1. Lecture 1. Embedded Systems vs General- Purpose Systems Prof. Taeweon Suh Computer Science Education Korea University COM609 Topics in Embedded Systems

2. Korea Univ Embedded Systems Embedded System is a special-purpose computer system designed to perform one or a few dedicated functions -- Wikipedia  In general, it does not provide programmability to users, as opposed to general purpose computer systems like PC  Embedded systems are virtually everywhere in your daily life 2

3. Korea Univ Embedded Systems (Cont) Even though embedded systems cover a wide range of special-purpose systems, there are common characteristics  Low cost Should be cheap to be competitive  Memory is typically very small compared to a general purpose computer system  Lightweight processors are used in embedded systems  Low power Should consume low power especially in case of portable devices Low-power processors are used in embedded systems 3

4. Korea Univ Embedded Systems (Cont)  High performance Should meet the computing requirements of applications  Users want to watch video on portable devices Audio should be in sync with video  Gaming gadgets like playstation should provide high performance  Real-time property Job should be done within a time limit  Aerospace applications, Car control systems, Medical gadgets are critical in terms of time constraint – Otherwise, it could lead to catastrophe such as loss of life Will talk more about this 4

5. Korea Univ Embedded Systems (Cont) It is challenging to satisfy the characteristics  You may not be able to achieve high performance while maintaining low power consumption and making use of cheap components  So, you got to do your best in a given circumstance to be competitive in the market 5

6. Korea Univ HW/SW Stack of Embedded Systems Identical to the general-computer systems 6 OS / Device Drivers Hardware Application Software

7. Korea Univ Components of Embedded Systems Hardware  It is mainly composed of processor (1 or more), memory, I/O devices including network devices, timers, sensors etc. 7

8. Korea Univ Components of Embedded Systems Software  System software Operating systems  Many times, a multitasking (multithreaded) OS is required, as embedded applications become complicated Networking, GUI, Audio, Video Processor is context-switched to process multiple jobs  Operating system footprint should be small enough to fit into memory of an embedded system In the past and even now, real-time operating systems (RTOS) such as VxWorks or uC/OS-II have been used because they are light-weighted in terms of memory requirement Nowadays, little heavy-weighted OSs such as Windows-CE or embedded Linux (uClinux) are used, as embedded processors support computing power and advanced capabilities such as MMU (Memory Management Unit) Device drivers for I/O devices 8

9. Korea Univ Components of Embedded Systems (Cont) Software (cont.)  Application software Run on top of operating system Execute tasks that users wish to perform  Web surfing, Audio, Video playback 9

10. Korea Univ Real-Time System Real-time operating system (RTOS)  Multitasking operating system intended for real-time applications  RTOS facilitates the creation of real-time systems  RTOS does not necessarily have a high throughput  RTOS is valued more for how quickly and/or predictably it can respond to a particular event Hard real-time systems are required to complete a critical task within a guaranteed amount of time Soft real-time systems are less restrictive  Implementing real-time system requires a careful design of scheduler System must have the priority-based scheduling  Real-time processes must have the highest priority  Priority inheritance (next slide) Solve the priority inversion problem Process dispatch latency must be small 10

11. Korea Univ Priority Inversion Problem Pathfinder mission on Mars in 1997  Used VxWorks, an RTOS kernel, from WindRiver  Software problems caused the total system resets of the Pathfinder spacecraft in mission Watchdog timer goes off, informing that something has gone dramatically wrong and initiating the system reset 11

12. Korea Univ Priority Inversion Problem VxWorks provides preemptive priority scheduling of threads  Tasks on the Pathfinder spacecraft were executed as threads with priorities that were assigned in the usual manner reflecting the relative urgency of these tasks. 12 Task 3 (lowest priority) Task 2 (medium priority) Task 1 (highest priority) Time Task 3 gets semaphore Task 1 preempts Task3 Task 1 tries to get the semaphore Task 3 is resumed Task 2 preempts task 3 Task 3 is resumed Task 3 releases the semaphore Task 1 gets the semaphore and execute Priority Inversion

13. Korea Univ Priority Inheritance A chain of processes could all be accessing resources that the high-priority process needs  All these processes inherit the high priority until they are done with the resource  When they are finished, their priority reverts to its original value 13 Task 3 (lowest priority) Task 2 (medium priority) Task 1 (highest priority) Time Task 3 gets semaphore Task 1 preempts Task3 Task 1 tries to get the semaphore (Priority of Task 3 is raised to Task 1’s) Task 3 is resumed with the highest priority Task 1 completes Priority Inversion Task 3 releases the semaphore

14. Korea Univ Operating Systems for Embedded Systems RTOSs  pSOS  VxWorks  VRTX (Versatile Real-Time Executive)  uC/OS-II Palm OS (source: Wikipedia)  Embedded operating system initially developed by U.S. Robotics-owned Palm Computing, Inc. for personal digital assistants (PDAs) in 1996 Symbian OS (source: Wikipedia)  Proprietary operating system designed for mobile devices by Symbian Ltd.  A descendant of Psion's EPOC and runs exclusively on ARM processors Android  Open Handset Alliance Project  Based on Linux 2.6 kernel  http://code.google.com/android/ 14

15. Korea Univ Operating Systems for Embedded Systems Windows CE (WinCE) (source: Wikipedia)  Microsoft's operating system for minimalistic computers and embedded systems  WinCE is a distinctly different operating system and kernel, rather than a trimmed- down version of desktop Windows Embedded Linux (uClinux, ELKS, ThinLinux) (source: Wikipedia)  The use of a Linux operating system in embedded computer systems  According to survey conducted by Venture Development Corporation, Linux was used by 18% of embedded engineers  Embedded versions of Linux are designed for devices with relatively limited resources, such as cell phones and set-top boxes  Due to concerns such as cost and size, embedded devices usually have much less RAM and secondary storage than desktop computers, and are likely to use flash memory instead of a hard drive  Since embedded devices are used for specific purposes rather than general purposes, developers optimize their embedded Linux distributions to target specific hardware configurations and usage situations These optimizations can include reducing the number of device drivers and software applications, and modifying the Linux kernel to be a real-time operating system  Instead of a full suite of desktop software applications, embedded Linux systems often use a small set of free software utilities such as busybox, and replace the glibc C standard library with a more compact alternative such as dietlibc, uClibc, or Newlib. 15

16. Korea Univ Embedded System Design Flow 16 Planning & Architect (modeling & simulation) Hardware Design with CAD tools ASIC/SoC design ASIC/SoC chip System prototype board Hardware debugging & Software development Final product ASIC: Application-Specific Integrated Circuit SoC: System-on-Chip

17. Korea Univ A General-Purpose Computer System (till 2008) 17 CPU North Bridge South Bridge Main Memory (DDR2) FSB (Front-Side Bus) DMI (Direct Media I/F) Hard disk USB PCIe card Peripheral devices Graphics card But, don’t forget the big picture!

18. Korea Univ Present, Near Future and More… 18 Keep in mind that CPU and computer systems are evolving at a fast pace CPU North Bridge South Bridge Main Memory (DDR2) FSB (Front-Side Bus) DMI (Direct Media I/F) Core 2 Duo – based Systems Core i7– based Systems CPU IOH (Input/Output Hub) South Bridge Main Memory (DDR3) DMI (Direct Media I/F) Quickpath (Intel) or Hypertransport (AMD)

19. Korea Univ x86 History (as of 2008) 19

20. Korea Univ x86 History (Cont.) 20 32-bit (i386) 32-bit (i586) 64-bit (x86_64) 32-bit (i686) 8-bit16-bit4-bit Core i7 2009

21. Korea Univ x86? What is x86?  Generic term referring to processors from Intel, AMD and VIA  Derived from the model numbers of the first few generations of processors: 8086, 80286, 80386, 80486  x86  Now it generally refers to processors from Intel, AMD, and VIA x86-16: 16-bit processor x86-32 (aka IA32): 32-bit processor * IA: Intel Architecture x86-64: 64-bit processor Intel takes about 80% of the PC market and AMD takes about 20%  Apple also have been introducing Intel-based Mac from Nov. 2006 21

22. Korea Univ Chipset We call North and South Bridges as Chipset Chipset has many PCIe devices inside North Bridge  Memory controller  PCI express ports to connect Graphics card  http://www.intel.com/Assets/PDF/datasheet/316966.pdf http://www.intel.com/Assets/PDF/datasheet/316966.pdf South Bridge  HDD (Hard-disk) controller  USB controller  Various peripherals connected Keyboard, mouse, timer etc  PCI express ports  http://www.intel.com/Assets/PDF/datasheet/316972.pdf http://www.intel.com/Assets/PDF/datasheet/316972.pdf Note that the landscape is being changed!  For example, memory controller is integrated into CPU 22

23. Korea Univ PCI, PCI Express Devices 23 PCI (Peripheral Component Interconnect)  Computer bus connecting all the peripheral devices to the computer motherboard PCIe (PCI Express)  Replaced PCI in 2004  Point-to-point connection PCI slot PCI express slots PCI express slot x16 http://www.pcisig.com/specifications/pciexpress/

24. Korea Univ An Old GP Computer System Example 24

25. Korea Univ PCI Express Slots in GP Systems 25 PCI express slot

26. Korea Univ GP Computer System in terms of PCIe 26 North Bridge South Bridge

27. Korea Univ Core i7-based Systems Core i7 860 (Lynnfield) – based system 27 Core i7 920 (Bloomfield) – based system

28. Korea Univ Software Stack 28 Computer Hardware (CPU, Chipset, PCIe cards...) BIOS (AMI, Phoenix Technologies …) Operating System (Linux, Vista, Mac OS …) Applications (MS-office, Google Earth…) API (Application Program I/F) BIOS provides common I/Fs

29. Korea Univ How the GP Computer System Works? 29 x86-based system starts to execute from the reset address 0xFFFF_FFF0  The first instruction is “jmp xxx” off from BIOS ROM BIOS (Basic Input/Output System)  Detect and initialize all the devices (including PCI devices via PCI enumeration) on the system  Provide common interfaces to OS  Hand over the control to OS OS  Manage the system resources including main memory Control and coordinate the use of the hardware among various application programs for the various users  Provide APIs for system and application programming

30. Korea Univ So… What? How is it different from embedded systems?  General-purpose computer systems provide programmability to end-users You can do any kinds of programming on your PC  C, C++, C#, Java etc  General-purpose systems should provide backward compatibility A new system should be able to run legacy software, which could be in the form of binaries with no source codes written 30 years ago  So, general purpose computer system becomes messy and complicated, still containing all legacy hardware functionalities 30

31. Korea Univ 31 x86 Operation Modes Real Mode (= real address mode)  Programming environment of the 8086 processor  8086 is a 16-bit processor from Intel Protected Mode  Native state of the 32-bit Intel processor For example, Windows is running in protected mode  32-bit mode IA-32e mode (64-bit mode)  There are 2 sub modes Compatibility mode 64-bit mode

32. Korea Univ Registers in 8086 Registers inside the 8086  16-bit segment registers CS, DS, SS, ES  General-purpose registers all 16-bits AX, BX, CX, DX, SP, BP, SI, DI Registers in x86-32 32

33. Korea Univ 33 Real Mode Addressing In real mode (8086), general purpose registers are all 16-bit wide Real model  Segment registers specify the base address of each segment  Segment registers CS: Code Segment -> used to store instructions DS: Data Segment -> used to store data SS: Stack Segment -> stack ES: Extra Segment -> could be used to store more data  Addressing method Segment << 4 + offset = physical address Example: mov ax, 2000h mov ds, ax  Data segment starts from 20000h (2000h << 4)

34. Korea Univ 34 Data Segment in Real Mode Memory addressing in real mode (8086) Main Memory (1MB) 2000h DS mov ax, 2000h mov ds, ax mov al, [100h] 100h offset 0x0 0xFFFFF 20000h = 2000h << 4 20100h

35. Korea Univ A20M 8088/8086 allowed only 1MB memory access since they have only 20-bit physical address lines  2 20 = 1MB Memory is accessed with segment:offset in 8086/8088 (still the same though)  What if CS=0xFFFF, IP=0x0020? CS << 4 + IP = 0x100010 But, we have only 20 address lines. So, 8088 ends up accessing 0x00010 ignoring the “1” in A21 Some (weird?) programmers took advantage of this mechanism 35

36. Korea Univ A20M (Cont) How about now?  Your Core 2 Duo has 48-bit physical address lines  What happens if there is no protection in the previous case Processor will access 0x100010, breaking the legacy code  So, x86 provides a mechanism called A20M (A20 Mask) to make it compatible with the old generations 36

37. Korea Univ A20M (Cont) 37

38. Korea Univ Another Example Protected mode addressing (32-bit)  As application programs become larger, 1MB main memory is too small  Intel introduced protected mode to address a larger memory (up to 4GB)  But, Intel still wants to use 16-bit segment registers for the backward compatability  How to access a 4GB space with a 16-bit register? 38

39. Korea Univ 39 Protected Mode Addressing Index Segment Selector TITI RPLRPL 15 3 2 1 0 GDTLDT TI = 0 TI = 1 Segment Descriptor Base Access info 31 0 19 0 Limit Hardware Inside the CPU (Registers) Main memory Visible to software Invisible to software

40. Korea Univ 40 Segment Descriptor Format Software (OS) creates descriptor tables (GDT, LDT)

41. Korea Univ 41 Address Translation in Protected Mode

42. Korea Univ One More Example 8259 Interrupt Controller 42 IR0 IR1 IR2 IR3 IR4 IR5 IR6 IR7 INTR IR0 IR1 IR2 IR3 IR4 IR5 IR6 IR7 INTR INTA INTR 82C59A (Master) 82C59A (Slave) CPU (8086) CPU North Bridge South Bridge Main Memory (DDR) FSB (Front-Side Bus) DMI (Direct Media I/F) Still in South Bridge