Symbian OS Presented by: Daniel O'Grady Michael O'Sullivan
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Symbian OS Presented by: Daniel O’Grady Michael O’Sullivan
History / Background
¢ Developed 10 years ago as a proprietary
product.
¢ Forced by the success of Apple’s
iPhone. Nokia took a large share and
pushed for open source.
¢ Nokia/(Symbian) Ltd. & The Symbian
foundation.
¢ Went open source in Feb 2010. Largest
transition in IT history.History / Background
¢ Developers can acquire and modify the
OS free of charge.
¢ Single largest OS in the mobile market
47%, 330 million devices.
¢ Competes with the Linux based Android
from Google.The Product
¢ 3 basic principles.
l the integrity and security of user data
is paramount,
l user time must not be wasted,
l all resources are scarce.
¢ Part of the Mobile Operating System
family.
¢ Written in C++.
¢ Only runs on ARM processorsThe Product
¢ Features
l Request-and-callback implementation.
l Pre-emptive multitasking.
l Memory protection.
l Micro kernel architecture.
l User Interface seperate from the
engine.The Product
l Currently on release 9.4.
l Has 20 million lines of code.
¢ For use on low power battery mobile
devices, e.g. phones & tablets.
¢ Usually flash for secondary storage,
larger devices have disks.
¢ Encroaching into lower end of laptop
market.Design
¢ OO design, employing the Model-
view-controller pattern.
¢ Layers from top to bottom:
l UI Framework.
l Application Services.
l OS Services.
l Base Services.
l Kernel Services & Hardware Interface.Kernel ¢ Micro Kernel, keep what is in the kernel to a minimum. ¢ Contains a scheduler, memory management and device drivers. ¢ Other Services e.g.: Networking, Telephony and Filesystem support are in the OS or Base Services layer.
Kernel
¢ Big on conserving resources eg:
Symbian-specific programming idioms
l descriptors and a cleanup stack.
¢ Introducing EKA2 (rel 8 & 9), a real
time (nano) kernel.
l Provides real time guarantees, APIs
are time bound.Kernel
¢ It uses FAT as the internal file
system, an object-oriented
persistence model was placed over
the underlying FAT to provide a
POSIX-style interface.Symbian Operating System ¢ EKA2 (EPOC Kernel Architecture 2) - The Symbian OS Kernel - Nanokernel ¢ Central Processing Unit ¢ Memory Management
Symbian OS Overview
EKA2 – Symbian OS Kernel
¢ The kernel is responsible for the CPU and
the memory.
¢ Has pre-emptive multithreading.
¢ EKA2 is real-time. Its services are mostly
bounded.
¢ Contains a "nanokernel" which provides the
most basic OS facilities upon which other
layers can be built.
¢ The EKA2 kernel is responsible for memory
management, task management and task
scheduling.EKA2 – Symbian OS Kernel
¢ Symbian OS and EKA2 are modular.
Functionality provided in separate blocks.
¢ EKA2 is single user. There is no concept of
multiple logins to a Symbian OS phone.
¢ EKA2 is a priority based multi-tasking OS,
allocating CPU time based on a threads
priority.
¢ Switches CPU time between multiple
threads, giving the user of the mobile phone
the impression that multiple applications are
running at the same time.EKA2 – Symbian OS Kernel
¢ Builds on the services provided by the
nanokernel.
¢ Provides user-mode threads, processes,
reference-counted objects and handles,
dynamically loaded libraries, inter-thread
communication.
¢ Allows dynamic memory allocation.
¢ Provides the kernel heap, which uses low-
level memory services provided by an entity
known as the memory model.EKA2 – Symbian OS Kernel
¢ EKA2 has five threads, and they are:
¢ The null/idle thread. Idles the CPU, de-
fragments RAM.
¢ The supervisor thread. Cleans up killed
threads and processes.
¢ DFC thread 0. Runs DFCs for general
device drivers, e.g. keyboard.
¢ DFC thread 1. Runs the nanokernel's timer
queue.
¢ Timer thread. Runs Symbian OS relative
and absolute timers.Nanokernel
Nanokernel
¢ Symbian use the term nanokernel, but it is
really a microkernel.
¢ Why use a nanokernel? Very low and
predictable interrupt and thread latencies.
¢ Provides simple, supervisor-mode threads,
along with their scheduling and
synchronization operations.
¢ Services are more primitive than most
embedded RTOSes, but enough to provide
a GSM signalling stack.Nanokernel
¢ Preemptible with interrupts enabled
¢ Initial handler for all interrupts.
¢ Need to prevent other threads from running
in critical sections of code, such as thread
state changes and access to the ready list.
¢ Critical sections are as short as possible
and have bounded execution times.
¢ Critical sections are protected by disabling
pre-emption, possible because these
sections are very short.Nanokernel ¢ Responsible for scheduling ¢ Threads that are ready for execution are kept on a priority-ordered list. ¢ Each nanothread has an integer priority between 0 and 63 inclusive. ¢ Threads with the same priority may be executed using round-robin or FIFO scheduling algorithms.
Nanokernel ¢ What are the limitations on the nanokernel? ¢ Does not do any dynamic memory allocation, i.e. it can't allocate or free memory. ¢ In all of the nanokernel's operations, it assumes that memory has been pre- allocated by other parts of the operating system.
Central Processing Unit
Central Processing Unit ¢ Symbian OS requires a 32-bit microprocessor. ¢ It must be little endian, with a full MMU, user and supervisor/kernel modes, interrupts and exceptions. ¢ All Symbian OS phones have an ARM-based CPU, as do ~75% of the world's mobile phones.
Memory Management
¢ The kernel is responsible for:
¢ Management of the physical memory
resources: RAM, MMU and caches
¢ Allocation of virtual and physical memory
¢ Per-process address space management
¢ Process isolation and kernel memory
protection
¢ The memory aspects of the software loaderMemory Management Unit
¢ Co-ordinates the use of virtual memory.
¢ Sits between the CPU and the system bus,
translating virtual addresses used by
software into physical addresses
understood by the hardware.
¢ The MMU breaks up the flat contiguous
physical memory into pages.
¢ Mostly pages are 4 KB, although larger 64
KB pages and 1 MB sections exist.RAM
¢ A Symbian OS phone will have between 8
and 64 MB of RAM
¢ Quantity of RAM determines the type and
number of applications you can run
simultaneously.
¢ Access speed of the RAM determines
application performance.
¢ The OS itself has low RAM requirements.
¢ Multimedia uses lots of RAM for images and
video recording.Memory Management ¢ Interrupts by peripherals go to Programmable Interrupt Controller ¢ Direct Memory Access (DMA) is used by Symbian OS, and can reduce the interrupt load by a factor of 100.
Other Stuff ¢ Viruses travel on phones via bluetooth, to date none have exploited flaws in Symbian OS. ¢ Since OS9.0 Symbian will only run software that is digitally signed. ¢ Writing apps for Symbian directly is very complicated due to the Symbian- specific programming idioms.
Other Stuff
l Use Integrated Development
Environment (IDE) such as
Carbide.c++ .
l The Express edition is free.
¢ Not just Nokia also used by e.g.
Siemens and Samsung.You can also read
