Areas of RTOS

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RTOS concepts
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Why RTOS
Classification of RTOS
- hard real time
 - firm real time
- soft real time

RTOS Architecture

1. Kernel
• what does it do?
• process - ready, running, blocked, suspended (Scheduler)
• process priority
• process communication
• memory management
• provide interfaces for UserSpace applications
• interrupt and event handling
• device io and device driver
• file system
• POSIX
• kernel Types
• monolithic (Most OS like Ubuntu kernel)
• microkernel (Most RTOS like QNX)
• exokernel
2. Scheduler
• First in first out
• Earliest deadline first
• Pre-emptive (Fixed priority)
• Round robin
3. Task
• states - Ready, running, Blocked, Suspended
• Task control block (ID, Priority, Status, register, PC, SP)
• priority of task
• task implementation - creation, deletion, suspend, resume
• idle task
4. Co-routines
• states - ready, Running, Blocked
5. Task synchronization
• Binary semaphore
• Counting semaphore
• Mutex (Mutually Exclusion Semaphores)
• Priority Inversion problem
• Solution - 
• Priority Inheritance
• Priority ceiling
• Recursive mutex
• Task notifications
6. Intertestk communication
• Messgae queues (structured data exchnage )
• Mailbox - messgae queue with length 1
• 
  
• Pipes (unstructured data exchange - byte stream)
• Remote procedure calls (RPC) - one task initiating another task on remote computer. XMLRPC is a kind of RPC as used in project
7. Memory Management
• Stack management
• Heap management
8. Timer Management
• Ticks counting used for task delay
• Task alert
9. Interrupt and Event Handling
• defining Interrupt handler
• creation and deletion of ISR
• Enabling and disabling ISR
• changing and referencing of interrupt mask
10. Device I/O Management
• Provide APIs of using device drivers
11. Selection of RTOS
• Technical consideration
• Scalability
• Portability
• Run-time facilities
• Development tools
• Commercial Considerations
• Costs
• License
• Supplier stability/ longevity
• Usually there are no thread concepts in RTOS. Task are the only things.