An Overview of Palm OS

1
An Overview of Palm OS

• Designed for special hardware
• small screen ( 160 x 160 )
• less processing power than desktop PCs
• quick turnaround expected
• limited memory ( 512k 8MB )
• no disk drive or PCMCIA disk

2
The Appearance of a PalmPilot
3
System Architecture
4
Memory Orgnization

• Motorola 68328 uses 32-bit addresses
• External data bus is only 16 bits wide
• ROM - stores the main suite of applications ( the
  OS itself)
• RAM - stores additional and replacement
  applications system extensions
• RAM - dynamic RAM storage RAM

5
Dynamic RAM

• Served as temporary space for allocation
• Analogous to the RAM installed in a typical
  desktop system
• Is cleaned after reboot
• Implement a single heap that provides memory for
  dynamic allocations( TCP/IP, IrDA, )

6
Storage RAM

• Holds nonvolatile user data ( appointments, to do
  lists, memos, address lists, )
• Is accessed via calling the database manager or
  the resource manager
• Analogous to the disk drive of a typical desktop
  system

7
Memory Chunks and Heaps

• A chunk - contiguous memory between 1byte 64 KB
  that has been allocated by the Palm OS memory
  manager
• Each chunk resides in a heap
• Memory manager allocates memory in the dynamic
  heap
• Data manager allocates memory in the storage heap

8
Memory Heaps

• Each heap has a unique heap ID
• The heap with heap ID 0 is the dynamic heap
• Only the dynamic heap is reinitialized through
  soft reset cycles

9
Movable / Nonmovable Chunks

• Each chunk is referenced by a local ID
• The local ID of a nonmovable chunk the offset
  of the chunk from the base address of the card
• The local ID of a movable chunk the offset of
  the master pointer to the chunk from the base
  address of the card

10
The Memory Manager

• The functions of the memory manager
• allocating new chunks
• disposing of chunks
• resizing of chunks
• locking and unlocking chunks
• compacting heaps when they become fragmented

11
Heap Structure
Heap

• Master pointer table stores 32-bit pointer to
  movable chunks
• Movable chunks are allocated at the beginning

Heap Header
Master pointer table
Movable chunks
Non-movable chunks
12
Chunk Structure

• Each chunk begins with an 8-byte header followed
  by that chunks data
• FlagssizeAdj flag
• high nibble set for free chunk
• low nibble reqSize size - 8 - this value
• size field( 3 bytes)
• the size of the chunk, which is larger than the
  size requested by the application , including the
  chunk header itself

13
Chunk Structure(cont.)

• Lockowner byte
• high nibble the lock count, which is
  incremented when being locked
• low nibble the owner ID of the memory chunk
• hOffset field( 3 bytes)
• the distance from the master pointer to the chunk
  header, divided by two

14
The Data Manager

• The database is analogous to disk
• A database is a collection of records
• A record is mapped to a memory chunk
• A database accesses its records by storing their
  local IDs
• An application requests a particular record in a
  database by index

15
The Resource Manager

• Resources store the UI elements of an
  application, such as images, fonts, dialog
  layouts,
• Resource manager Data manager with the
  additional ability of tagging each chunk of data
  with a unique resource type and resource ID

16
Application Structure

• Single threaded
• Event-driven
• PilotMain() corresponds to main() in C
• PilotMain -- Response to launch codes
• An event loop in response of a normal launch

17
Flowchart of event handling
18
Developing Apps on Palm

• Various development tools
• Code Warrior for Palm OS
• Palm SDK (header files, documents, examples)
• GCC
• POSE - An open source Palm emulator runs on
  Windows, Mac and UNIX

19
Conclusion

• The Palm OS provides a good platform for
  developing Palm apps
• The Palm OS provides various libraries for
  communicating with PCs
• A good OS design is not necessarily having the
  most advanced feature, but having the best
  integration of the hardware

20
The End

• B86506053 ???
• B86506025 ???