The document compares two real-time operating systems (RTOS): VxWorks and MicroC/OS-II (UC/OS-II). VxWorks is a hard real-time, multitasking RTOS used in applications like aerospace and robotics, featuring POSIX compliance and priority-based task scheduling. In contrast, MicroC/OS-II is a simpler kernel with multitasking and priority scheduling, utilizing a message queue for inter-process communication and capable of handling nested interrupts.

1. COMPARISON OF RTOS
III YEAR EEE
EE 8691- EMBEDDED SYSTEMS
UNIT-4
K.BALAJI , AP/ECE, SSMCE

2. COMPARISON OF RTOS
VxWorks - RTOS
• VxWorks is a Hard Real Time ,
Multitasking RTOS from Wind River
Systems
• Compatible with POSIX standard Task
Scheduling
• Supports Intel-x86, ARM,MIPS,Power PC
• Kernel is called as WIND
• Supports Multicore Design
K.BALAJI , AP/ECE, SSMCE

3. VxWorks - RTOS
• APPLICATION: AEROSPACE,
DEFENSE,ROBOTICS,INDUSTRIAL
• IPC Using Queue,
sockets,Pipes,Signals
• Synchronisation using Semaphore
K.BALAJI , AP/ECE, SSMCE

4. VxWorks - RTOS
TASK CREATION & MANAGEMENT
• READY: Ready for executionn, waiting to
get CPU time
• PEND: Task in the Blocked State,
(waiting for resources)
• DELAY: Sleeping State
• SUSPEND: Used to halt a task for
Debugging
K.BALAJI , AP/ECE, SSMCE

5. VxWorks - RTOS
• TASK SCHEDULING:
– POSIX SCHEDULING FOR Process
– Wind Scheduling for Task
• Supports
– Round Robin
– Priority Based Preemption
• Interrupt Handling
– Can Handle Hardware Interrupts
K.BALAJI , AP/ECE, SSMCE

6. VxWorks - RTOS
• TASK SCHEDULING:
– POSIX SCHEDULING FOR Process
– Wind Scheduling for Task
• Supports
– Round Robin
– Priority Based Preemption
• Interrupt Handling
– Can Handle Hardware Interrupts
K.BALAJI , AP/ECE, SSMCE

7. VxWorks - RTOS
• WATCH DOG TIMER
–WdStart() Starts the Watchdog Timer when
the task is started
– Wdcancel() - to stop at any time prior to
its expiration
K.BALAJI , AP/ECE, SSMCE

8. VxWorks - RTOS
• TIMING & REFERENCE
– SIGNALRM The Timer runs with the system
timer tick and it generates the SIGNAL when it
expires
• DEVELOPMENT ENVIRONMENT
– Tornado II – IDE (Integrated Development
Environment)
– Contains Debugging & Simulator
– For Windows & UNIX
– Replaced by Eclipse Based IDE
K.BALAJI , AP/ECE, SSMCE

9. MICROC/OS-II (UC/OS-II)
• MICROC/OS-II (UC/OS-II) is a simple , easy to
use real time kernel written in C Language .
• It is a commercial RTOS from Micrium Inc
• Features:
– Multitasking
– Priority Based preemptive task scheduling
– Supports 8 Bit, 64 Bit
– Each Task is implemented as Infinite Loop
K.BALAJI , AP/ECE, SSMCE

10. MICROC/OS-II (UC/OS-II)
STATES:
1. DORMANT : Created , Present in Program
Memory but not moved to RAM
2. READY Task is in memory & waiting for CPU
turn
3. RUNNING executed by CPU
4. WAITING Temporarily Suspended
5. INTERRUPTED Enters ISR due to Interrupt
K.BALAJI , AP/ECE, SSMCE

11. MICROC/OS-II (UC/OS-II)
KERNEL INITIALISATION:
1. OSInit() :
Initialises Kernel
Creates OSIdle()- when no user task
TASK SCHEDULING
Each Task is assigned a unique priority ranging
from 0 to 63.
0- Highest Priority
K.BALAJI , AP/ECE, SSMCE

12. MICROC/OS-II (UC/OS-II)
IPC-
-Message Queue is used for exchanging single
message
- Mailbox associates a pointer to the mailbox
TIMING & REFERENCE
- OSTimeTick()- to service the clock tick interrupt
- OS_TICKS_PER_SEC should be set based on
required frequency
K.BALAJI , AP/ECE, SSMCE

13. MICROC/OS-II (UC/OS-II)
IPC-
-Message Queue is used for exchanging single
message
- Mailbox associates a pointer to the mailbox
TIMING & REFERENCE
- OSTimeTick()- to service the clock tick interrupt
- OS_TICKS_PER_SEC should be set based on
required frequency
K.BALAJI , AP/ECE, SSMCE

14. MEMORY MANAGEMENT
MEMORY IS DIVIDED INTO
SECTORS, BLOCKS
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15. • INTERRUPT HANDLING:
supports nested interrupts upto 255
• DEVELOPMENT ENVIRONMENT
• NIOS –II IDE
• ALTERA IDE
• SUPPORTS AVR,ARM,8051 CONTROLLERS
K.BALAJI , AP/ECE, SSMCE

16. PRIORITY INVERSION
• Priority Inversion is a CONDITION in
which a high Priority task needs to
wait for a low priority task to
release a resource, and a medium
priority task continue its execution.
K.BALAJI , AP/ECE, SSMCE

17. • REASON FOR PRIORITY INVERSION
• Priority Based Preemptive scheduling ensure
that a High Priority task is always executed
first.
• But Lock based Synchronisation mechanism
ensures that a process will not access a shared
resource which is currently in use by another
process.
K.BALAJI , AP/ECE, SSMCE

18. PRIORITY INHERITANCE
• Priority Inheritance is a METHOD TO AVOID
PRIORITY INVERSION PROBLEM
• In Priority Inheritance , the priority of the task
which is accessing the shared resource is
raised temporarily
• This eliminates the preemption of the low
priority task by other tasks
• The temporarily boosted priority is brought to
original value
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19. REFERENCES:
1. Raj Kamal, ‘Embedded System-Architecture,
Programming, Design’, Mc Graw Hill, 2013.
2. Dr.G.Ram Prabhu, Embedded Systems
K.BALAJI , AP/ECE, SSMCE