Windows CE Object Store

1
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

2
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
• 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

3
Registry (contd.)

• RegCeateKeyEx() to create keys
• RegSetValueEx() to update a value of a key
• RegQueryValueEx() retrieves the associated type
  and data

4
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

5
Terminology

• 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).

6

• 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.

7
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.

8
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().

9
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

10
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.

11
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.)

12
Interface between Kernel and Native Driver
Kernel
Interrupt Service Handler (ISH)
Event Handler (EH)
6
Native Driver
4
Interrupt Service Thread (IST)
OAL
2
3
1
7
5
Interrupt Service Routine (ISR)
Platform Dependent Driver
HARDWARE
13

• 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.

14
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.

15
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.

16
Stream Interface Functions

• XXX_Close()
• XXX_Deinit()
• XXX_Init()
• XXX_IoControl()
• XXX_Open()
• XXX_PowerDown()
• XXX_PowerUp()
• XXX_Read()
• XXX_Seek()
• XXX_Write()