic memory allocation, real-time clock management, process coordination and synchronization, local and remote file systems, a shell, and device-independent I/O functions.
<aname="whatisxinu">
### <aname="whatisxinu"></a>What is Xinu?
Xinu is a small, elegant, and easy to understand operating system, originally developed by Douglas Comer for instructional purposes at Purdue University in the 1980s.
<strong>The Xinu Operating System includes</strong>: dynamic process creation, dynamic memory allocation, real-time clock management, process coordination and synchronization, local and remote file systems, a shell, and device-independent I/O functions.
Xinu uses powerful primitives to provides all the componentes and the same functionality many conventional operating sytems supply. Since the whole source code size is small, Xinu is suitable for embedded systems.
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.
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**.
## History
### History
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.
There are current versions of Xinu for Galileo Intel boards, ARM Beagle Boards, several MIPS platforms, and for x86 PC hardware and virtual machines.
## Xinu OS for AVR atmega328p
Current Xinu versions are designed for ARM, MIPS and x86 architectures . The hardware differences between those and the ultra small AVR microcontroller required substantial changes to some low-level structure of Xinu, mainly using the FLASH memory in the AVR MCU for keeping several read only data structures previously
in RAM.
The Xinu version for AVR atmega328p has the core functionality of Xinu, and provides some extensions, including an eeprom file system and several UNIX like utilities for the Xinu shell.
### Xinu OS for AVR atmega328p
Current official Xinu versions are designed for ARM, MIPS and x86 architectures . The hardware differences between those and the ultra small AVR microcontroller required some changes to some low-level data structures of Xinu, mainly using the FLASH memory in the AVR MCU, for keeping several read only data structures, previously in RAM. Also, several limits were imposed so those data structures fits into the SRAM AVR memory. The Xinu version for AVR atmega328p has the core functionality of Xinu, and provides some extensions, including an eeprom file system and several UNIX like utilities for the Xinu shell.
This MCU has just 2KB of SRAM, 32KB of FLASH memory, and 1KB of EEPROM. The Xinu version for AVR fits in 17KB of FLASH and 0.9KB of RAM, so there are still room (SRAM and FLASH) available for the developing of an embedded system, using a real operating system and an inexpensive hardware (like bare MCUs or any board of the tons of Arduinos that you will find around).
This MCU has just 2KB of SRAM, 32KB of FLASH memory, and 1KB of EEPROM. The Xinu version for AVR uses 17KB of FLASH and 0.9KB of RAM, so there is still room (SRAM and FLASH) for the embedded application running on Xinu (concurrent processes).
So this project might be stimulating and very fun for lovers of embedded systems development and operating system internals.
Most of the Xinu kernel has been ported in this work in progress.
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.
Notes about the port:
1. Max. number of processes (4 to 8)
2. main process is now the embedded application process
3. Max. number of semaphores (2 to 6) (the size of the table of process queues depends on this)
4. Max. number of devices (4 to 5)
4. The preemption reschedules a new process for CPU every 300ms
5. Several limits for buffers: 32bytes for tty input, 16bytes for names of devices, 1byte for the queues keys, and the list continues.
## Douglas Comer
### 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.
@ -55,3 +57,7 @@ As one of the earliest TCP/IP and internetworking researchers, Comer wrote the f
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.
### Getting started
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.
Rafael Zurita
6 years ago