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Repo Description:

  • Custom RTOS for STM32 Blue Pill using Custom Device Drivers, No Third Party Libraries like HAL or CMSIS
  • This Repo has been structured in such a way that with each version, we can see the improvements/features added instead of a single project which has the latest version of code only, for learning purposes.

Intro:

  • For now the scheduler currently implemented is a Round Robin Scheduler with Cooperative Scheduling.
  • A fixed priority pre-emptive periodic scheduler will be added in later.

Versions:

  • Versions 1-4 all use MSP & SysTick Handler only
  • PSP & PendSV Handler functionality will be introduced in the next few versions

Round Robin v1:

  • simplest form of Round Robin Scheduler
  • use MSP only for both Kernel and Tasks
  • Task only has,
    • A Pointer to the Task Function
  • TCBs as a circular linked list
  • On Context Switch, the next node (task) is selected

Round Robin v2:

  • Added Task Yield for Cooperative Scheduling
  • Added Description to Task
  • Bringing Task related code into Task source from Kernel source
  • Refining Stack Init by adding Task Stack Init and Task Init APIs
  • Added Macro for global IRQ Disabling and Enabling
  • Added Periodic Tasks but removed it later in this version
  • Added Round Robin Scheduler API
  • Modified Systick Handler to call the scheduler API
  • Added RTOS Info
  • Added Config for Scheduler type
  • Updated Serialprint

Round Robin v3:

  • Introduce Semaphores,
    • Init
    • Give
    • Take
    • Cooperative Take
  • Updated Serialprint and done the same to previous versions
  • Added Idle Task & Task Delay
  • Added Assert
  • Modified Round Robin Scheduler to account for the Idle Task and Task Delay Functionality

Round Robin v4:

  • Introduce Weighted Round Robin Scheduler API
  • Added for tasks,
    • Weighted Task Add API
    • Task Reset Quota API
  • Added RTOS Scheduler Init API
  • Refine RTOS Info

Structure:

  • Systick is initialized based on the Task Quanta (in milliseconds) defined in Round Robin Scheduler

Config:

  • Settings for the RTOS

Kernel:

  • Main part of the RTOS
  • Handles,
    • Initializing TCB's, their stack, the Scheduler
    • Starting/Launching the Scheduler
    • Determining the next task to run
    • Context Switch to the next task

Tasks:

  • Defines the TCB Structure
  • API's related to tasks
    • Adding a task
    • Defining a Idle Task
    • Task Yield
    • Task Delay
    • Task Unblock
  • TCBs as circular linked list
  • TCBs' stack as an array

RTOS Info:

  • provides the necessary info about the tasks and the scheduler before the scheduler starts

RTOS Port:

  • contains the Device Driver Headers
  • custom, no HAL or CMSIS

Semaphore

  • Semaphore Definitions which can be used in the tasks