Transcript Lecture 1 on Windows CE organization.

Operating systems
Windows CE (WinCE).
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Goals
Support lightweight consumer devices:
PDAs.
Set-top boxes.
Simplify porting existing Windows
applications to the new platforms.
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WinCE architecture
Applications
Embedded shell
Remote connectivity
WinCE shell services
Win32 APIs
Kernel
library
GWES
Device
manager
File
manager
OAL
bootload
drivers
Device
drivers
File
drivers
OEM hardware
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IrDA
TCP/IP
Network
drivers
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 kernelmode code).
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Address space
Bottom half is
user space.
Top half is kernel
space.
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2 GB
Kernel space
2 GB
User space
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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.
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User address space
64 slots of 32 MB
each.
Slot 0 is currently
running process.
Slots 1-33 are the
processes.
Slot 63: resource mappings
Slots 33-62: object store,
memory mapped files
…
Slot 3: process
32 processes max.
Object store, memory
mapped files, resource
mappings.
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Slot 2: process
Slot 1: DLLs
Slot 0: current process
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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.
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DLL virtual memory
allocations
User code:
Stack, heap
per thread
Guard section (64K)
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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.
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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.
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Driver architecture
I/O
RM
Device
GWES
PCI bus
battery network
audio
Firewire USB host
PCMCIA
host
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display
touch
mouse
Notification
LED
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.
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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.
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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.
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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.
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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.
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WinCE 4.x interrupts
ISR
ISR
ISR
ISR
ISH
device
All higher
enabled
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Set event
Enable ID
All enabled
Except ID
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All enabled
thread I-ISR OAL kernel HW
IST processing
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.
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Thread quantum
Per-thread quantum.
Default set by OEM.
Use API to set quantum.
Quantum of 0 means run-to-completion.
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System tick
1 ms timer tick normally.
Sleep(N) will generally wake up in N to
N+1 ms.
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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.
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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.
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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.
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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.
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Board support package
Customizes OS for a hardware platform.
Drivers, memory configuration, power
management, etc.
Software development environment
provides tools for BSP development.
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BSP development process
Test
HW
Power
management
Clone
Reference BSP
Add device
drivers
Package
BSP
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Develop
Boot loader
Develop
Minimal kernel
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.
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OAL architecture
Kernel (Microsoft)
RTC
Real-time
clock
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Power
Mgt.
OAL
interrupt
functions
Hardware
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debug
USB/
Ethernet/
Serial