1. Semaphores
-Gajendra Singh

2. SHARED DATA PROBLEM

4. ATOMIC or CRITICAL SECTION

8. Interrupt Latency
The longest period of time during which that interrupt is disabled
Task code1 :disable interrupt for 125uS.
Task code2 :disable interrupt for 250uS.
Task code3 :critical & need to respond within 625us.
Interprocessor interrupt routine takes 300uS to execute.

9. Points to be noted
Lets cut the cost and replace uP that runs half as fast.
Similarly adding an extra task might also be awful.
Conclusion: Disabling Interrupts “Not a very good idea.”

10. Architectures Round Robin Round Robin with Interrupts
Function Queue Scheduling
RTOS

11. ISR_A;
ISR_B; :
ISR_Z
main(){
while(1){
if(A){ // do something}
if(B){// do something}
if(Z){// do something} }

12. Tasks And Data

13. Shared data Problem with OS

14. Have a Look:

15. Reentrancy
Reentrant Functions: can be called by more than one task and still work correctly even if RTOS switches from one task to another in middle of executing one function.

16. Gray Areas:

17. For 8051
For INTEL 80x86

18. Semaphores

19. Initializing Semaphores

21. Advantages
Multiple Semaphores.
As signaling Device

23. DeadLock