Reasons To Prefer An Operating System Over Bare Metal

Conceived as a series of demos, live-programmed by the trainer, this course gives

• An understanding of the problems solved by operating systems

• An overview of the building blocks that any operating system brings

  • Tasks and multitasking

  • Scheduling multiple tasks, in the presence of task priorities

  • Synchronization and communication primitives like mutexes, semaphores and message queues

• An introduction to event driven programming, a technique to simultaneously react on multiple events withing a single task [1]

Course Flow

Interrupt Madness

• Overview: Terminology

• The Thing To Control

• Excursion: WhyOS Interrupt Handling

• Firmware: Initial Version (Driven By Interrupts)

• Firmware: Fixing Interrupt Concurrency Bugs (Spinlock)

• Excursion: More About Spinlocks

• Hardware: CAN Controller JF0815

• Firmware: Emit CAN “State Change Notification” Frames

Summary

• Firmware: Not So Well Anymore

Basic OS Building Blocks

• Threads: Scheduling, Blocking, And Realtime

• Semaphores: At The Basis Of Waiting

• Message Queues: Easy Communication

Getting Rid Of Long-Running Interrupt Service Routines

• (TODO) Sketch/Plan: CAN into thread/mq; 3 more threads (one for each ISR)

• Device Driver: CAN Controller JF0815

• Firmware: Dedicated Thread For CAN Transmission

• Firmware: Dedicated Thread For Timer Tick

• Firmware: Dedicated Thread For “Sensor Burning” Event

• Firmware: Dedicated Thread For “Operator Button” Event

• (TODO) Replace Spinlock with Mutex. Talk about priorities. Add different ones (mentioning Zephyr does not support fair scheduling). Talk about priority inversion and inheritance.

Advanced: Event Multiplexing

• Firmware: Collapse Three Threads Into One (Eventloop)

• (TODO) Add watchdog feeder?

Additional Material

OS Primitives

• Overview: Terminology
• Interrupt Handling
• Spinlocks
• Threads: Scheduling, Blocking, And Realtime
• Message Queues: Easy Communication
• Semaphores: At The Basis Of Waiting
• Timers, And Timer Callbacks
• Polling: Event Driven Programming

Futher Reads

• WhyOS: Documentation

• The C++ Memory Model

Demo Project: Nuclear Power Plant Controller

• Controlling Critical Things: A Semi-Realistic Project

Demo Project: Datalogger

• Datalogger: A Semi-Realistic Project (Threaded Version)
• Datalogger: A Semi-Realistic Project (Events Version)

Footnotes

[1]

This technique is mostly known from the Linux and Zephyr operating systems