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Windows CE Object Store
• Windows CE name for persistent
storage
• Provides storage for the
– Registry
– Databases
– File System
• In a non-volatile portion of RAM
Registry
• To centralize applicationr, user and system
settings
• Consolidates what was done earlier with
autoexec.bat, config.sys, etc.
• Stored as a hierarchy, with each element termed
a key.
• Each key has a default value and several optional
extra values
• Four hierarchies
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HKEY_LOCAL_MACHINE: char. of m/c
HKEY_USERS: default user config.
HKEY_CURRENT_USER: for current user
HKEY_CLASSES_ROOT: types and properties of
supported documents
Registry (contd.)
• RegCeateKeyEx() to create keys
• RegSetValueEx() to update a value of
a key
• RegQueryValueEx() retrieves the
associated type and data
Databases
• CE offers an integrated database not
offered by other Windows versions
• Note that this is not really a DBMS
– No SQL (direct API)
– No concurrency control
– No transactional notion
Terminology
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Volume: A collection of tables
Database: One of these tables
Record: One row of table
Property: A column of the table
Sort Order: A method to quickly
access rows
• Each database can support upto 4
sort orders (specified at creation).
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Databases are stored in a file (called volume).
First mount a volume using CeMountDBVol()
CeCreateDatabaseEx() to create a database
CeOpenDatabaseEx() to open an existing database
– can ask to be notified if someone else modifies
when in use.
• CeWriteRecordProps() to create or update a
record.
• Each call to CeReadRecordProps() returns the next
record in the specified sort order (at open)
• CeSeekDatabase() to seek to a specific record –
record id, matching a value, having the immediate
previous value, etc.
File System
• Portion of object store where files reside
(\Windows)
• Differences from normal Windows:
– No security/access permissions
– No notion of drives (A:, C:, etc.) – everything
is accessible from “\”
– No concept of current directory, always need to
specify from “\”
• When inserting flash cards, they appear
under the directory “\StorageCard1”,
“\StorageCard2”, etc.
File System API
• CreateFile() to create files – analogous to Unix
open
• ReadFile() and WriteFile() to read and write data
from/to files.
• Writes are buffered and flushed to appropriate
device sometime later
• Applications can force the writes with
FlushFileBuffers() call
• File seeking is done with SetFilePointer() call.
• Can use same calls for device interfaces as well.
In addition there is a DeviceIOControl() call similar
to Unix ioctl().
Memory Mapped Files
• Allows normal memory load/store
interface to files
• Also, allows creating shared memory
• Different from traditional Unix in
that it increases the virtual address
space of process. E.g. a process
(normally 32MB) mapping a 4MB file
becomes 36MB, but not all of it is
contiguous
Memory Mapping API
• CreateFileForMapping() is done first
• Then the handle is passed to
CreateFileMapping() which creates a file
mapping object and associates it with the
opened file.
• MapViewOfFile() maps the file in memory
and returns a memory pointer to it.
• When two processes do this, they have
created a shared memory region.
Device Drivers
• Native drivers
– Control low level devices built-in with the
CE platform (audio, battery display,
keyboards …)
– They can have unique APIs
• Stream drivers
– They export the same API
– They usually drive 3rd party devices (GPS
receivers, printers, etc.)
Interface between Kernel and
Native Driver
Kernel
Interrupt
Service
Handler (ISH)
Event
Handler
(EH)
6
4
OAL
1
2
3
7
Interrupt
Service
Routine (ISR)
Native Driver
Interrupt Service Thread
(IST)
5
Platform Dependent
Driver
HARDWARE
• EH in kernel is first invoked.
• EH disables all interrupts and invokes
appropriate ISR in OAL
• ISR performs some minimal processing and
returns interrupt id to kernel
• ISH re-enables all but this interrupt, uses
the interrupt id to signal an event on which
a IST of a native driver is waiting (Event
Object).
• IST may need to perform some hardware
specific actions to process interrupt
• IST then notifies kernel once it is done
• ISH then re-enables this interrupt by
calling some functions in OAL.
Stream Drivers
• Presents the device as being a special
file
• Standard API regardless of the
device
• Strict naming rules: 3 upper case
letters (identifies function prefix) +
single digit + colon
• They can be loaded/unloaded by the
Device Manager.
Loading Drivers
• At boot time, Device Manager loads all drivers
listed under
HKEY_LOCAL_MACHINE\Drivers\Builtin registry
key.
• When a device is connected, the Device Manager
calls the native socket driver to obtain a Plug and
Play id. This id is compared against registry
entries in
HKEY_LOCAL_MACHINE\Drivers\PCMCIA. If
found, that driver is loaded. Else, it calls
functions listed in ….\PCMCIA\Detect that are
Stream Driver functions. If one of them says it
can handle, then that driver is loaded.
• If an application attempts to open a device without
driver loaded, then the application can explicitly
load the driver.
Stream Interface Functions
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XXX_Close()
XXX_Deinit()
XXX_Init()
XXX_IoControl()
XXX_Open()
XXX_PowerDown()
XXX_PowerUp()
XXX_Read()
XXX_Seek()
XXX_Write()