Symbian Programming Overview

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Symbian Programming Overview
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How to program Cellphone?

• Limited to Series 60 phones
• Java MidP 2.0 (see wiki, forums)
• compile offline and load
• limited API
• C
• full API
• non-standard C
• Python -- coming soon

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Getting App onto Phone

• Compile application into .app
• Create package file (.pkg)
• resources files, libraries
• including a digitally signed certificate --
  authentication -- and authors key (.cer and
  .key)
• Installation file (.sis) via makesis tool
• Transfer to phone via email or bluetooth and
  then user installs

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Overview of Symbian

• Symbian is a company that produces an operating
  system
• Originally developed for handheld Psion and
  called Epoc Operating System
• Symbian is 40 owned by Nokia, partly owned by
  Sony Ericson, partly owned by Psion, and others
• Require 70 agreement to make basic changes

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A little history

• Started in early days of C
• Goal to be
• real-time
• small footprint
• small touch-screen
• integrated
• secure reliable

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Biggest Security Flaws

• Applications must be certified
• If not certified, user choice to continue
• Applications either GUI or Server
• a server app can easily hide
• File system not fully exposed to user
• File system has no access control lists
• despite kernel/user execution,
• any application can do anything
• Application can control all keys

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Biggest Programming Issue

• System may run for years
• Persistent state across power downs
• addressbook application may never terminate
• Small memory leaks accumulate over time
• Must write perfect leak-free code!
• unachievable goal
• try anyway

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Why will there be Memory Leaks

• No garbage collection
• No memory protection
• no page tables
• No try, throw, catch
• operating systems calls
• trap harness and leave
• Silly naming conventions

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Keep track of all allocated objects

• Always keep live pointer to anything allocated in
  heap
• can use pointer to deallocate
• extra care when constructing compound classes
• Deallocate after use

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Stacks

• Objects allocated at top of stack
• Top of stack disappears when procedure returns
• Cannot construct objects on stack since they
  maybe constructed in procedure
• Objects go in heap
• No reference counts on objects

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Heap allocation

• Within one procedure
• Allocate pointer to heap object
• Allocate (construct) object on heap
• Use object
• Deallocate object on heap
• Deallocate pointer to heap object

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Pointer to object not on stack

• If pointer is on stack, what happens when there
  is an exception?
• may pop out several levels of stack
• Need to put objects on different type of stack
• one that does not disappear during exception
• keep pointers in heap on cleanup stack

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Cleanup Stack

• Cleanup Stack resides in heap
• what if Construct causes exception?
• Class self new(ELeave) Class(aInt)
• CleanupStackPushL(self)
• self-gtConstruct(aObj)
• CleanupStackPop(self)

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Exception Handling

• On exception, cleanup stack is popped and objects
  are removed.
• (always check for null pointers)
• Exceptions may be handled far back in time of
  program execution

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In the days before try

• TRAPD(error, callExampleL() )
• void CreateObject()
• Object obj new (ELeave) Object
• Trapd is a trap harness
• It calls proceedure callExample()
• Normal return, TRAPD continues
• Exception, has error set to code

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Throwing exceptions

• UserLeave()
• of allocation runs out of memory in a
• new(ELeave)

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Descriptors

• TBuf
• TBufC
• HBufC
• TPtr
• TPtrC

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Active Scheduler

• Non-preemptive scheduler
• Create a scheduler
• Post wait for event(s)
• Return to scheduler
• Handle event

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O2S How it helps you

• Overcome firewalls
• Overcome IP address, Dynamic DNS
• do not have to program in the names of all
  services devices
• Publish and subscribe facility
• HUB is useful resource
• Python based
• UI independence

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O2S Planner

• Better support for publish-subscribe
• Easier to piece together application
• Better Human support

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More on O2S

• Branch in O2S CVS directory
• easier to ask for help
• Name stuff based on group name
• can easily find each other

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Eye-toy

• Playstation 2 game
• Camera watches user
• Identify body outline, especially hands and head
• Hands punch virtual characters
• Head hits balloon or soccer ball

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Mosquito