Chapter 1

Most servers use their own .exe to generate their own process. For instance, ewsrv.exe is
the window server and efile.exe is the file server.
As we saw earlier, some servers piggyback into the process of others to minimize contextswitching
overheads. The main server in such a group uses its own process – for instance,
c32exe.exe launches the serial communications server. Other servers use a DLL and
launch their own thread within the main server thread.
A console application, such as hellotext.exe, is built into its own .exe. A console application
must create its own console, which it can then use to interact with the user.
Most GUI applications are like hellogui.app. They are actually polymorphic DLLs whose main
entry point, NewApplication(), creates and returns a CEikApplication-derived object.
The application process is created by a small .exe, apprun.exe, to which the .app name is
passed as a parameter. If the application wants to edit an embedded document, it can do so
without creating a new process by loading the.app for the embedded document directly in
the same thread.
2.5 Power Management
Power management is probably the single most difference between a desktop system and a
portable system:
� Power has to be used efficiently. Battery life – even with rechargeable batteries –
makes a difference to how the user thinks of the device. So also does battery weight.
Symbian OS needs to work effectively on lower-speed, lower-power hardware, than that
used by desktop PCs.
� Certain parts of the system should still be able to run while the system is apparently
off. For example, when an alarm is due, the machine should be turned on so that the
alarm can sound. For modern smartphones, the phone may need to react to an
incoming call or SMS. This means that the system should switch from a low power
mode to being in an active state.
� Even if all power is removed suddenly, the system should do what it can to save critical
information, so that there is a possibility of a warm boot when power returns (rather than
a cold boot).
As an application or server programmer, your task is easier than that of the kernel. But, you
still get involved in power management. You have to write your programs efficiently to make
the best use of a Symbian OS phone's scarce resources – this applies as much to power as
to available RAM, CPU speed, and so on.
The deeper you delve into the system, the more complicated power management becomes.
For instance, as a device driver programmer, you can see that power management is more
complex than simply machine on/off. The user thinks the machine is off if the display is
turned off. But each hardware component is responsible for its own power management. A
communications link driver should turn the physical device off if it's not needed. The kernel
scheduler even turns the CPU off if all threads are waiting for an event. Every possible step
is taken to save power and ensure that user data is retained even in the most difficult powerloss
situations.
2.6 The Kernel and E32
The most fundamental component of Symbian OS is E32. E32 consists of the kernel and
user library. The kernel is entirely privileged. The user library, euser.dll, is the lowestlevel
user-mode code. It offers library functions to other user-mode code and controlled
access to the kernel.