User's manual

Last modified on Sat Jul 22 11:30:02 2023 UTC.

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Note: The User’s Manual is currently work in progress.

RTOS

Getting started with µOS++

• Overview
  • Multiple APIs
• The os_main() and the main thread
• Multiple thread applications

Basic concepts

• Soft vs hard real-time systems
• Superloop (foreground/background) applications
• Multi-tasking
  • Tasks
  • Why multiple threads?
  • Threads & processes
  • Blocking I/O
  • The idle thread
  • Sleep modes and power savings
  • Context switching
  • Thread stacks
  • Cooperative vs preemptive multi-tasking
  • Thread interruption/cancellation
• Scheduling
  • Thread states
  • The READY list
  • Scheduling algorithms
  • Round-robin vs priority scheduling
  • Selecting thread priorities
  • Priority inversion / priority inheritance
• Communicating between threads and/or ISRs
  • Periodic polling vs event waiting
  • Passing messages
  • Event flags
  • Semaphores
• Managing common resources
  • Disable/enable interrupts
  • Lock/unlock the scheduler
  • Counting semaphores
  • Mutual exclusion (mutex)
  • Should a semaphore or a mutex be used?
  • Deadlock (or deadly embrace)
• Statically vs. dynamically allocated objects
  • The system allocator
  • Fragmentation
• Real-time clock
• Terms to use with caution
  • Kernel
  • Tasks vs threads

Features

Threads

• Overview
• Thread functions
• Thread priorities
• Creating threads
• Changing thread priorities
• Other thread functions
• Destroying threads
• The current thread
• Thread states
• The thread stack
• The idle thread
• The main thread

Thread event flags

• Overview
• Raising thread event flags
• Waiting for thread event flags
• Other thread event flags functions

Semaphores

• Overview
• Semaphore types
  • Binary semaphores
  • Counting semaphores
• Creating semaphores
• Posting to semaphores
  • Posting to semaphores from ISRs
• Waiting on semaphores
• Multiple threads waiting on a semaphore
• Other semaphore functions
  • Getting the semaphore name
  • Getting the semaphore value
  • Getting the semaphore maximum value
  • Getting the semaphore initial value
• Destroying semaphores
• Using semaphores for resource management
• Unilateral rendezvous
• Semaphore pitfalls
  • Unbalanced wait()/post()
  • Recursive deadlock
  • Thread-termination deadlock
  • Priority inversion
  • Wrong initialisation

Event flags

• Overview
• Creating event flags
• Raising event flags
  • Raising event flags from ISRs
• Waiting for event flags
• Multiple threads waiting on event flags
• Other event flags functions
  • Getting the event flags name
  • Getting individual flags
  • Clearing individual flags
• Destroying event flags

Mutexes

• Overview
  • Normal mutexes
  • Recursive mutexes
• Creating mutexes
• Acquiring a mutex
• Releasing a mutex
• Multiple threads waiting on a mutex
• Other mutex functions
• Destroying mutexes
• Priority inversion
• Priority inheritance
• Deadlock (or deadly embrace)

Condition variables

• Overview
• TODO

Message queues

• Overview
• Queue storage
• Message priorities
• Creating queues
• Sending messages to queues
  • Sending messages from ISRs
• Receiving messages from queues
• Other message queue functions
• Multiple threads waiting on message queues
• Destroying queues

Fixed size memory pools

• Overview
• Pool storage
• Creating memory pools
• Getting a memory block
  • Getting a memory block from ISRs
• Returning a memory block
• Other memory pools functions
• Multiple threads waiting on memory pools
• Destroying memory pools

Software timers

• Overview
• Timer functions
• Creating timers
• Start a timer
• Stop a timer
• Other timer functions
• Destroying timers

Clocks

• Overview
• The system clock
• The real time clock
• The high resolution clock

Interrupts & critical sections

• Overview
• High/low priority interrupts
• Interrupt nesting
• Critical sections
• Uncritical sections

Memory allocators

• TODO

The scheduler

• Scheduling points
• The ready list
• The scheduling algorithm
• Waiting lists
• The idle thread

Run-time statistics

• Per-thread number of context switches
• Per-thread number of CPU clocks used

Iterating threads

Credits

As the saying goes, “Books are written from books, and software from software”. As such, this manual too did not appear from nothing, but was influenced by the following manuals:

• “Using the FreeRTOS Real Time Kernel”, by Richard Barry
• “µC/OC-III The Real-Time Kernel - User’s Manual”, by Micriµm
• “embOS & embOS-MPU - Real-Time Operating System - CPU-independent - User & Reference Guide”, by SEGGER

Other links:

• The Feabhas Blog

Many thanks for their impressive work and for providing the inspiration.

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