Why OS

• Why: OS Documentation

Course Structure

• OS Primitives: Overview
  • Interrupts
  • Spinlocks
  • Schedulable Context (Threads)
  • Polling
  • Optional
    • Deadlock Scenarios
    • Random Stuff
• OS Primitives: Interrupt Handling
  • IRQs And ISRs
• OS Primitives: Spinlocks
  • Producer/Consumer Interrupts
  • Problem: Interrupt Parallelism
  • Solution: Spinlock
• OS Primitives: Threads
  • Threads Basics
  • Main Thread
  • jjj Handler Threads

Todo

• Restructure why/code -> why/why-os

  • rename cmake targets accordingly

• Reformulate Tasks? Processes? Threads? in terms of this

• Enable/disable safeguards against blocking in interrupts

  • class FD to handle this

  • start unchecked

    • inside the isr, prompt the user

    • see how everything stalls

    • user input -> continue

  • enable check

Random Notes

jjj sort that out

Intro

When you somewhere want to consume data that was produced by an ISR, you either do it in another (timer possibly) interrupt, or in the main loop, pointlessly polling for something that will only happen once in a lifetime. must do powermanagement in that loop, suspending the device in deep sleep when on battery.

• show isr race condition on a list for example jjj link to source

• show fix via spinlock (show why-spinlock.cpp)

• Discussion: do much in ISR -> write program that has a global std::list, and adds/removes one node in each isr

  https://codeberg.org/jfasch/jf-why-rtos/src/branch/main/firmware/do-much-in-isr.cpp

• Some memory model

• Add spinlock

  https://codeberg.org/jfasch/jf-why-rtos/src/branch/main/firmware/do-much-in-isr-spinlock.cpp

• Add why-shell

Scheduling, Tasks/Threads

Realtime

• hmmm show priority inversion?

Interrupt Communication

• message queue/pipe usage -> blocking in isr forbidden

• possibly only signal someone who’s sleeping?

• one msqg for (thread, interrupt)? or msgq1=(thread1, (interrupt1, interrupt2)), msgq2=(thread2, (interrupt3))

Polling