Windows CE is Real Time Operating system for mobile device

1. Windows CE
by:
K.Balamurugan
M.Tech-CSE-1st year

2. Introduction

3. Entertainment devices and CAR

4. What can CE do
– Industrial Automation
– Set-Top Boxes
– Medical Devices and Systems
– ATMs
– Projectors and Large Screen Displays
– VoIP Devices
– First edition released in 1996
– Windows CE .NET 4.x is widely used

5. Introduction to BSP
• Windows CE can run on different hardware
platforms.
• How can we do that?
• The answer is BSP !
• Board Support Package is the software that
implements and supports the OEM adaptation layer
(OAL) and device drivers for a standard
development board (SDB).

6. Compare with Desktop Version
– Windows XP : 1.5GB
No inherent real time
support
256 levels of thread priority
Minimal : 200KB Windows XP : 1.5GB
 Lager and lager…
 Can NOT be
customized
Quick and easy to customize OS for a
particular system
More than 200 optional component
 Compact Version of Win32 API, MFC..
 UNICODE only
 ASCII / UNICODE
 Commercial software, source code is
MS 1st level secret.
 70% of Windows CE 5.0 source code is
shared.

7. Memory Management
– Windows CE uses ROM (read only memory), RAM
(random access memory)
• The ROM in a Windows CE system is like a small read-
only hard disk
• The RAM in a Windows CE system is divided into two
areas: program memory and object store
– Windows CE is a 32-bit operating system, so it
supports 4GB virtual address space

8. Memory Management…..
– Upper 2GB is kernel space, used by the system for
its own data
– Lower 2GB is user space
• 0x42000000-0x7FFFFFFF memory is used for large
memory allocations, such as memory- mapped files
• 0x0-0x41FFFFFF memory is divided into 33 slots, each
of which is 32MB

9. Memory Management…..

10. Memory Management…..

11. Memory Management…..

12. Processes and Threads Management
– Windows CE limits 32 processes being run at any one time
– Every process at least has a primary thread associated with
it upon starting (even if it never explicitly created one)
– A process can created any number of additional threads
(only limited by available memory)
– Each thread belongs to a particular process (and shares the
same memory space)
– SetProcPermissions API will give the current thread access
to any process
– Each thread has an ID, a private stack and a set of registers

13. Processes and Threads
Management…..
– When a process is loaded
• Assigned to next available slot
• DLLs loaded into the slot
• Followed by the stack and default process heap
• After this, then executed
– When a process’ thread is scheduled
• Copied from its slot into slot 0
– This is mapped back to the original slot allocated
to the process if the process becomes inactive

14. Processes and Threads
Management…..
– Thread
– A unit of execution
– A piece of code that can be scheduled to run by the kernel
– May be launch by a process or a driver
– Process
– A collection of threads with a common execution environment
– A process has at least on thread
– Launch from an executable file
– Can create threads to handle interrupts
– Driver
– A DLL, (dynamically loaded library) loaded into the device
manager process
– Supports the Device I/O Control Interface
– Can create threads to handle interrupts

15. Processes and Threads
Management…..
– Processes allocate stack for each thread, the
default size is 64KB, depending on the link
parameter when the program is compiled
• Top 2KB used to guard against stack overflow
• Remained available for use
– Variables declared inside functions are allocated in
the stack
– Thread’s stack memory is reclaimed when it
terminates

16. Processes and Threads
Management…..

17. API Address Search

18. Scheduler
– Is responsible for determining which thread will run
– Has a queue for threads for each priority level
– Will always schedule the first thread at the highest priority level
– A thread gets to run for set length of time, called a
quantum
– Typically 100 milliseconds
– A quantum of 0 means the quantum never runs out
• The thread can run until blocked or interrupted
– A Thread runs until—
– Its quantum runs out
– It is interrupted by a higher priority thread
– Its blocked by a resource contention
• Such as access to a critical section or a mutex

19. ISRs And ISTs
– Interrupt Service Routine (ISR)
– A piece of code loaded into the kernel
– Assigned to a particular IRQ
– Called immediately to handle the hardware interrupt
– Should be written to run quickly with few outside dependencies
– Can be chained together if multiple device might use the same
IRQ
– Notifies the kernel which IST should run
– Interrupt Service Thread (IST)
– A thread registered to handle an interrupt
– Can be created by either a process or a driver
– Scheduled like any other thread on the system
– Should be written to do the bulk of the interrupt handling work

20. Priority Levels
– Windows CE 5.0 has 256 levels of priority
– Level 0 is the highest and 255 is the lowest
• The old CE model of 8 levels now map to the lowest 8
of the new model
– The default level for a thread is 252
– Levels 0 through 248 can be reserved by OEM

21. Interrupt Architecture

22. OAL Design

23. Scheduling algorithms in Windows CE

24. Scheduling algorithms in Windows CE

25. Conclusion
– Windows CE is real-time
– Windows CE provides all the functionality needed
to qualify as a real-time operating system
– Windows CE provides tools to optimize your real-
time platform