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