RTOS

• RTOS means Beal-Time Operating System.
• Special OS used in embedded systems for deterministic (time-critical) operations.
• Required in systems where multiple things/executions happen together like sensor data reading, motor controlling, communication with other peripherals.

Abbreviations

• PCB – Process Control Block.
• TCB – Task Control Block.
• RTOS – Real Time Operating System
• GPOS – General Purpose Operating System
• OS _ Operating System

RTOS Vs GPOS

• GPOS for Gentral Purpose Usage like Windows, Linux, Android, Apple IOS.
• RTOS are Like FreeRTOS, VxWorks, QNX, INTEGRITY

Different RTOS:

• FreeRTOS from FreeRTOS.rg
• VxWorks from
• embOS from SEGGER
• uC-OS

Scheduler

• Decides which task/Threads should run at time with respective to which priority.

What is Task/Threads?

• Its small independent units of execution.

Task States

• Ready
• Running
• Blocked
• Suspended

What is Preemptive Scheduling?

• Higher priority task can interrupt a lower priority task.

Cooperative Scheduling?

• Task must voluntarily yield CPU. Simpler, but if one task never yields, system can hang.
  

Context Switching?

• A context switch is a procedure that a computer’s CPU (central processing unit) follows to change from one task (or process) to another while ensuring that the tasks do not conflict. Effective context switching is critical if a computer is to provide user-friendly multitasking.
• Switching the CPU to another process requires saving the state of the old process and loading the saved state for the new process.

What are the different interprocess communications?

• Queue – FIFO structure for sending data between tasks.
• Mail Box – Like queue, but stores only one message at a time.
• Semaphore
  • Counting Semaphore: Control access to limited resources (e.g., 3 UART channels).
  • Binary Semaphore: Acts like a signal (e.g., ISR signals a task).
• Mutex – Protects shared resource (e.g., one task at a time writes to EEPROM). Has priority inheritance to avoid priority inversion.
• Message passing (MAIL BOX),
• Shared a memory,
• Socket connections.

Dead Lock

• Two or more tasks wait forever for each other’s resources.

Priority Inversion

• High-priority task blocked by low-priority task holding resource

Priority Inheritance

• Temporarily boost low-priority task.

More

• TMS570LC4357 FreeRTOS on Launchpad
• ESP32 Lua RTOS