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COM609 Topics in Embedded Systems. Lecture 1. Embedded Systems vs General-Purpose Systems. Prof. Taeweon Suh Computer Science Education Korea University. Embedded Systems. Embedded systems are virtually everywhere in your life
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COM609 Topics in Embedded Systems Lecture 1. Embedded Systems vs General-Purpose Systems Prof. Taeweon Suh Computer Science Education Korea University
Embedded Systems • Embedded systems are virtually everywhere in your life • Embedded systems cover a wide range of electronics gadgets such as iPhone, Android phone, GPS, Refrigerator, Washer, TV..
Embedded Systems • Embedded System is a special-purpose computer systemdesigned to perform one or a few dedicated functions - Wikipedia • Embedded System market is super competitive
iPhone Generations Original iPhone (iPhone 2G) iPhone 3GS iPhone 4 iPhone 3G June 2010 June 2007 June 2008 June 2009 iPhone 5 iPhone 4S Sep. 2012 Oct. 2011 http://apple.wikia.com/wiki/IPhone_3G http://en.wikipedia.org/wiki/History_of_the_iPhone
Smartphone War http://www.sleetherz.com/2011/10/smartphone-war-in-fatal-three-way-iphone-4s-vs-droid-razr-vs-galaxy-nexus/
Embedded Systems • 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
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
Embedded Systems (Cont) • It is challenging to satisfy the characteristics • You may not be able to achieve high performance while utilizing cheap components and maintaining low power consumption • So, you got to do your best in a given circumstance to be competitive in the market
HW/SW Stack of Embedded Systems • Identical to the general computer systems Application Software OS / Device Drivers Hardware
Components of Embedded Systems • Hardware • It is mainly composed of processor (1 or more), memory, I/O devices including network devices, timers, sensors etc.
iPhone 4 Teardown http://www.ifixit.com/Teardown/iPhone-4-Teardown/3130/1 http://news.cnet.com/8301-13924_3-20006904-64.html GSM (Global System for Mobile communications): 2G, 3G, 4G .. UMTS (Universal Mobile Telecommunications Systems): one of 3G technologies being developed into 4G
iPhone 4 Teardown 512MB Mobile DDR Audio Codec (Cirrus Logic) Samsung flash memory (32GB): K9PFG08 A4 Processor (ARM Cortex A8) designed by Apple manufactured by Samsung GSM and more GSM (Global System for Mobile communications): 3G
iPhone 4 Teardown • Accelerometer detects when the user has rotated the device from portrait to landscape, then automatically changes the contents of the display accordingly • Proximity sensor detects when you lift iPhone to your ear and immediately turns off the display to save power and prevent inadvertent touches until iPhone is moved away • Ambient light sensor automatically adjusts the display’s brightness to the appropriate level for the current ambient light, enhancing the user experience and saving power at the same time
iPhone 5 Teardown Accelerometer Touchscreen controller • A6 application processor, based off the ARMv7 ISA • 1GB Elpida LP (Low Power) DDR2 integrated according to Chipworks LTE modem 16GB NAND Flash from Hynix Wi-Fi module 3-axis gyroscope http://www.ifixit.com/Teardown/iPhone+5+Teardown/10525/2
Galaxy S3 Teardown Samsung 16GB eMMC (MultiMediCard) + 64MB NAND Flash Intel Wireless Processor Exynos 4412: Quad-core A9 with 1GB DDR2 http://www.samsung.com/ http://www.ifixit.com/Teardown/Samsung-Galaxy-S-III-Teardown/
Exynos 4412 Block Diagram PoP: Package-on-Package
Galaxy Note Teardown Flip-chip DRAM on App. Processor • K3PE7E700B-XXC1 low power 1GB DDR2 • S5PC210 Exynos 4210 : ARM Cortex A9 (Dual-core) 1.4GHz with Mali-400 MP GPU
Galaxy Note Teardown Yamaha Audio Codec Audio Processor LCD Driver STMicroelectronics’ Gyroscope
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 • CPU 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 and uC/OS-II have been used because they are light-weighted in terms of memory requirement • Nowadays, heavy-weighted OSs such as iOS, Android, Windows Mobile, and 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
Components of Embedded Systems (Cont) • Software (cont.) - Applicationsoftware • Run on top of operating system • Execute tasks that users wish to perform • Web surfing, Social Network Service, Audio, Video playback
Real-Time Systems • Real-time operating system (RTOS): Multitasking operating system for real-time applications • RTOS is valued for how quickly and/or predictably 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 Hard real-time systems
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
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. Task 1 tries to get the semaphore Task 1 gets the semaphore and execute Task 1 preempts Task3 Priority Inversion Task 1 (highest priority) Task 2 (medium priority) Task 2 preempts task 3 Task 3 (lowest priority) Task 3 is resumed Time Task 3 gets semaphore Task 3 is resumed Task 3 releases the semaphore
Priority Inheritance • A lower priority process could be accessing a critical section (a shared resource) that the higher priority process needs • The process with a lower priority inherits the higher priority until they are done with the resource • When they are finished, its priority reverts to its original value Task 1 tries to get the semaphore (Priority of Task 3 is raised to Task 1’s) Task 1 preempts Task3 Task 1 completes Priority Inversion Task 1 (highest priority) Task 2 (medium priority) Task 3 (lowest priority) Time Task 3 gets semaphore Task 3 is resumed with the highest priority Task 3 releases the semaphore
Operating Systems for Embedded Systems • RTOSs • pSOS • VxWorks • VRTX (Versatile Real-Time Executive) • uC/OS-II • Palm OS & Symbian OS(source: Wikipedia) • Palm OS: Embedded operating system initially developed by U.S. Robotics-owned Palm Computing, Inc. for personal digital assistants (PDAs) in 1996 • Symbian OS: Proprietary operating system designed for mobile devices by Symbian Ltd. A descendant of Psion's EPOC and runs exclusively on ARM processors • Android (http://www.android.com/) • Open Handset Alliance Project • Based on modified version of Linux 2.6 kernel • Currently supporting ARM, MIPS, and x86
Operating Systems for Embedded Systems • uClinux (source: Wikipedia) - as of 2009 • 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.
Embedded System Design Flow ASIC/SoC design ASIC/SoC chip Hardware Design with CAD tools Planning & Architect (modeling & simulation) System prototype board Hardware debugging & Software development Final product • ASIC: Application-Specific Integrated Circuit • SoC: System-on-Chip
A General-Purpose Computer System (till 2008) CPU Main Memory (DDR2) FSB (Front-Side Bus) North Bridge Graphics card DMI (Direct Media I/F) Peripheral devices South Bridge Hard disk USB PCIe card But, don’t forget the big picture!
Past, Present and More… • Core i7 (Ivy Bridge) – based Systems • Core 2 Duo – based Systems Main Memory (DDR2) CPU FSB (Front-Side Bus) North Bridge South Bridge DMI (Direct Media I/F) Keep in mind that CPU and computer systems are evolving at a fast pace! • FDI: Flexible Display Interface • SPI: Serial Peripheral Interface • SMBus: System Management Bus
x86 History (Cont.) 4-bit 8-bit 16-bit 32-bit (i386) 64-bit (x86_64) 32-bit (i586) 32-bit (i686) 2009 2011 2nd Gen. Core i7 (Sandy Bridge 1st Gen. Core i7 (Nehalem) 2012 3rd Gen. Core i7 (Ivy Bridge)
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 * aka: also known as
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 • 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 • Note that the landscape is being changed! • For example, memory controller is integrated into CPU
PCI, PCI Express Devices • 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 express slot x16 PCI express slots PCI slot http://www.pcisig.com/specifications/pciexpress/
PCI Express Slots in GP Systems PCI express slot
GP Computer System in terms of PCIe North Bridge South Bridge
Software Stack Applications (MS-office, Google Earth…) API (Application Program I/F) Operating System (Linux, Vista, Mac OS …) BIOS provides common I/Fs BIOS (AMI, Phoenix Technologies …) Computer Hardware (CPU, Chipset, PCIe cards ...)
How the GP Computer System Works? • 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
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 providebackward 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
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 if 32-bit Windows is installed on your PC • 32-bit mode • IA-32e mode (IA-32 Extended Mode) • There are 2 sub modes • Compatibility mode • 64-bit mode
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
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)
Data Segment in Real Mode • Memory addressing in real mode (8086) 0xFFFFF Main Memory (1MB) mov ax, 2000h mov ds, ax mov al, [100h] 20100h offset 100h DS 2000h 20000h = 2000h << 4 0x0
A20M • 8088/8086 allows only 1MB memory access since they have only 20-bit physical address lines • 220 = 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
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
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?
15 3 2 1 0 Index TI RPL Segment Selector TI = 1 TI = 0 Visible to software Invisible to software 31 0 19 0 Base Limit Access info Protected Mode Addressing Hardware Inside the CPU (Registers) Main memory GDT LDT Segment Descriptor Segment Descriptor Segment Descriptor Segment Descriptor Segment Descriptor Segment Descriptor Segment Descriptor Segment Descriptor Segment Descriptor Segment Descriptor • TI: Table Indicator • RPL: Requested Privilege Level
Segment Descriptor Format • Software (OS) creates descriptor tables (GDT, LDT)