Lecture 1 on Windows CE organization.
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Description
Operating systems Windows CE (WinCE).
© 2003 Wayne Wolf
Overheads for Computers as Components
Goals Support lightweight consumer devices: PDAs. Set-top boxes.
Simplify porting existing Windows applications to the new platforms.
© 2003 Wayne Wolf
Overheads for Computers as Components
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 © 2003 Wayne Wolf
Overheads for Computers as Components
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). © 2003 Wayne Wolf
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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.
© 2003 Wayne Wolf
Overheads for Computers as Components
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. © 2003 Wayne Wolf
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. © 2003 Wayne Wolf
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.
© 2003 Wayne Wolf
Overheads for Computers as 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. © 2003 Wayne Wolf
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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.
© 2003 Wayne Wolf
Overheads for Computers as 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. © 2003 Wayne Wolf
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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.
© 2003 Wayne Wolf
Overheads for Computers as 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.
© 2003 Wayne Wolf
Overheads for Computers as 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. © 2003 Wayne Wolf
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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 Overheads for Computers as Components
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. © 2003 Wayne Wolf
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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.
© 2003 Wayne Wolf
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System tick 1 ms timer tick normally. Sleep(N) will generally wake up in N to N+1 ms.
© 2003 Wayne Wolf
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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.
© 2003 Wayne Wolf
Overheads for Computers as 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. © 2003 Wayne Wolf
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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. © 2003 Wayne Wolf
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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. © 2003 Wayne Wolf
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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.
© 2003 Wayne Wolf
Overheads for Computers as Components
OAL architecture Kernel (Microsoft)
RTC
Real-time clock © 2003 Wayne Wolf
Power Mgt.
OAL
interrupt functions
Hardware Overheads for Computers as Components
debug
USB/ Ethernet/ Serial
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