Optimizing Windows ® CE For Real-Time Systems Paul Yao President The Paul Yao Company

Agenda Introductions (5 minutes) Introductions (5 minutes) Terms (5 minutes) Terms (5 minutes) RT-features of Windows CE (15 minutes) RT-features of Windows CE (15 minutes) RT enhancements for Windows CE 3.0 (15 minutes) RT enhancements for Windows CE 3.0 (15 minutes) Optimization tips (20 minutes) Optimization tips (20 minutes) Discussion (15 minutes) Discussion (15 minutes)

Terms Real time – A system in which specific data collection or device control must be handled within specified time parameters Real time – A system in which specific data collection or device control must be handled within specified time parameters  1 Millisecond (1 ms) =.001 second  1 Microsecond (1 ms) = second Hard real time – Catastrophic results for failure to meet time-critical needs Hard real time – Catastrophic results for failure to meet time-critical needs Soft real time – Non-catastrophic results Soft real time – Non-catastrophic results

CE Kernel Features Multi-process operating system (32 max) Multi-process operating system (32 max) Multi-threaded Multi-threaded  256 thread priorities (new with Windows CE 3.0) Synchronization Synchronization  Critical sections  Mutexes  Semaphores (new with Windows CE 3.0)  Events Memory Memory  Paged  No backing store

Interrupt Handling Event NK.EXE IRQ User Mode Kernel Mode ISR = “Interrupt Service Routine” IST = “Interrupt Service Thread” A B C Event

Windows CE 3.0 Real-Time Features Better interrupt handling Better interrupt handling  Support for nested interrupts  Improved interrupt latencies Better control of Scheduler Better control of Scheduler  More thread priorities  Control of time-slice quantum  Restrictions based on Trust  Better synchronization support  Higher timer resolution  Better priority inversion handling

Nested Interrupts Windows CE 2.x Windows CE 2.x  No nesting  IRQs always run to completion  ISTs run to completion when created with highest priority Windows CE 3.0 Windows CE 3.0  Nesting supported  IRQs can be interrupted  Registers saved and restored  Interrupts only occur for higher priority IRQs

Interrupt Latency Event NK.EXE IRQ User Mode Kernel Mode ISR = “Interrupt Service Routine” IST = “Interrupt Service Thread” A B Event

Thread Priorities Windows CE 2.x Windows CE 2.x  Eight priorities – 0 to 8  SetThreadPriority(hThread, nPriority) Windows CE 3.0 Windows CE 3.0  256 priorities – 0 (real-time) to 255  CeSetThreadPriority(hThread, nPriority)

New Thread Priorities Windows CE 2.x SetThreadPriority() Windows CE 2.x SetThreadPriority()  0 = real-time  1  2  3 = normal  4  5  6  7 = idle-time Windows CE 3.0 CeSetThreadPriority() Windows CE 3.0 CeSetThreadPriority()  0 (RT) to 247  248  249  250  251  252  253  255

Thread Quantum Control Quantum = Duration of time slice Quantum = Duration of time slice Platform builder – Set default Platform builder – Set default  During call to OEMInit()  Set dwDefaultThreadQuantum Individual threads: Individual threads:  DWORD CeGetThreadQuantum();  BOOL CeSetThreadQuantum (DWORD dwTime)

Thread Quantum Examples // Set quantum to 100 ms. CeSetThreadQuantum(100); // Set quantum to 500 ms. CeSetThreadQuantum(500); // Set run to completion. CeSetThreadQuantum(0);

Certifying Trust Untrusted applications: Untrusted applications:  Cannot call CeSetThreadPriority  Cannot call CeSetThreadQuantum Platform Builder – OEMCertifyModule Platform Builder – OEMCertifyModule Checking Trust: Checking Trust:  DWORD CeGetCurrentTrust(void);  DWORD CeGetCallerTrust(void);  0 = None, 1 = Some, 2 = All

Synchronization Enhancements TryEnterCriticalSection() – TryEnterCriticalSection() –  Non-blocking call Semaphores Semaphores  A “mutex with a count”

Timers Sleep(int nMilliseconds) Sleep(int nMilliseconds)  1 ms granularity on CE 3.0 Sleep(100); // block for 100 ms. Sleep(5); // block for 5 ms. Sleep(0); // yield quantum. Avoid SetTimer() Avoid SetTimer()  Not RT  Message-based, UI-oriented timer

Priority Inversion Mutex ABC Priority Time Blocks on Mutex Acquires Mutex Frees Mutex

Optimizing Tips Avoid priority inversion Avoid priority inversion  Avoid file I/O from RT threads  Avoid graphic calls from RT threads  Avoid UI calls from RT threads Memory Memory  Pre-allocate heap memory  Pre-commit stack memory To Control Paging To Control Paging  Use LoadDriver() - not LoadLibrary()  For individual pages - LockPages()

Measurement Tools ILTIMING – Check Interrupt Latency ILTIMING – Check Interrupt Latency  \wince300\public\common\oak\ utils\iltiming OSBENCH – Thread scheduling OSBENCH – Thread scheduling  \wince300\public\common\oak\ utils\osbench White paper: White paper:  embedded/ce/resources/developing

Measurement APIs QueryPerformanceFrequency() QueryPerformanceFrequency() QueryPerformanceFrequency()  Returns Ticks per Second QueryPerformanceCounter() QueryPerformanceCounter()  Returns Current tick count GetTickCount() GetTickCount()

Discussion

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