© 2003 Wayne Wolf Overheads for Computers as Components Operating systems zWindows CE (WinCE).

© 2003 Wayne WolfOverheads for Computers as

Components

Operating systems

Windows CE (WinCE).


Components

Goals

Support lightweight consumer devices: PDAs. Set-top boxes.

Simplify porting existing Windows applications to the new platforms.


Components

WinCE architecture

OEM hardware

OALbootload

driversDevicedrivers

Filedrivers

Networkdrivers

Kernellibrary

GWESDevice

managerFile

managerIrDA TCP/IP

Win32 APIs

WinCE shell services

Embedded shellRemote connectivity

Applications


Components

Virtual memory

WinCE uses virtual memory. Most devices don’t have disk drive.

Code can be paged from ROM, etc.WinCE suports a flat 32-bit virtual address

space.Virtual address may be:

Statically mapped (kernel-mode code). Dynamically mapped (user-mode and some

kernel-mode code).


Components

Address space

Bottom half is user space.

Top half is kernel space.

User space2 GB

Kernel space2 GB


Components

Kernel address space

Operating system (nk.exe).Statically mapped virtual addresses.

Up to 512 MB of physical resources can be statically mapped.

Control of static mapping varies: OEM control for ARM and x86. CPU control for SHx and MIPS.


Components

User address space

64 slots of 32 MB each.

Slot 0 is currently running process.

Slots 1-33 are the processes. 32 processes max.

Object store, memory mapped files, resource mappings.

Slot 0: current process

Slot 1: DLLs

Slot 2: process

Slot 3: process

…

Slots 33-62: object store,memory mapped files

Slot 63: resource mappings


Components

Process slot

Includes code, DLL and virtual allocations.

Virtual allocations are 64 KB-aligned; 4KB pages can be committed within an allocation.

Movement: DLL allocations start at

the top and grow down. Process and general

allocations start at the bottom and grow up.

Guard section (64K)

User code: Stack, heapper thread

DLL virtual memoryallocations


Components

API calls

System call may be to DLL, another EXE.

COREDLL provides link between system API and EXE.

System call: Exception caught by kernel. Kernel determines which EXE gets the

call.


Components

Driver structure

A driver is a DLL with particular interface points.

Hosted by a device manager process space (may be GWES).

Handle interrupts by dedicated IST thread.

Synchronize driver and application via critical sections and MUTEXes.


Components

Driver architecture

DeviceI/ORM

GWES

PCI bus display

touch

mouseNotification

LED

battery network audio Firewire USB host

PCMCIAhost


Components

Device manager

Always-running user-level process.Contains the I/O Resource Manager.Loads the registry enumerator DLL

which in turn loads drivers.Provides power notification

callbacks.


Components

Registry enumerator

DLL (RegEum.dll). Re-entrant, supports hierarchical usage.

Driver loading: RegEnum scans registry, loads bus drivers. Bus driver scans bus, locates devices. Searches registry for device information. Loads appropriate drivers. Sends notification that interface is

available.


Components

Interrupt handling

Work divided into two sections: Interrupt service routine (ISR):

Kernel mode service.May be static or installable.

Interrupt service thread (IST):User mode thread.


Components

Static ISR

Built into the kernel. SHx and MIPS must be written in assembler,

limited register availability.

One-way communication from ISR to IST. Can share a buffer but location must be

predefined.

Nested ISR support based on CPU, OEM’s initialization.

Stack is provided by the kernel.


Components

Installable ISR

Can be dynamically loaded into kernel.

Loads a C DLL.Can use shared memory for

communication.ISRs are processed in the order they

were installed.Limited stack size.


Components

WinCE 4.x interrupts

All higherenabled

HW

kernelO

AL

I-ISR

thread

All enabledExcept ID

All enabled

ISH Set event Enable ID

ISR ISR

ISR ISR

IST processing

device


Components

Kernel scheduler

Two styles of preemptive multitasking. Thread runs until end of quantum. Thread runs until higher priority thread is ready

to run.Round-robin within priority level.Quantum is defined by OEM and application.Priority inheritance to control priority

inversion.256 total priorities.

Top 248 can be protected by the OEM.


Components

Thread quantum

Per-thread quantum. Default set by OEM.

Use API to set quantum.Quantum of 0 means run-to-

completion.


Components

System tick

1 ms timer tick normally.Sleep(N) will generally wake up in N

to N+1 ms.


Components

Causes of interrupt latency

ISR: Amount of time that interrupts are turned off. Time required to vector ISR, save registers,

etc.

IST: Time spent in ISR. Time spent in Kcall. Thread scheduling time.


Components

Improvements to latency in WinCE 4.x

Less non-preemptable code. Some routines split into several smaller

routines.Kernel data structures moved to

statically mapped virtual addresses.Special-case ISTs provided.Improved priority inversion handling.


Components

Controlling scheduling/latency

Thread scheduling: Set priorities appropriately, choose proper quantum.

Memory: Preallocate memory, threads, sync objects.

Understand device characteristics: I/O-based access may incur a penalty.

On x86 avoid using CMOS real-time clock, use software real-time clock.

Disable idle processing.Disable demand paging.


Components

Real-time measurement

ILTiming Software-based real-time measurement

tool.Measures ISR latency from IRQ to ISR.Measures IST latency from end of ISR to

start of IST.

Kernel tracker Tracks interrupts, TLB misses, and

priority inversion.


Components

Board support package

Customizes OS for a hardware platform. Drivers, memory configuration, power

management, etc.Software development environment

provides tools for BSP development.


Components

BSP development process

TestHW

CloneReference BSP

DevelopBoot loader

DevelopMinimal kernel

Add devicedrivers

Powermanagement

PackageBSP


Components

Boot loader

The Boot loader loads an executable image and runs it. Loadable by Ethernet, USB, serial, local

flash, etc. Memory may be flash or ROM. May need different development,

production loaders.


Components

OAL architecture

Kernel (Microsoft)

HardwareReal-time

clock

USB/Ethernet/

Serial

OALRTCPowerMgt.

interruptfunctions

debug

© 2003 Wayne Wolf Overheads for Computers as Components Operating systems zWindows CE (WinCE).

Documents

wayne wolf overheads

gb slide

gb kernel space

user space

components static isr

device manager process

kernel mode code

virtual address space