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Difference between booting a PC or an Embedded System BUILDING AND PORTING EMBEDDED OPERATING SYSTEMS.

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Presentation on theme: "Difference between booting a PC or an Embedded System BUILDING AND PORTING EMBEDDED OPERATING SYSTEMS."— Presentation transcript:

1 Difference between booting a PC or an Embedded System BUILDING AND PORTING EMBEDDED OPERATING SYSTEMS

2 THE BOOTING PROCESS Power On BIOS GRUB Kernel Get Bootloader Get Kernel Power On X-Loader U-Boot Kernel Get Bootloader Get Kernel PC Embedded

3 PCs are a highly modular platform. Most components are in sockets or slots that permits easy replacement. Embedded Systems tend to solder their components directly to the PCB as they dont need to be replaced. EMBEDDED SYSTEM VS PC

4 i7-930 i7-940 i7-960 i7-950 i7-970 i7-920 i7-980X i7-965X



7 USB Audio Codec USB 3.0 Gigabit Ethernet S-ATA 3 & 6Gbps IDE & Floppy Intel PCH

8 EMBEDDED SYSTEM VS PC TI OMAP 3730 Processor 512MB PowerVR SGX530 Graphics All soldered directly to the board. Not intended for replacements.

9 PC booting is a much longer process than for embedded systems. Desktop PCs are by far the worst due to their massive compatibility issue Laptops are faster because their components are much more controlled. EMBEDDED SYSTEM VS PC Desktop PC: Gigabyte GA-X58A-UD3R, Intel Core 4.2GHz, 12GB DDR3-1600, GeForce GTX580, Crucial M4 256GB SSD Laptop PC: Dell XPS 15 L502x, Intel Core 2.2GHz, 6GB DDR3-1600, Intel HD3000 & GeForce GT540M, Western Digital Caviar Black 750GB.


11 BIOS stands for Basic Input Output System First performs Power on self test and initializes Memory, PCI bus, Video, storage, Network(PXE), HID and any other systems a bootloader may need to load the OS. Allows user to choose hardware settings within a simple UI X86 always starts CPU in real mode. 20 bit segmented memory address space Only 1 MiB of addressable memory. BIOS


13 Post POST search for a bootable drive and copy 512byte MBR to RAM. This 512bytes is the MBR Partition table 64b Two byte boot signature Optional Disk timestamps and signatures First stage Bootstrap code takes up the rest The BIOS yields control to the bootstrap who's only task is to locate and execute a more complex second stage bootloader (grub,BOOTMGR,NTLDR) BIOS

14 What is a bootloader? Program used to load an operating system or another boot loader. Boot loaders run in Real mode and use BIOS provided code Operating systems replace BIOS code with their own. What is a second stage bootloader? Programs like GRUB, LILO or NTLDR allow multi-boot systems They are aware of file systems Allow creation of ram discs in memory to boot the linux kernel Once the kernel has retrieved all the information it requires in Real mode it will change the cpu to protected mode providing support for virtual memory, memory protection, multitasking and code privilege levels. Bootloader

15 What is it? Unified Extensible Firmware Interface Replacement for BIOS Improvements Not a single piece of firmware but a programmable software interface. It is hardware independent It provides a standard method of interfacing with firmware during the boot process It's faster due to using Block I/O over interrupts UEFI – The Future?

16 64bit version can address all system memory while booting. Can boot from disks larger than 2TB Pre-boot networking support Mouse usable in boot options You can mount partitions and read file systems Doesn't solve the problem of requiring two drivers. One for the firmware and one for the operating system. Secure Boot(arguably) UEFI – The Future?


18 IGEP boot process ROM Code U-Boot X-Loader Kernel

19 ROM Code What does the IGEP ROM code do? Code is executed in a known location in ROM Minimal Configuration is performed Some clocks set Some memories and peripherals initialised Searches boot devices for suitable boot image Supports serial, SD card, NAND flash and USB amongst others. Boot order is defined by a set of GPIO configuration pins referred to as SYSBOOT On finding the first x-loader image it is copied to SRAM and then executed

20 Serial Boot ID is written out to the serial port and a response is waited for. If response received within time limit ROM will transfer data received from serial port to SRAM and execute it. SD Boot The ROM code looks for a suitably formatted SD card on the MMC controllers. If a readable partition is found directory is scanned for a specially signed file called an "MLO". Assuming the file is as expected, it is transferred into the internal SRAM and control is passed to it. NAND\eMMC If NAND is in the boot list the ROM code will attempt to load the first sector, skipping it if its bad, corrupt or blank. If it reaches the 4th sector and no good sector has been found it will move on. If a good sector is found then it will load the contents to ram and then start executing it. ROM Code

21 X-loader What is x-loader? X-loader is a first stage boot-loader that implements a subset of the features of u-boot. It's small enough to fit in on-chip memory but still provides the ability to configure the pin muxing, clocks, serial console and DDR access to load the fully featured u-boot into the second stage boot loader. In IGEP a copy of the x-loader is part of the NAND Not limited to 512bytes MLO files Through MLO files the need for a second stage boot loader can be removed. An MLO file is a an x-loader file that has been given a header with the size of the image and deployment memory location. You can optionally define clock frequency amongst other things MLO files allow zImages to be booted without the need for a second stage boot loader Serial and SD X-loader supports transfering an image to the board using kermit over a serial connection and will also load a uboot.bin file stored on the SD.

22 Watch out! Boot-loaders are doing configuration that the kernel is not!

23 JTAG Initially devised for testing printed circuit boards with its boundary scanning functionality JTAG is now used extensively for debugging, programming CPLDS and initialising flash memory. Can be useful to recover bricked devices or write new firmware to NAND on restricted devices. But the IGEP is un-brickable Tools like OpenOCD and GDB ARM have successfully been used on OMAP530 devices like the beagleboard.



26 QNX is a Canadian microkernel-based RTOS. Device drivers are all run as userspace applications outside the kernel. Used in many applications, mainly automotive systems. HAM (High Availability Manager). Adaptive Partitioning Scheduler. Safety critical certification. QNX owned by RIM. Tightly coupled bootloader and kernel. Transparent distributed networking. QNX?

27 Most general purpose operating systems (such as linux) avoid becoming too tightly coupled with their bootloaders. This has led to bootloaders which support a multitude of functions. An RTOS developer can take advantage of this by using the generic bootloader (and its more advanced capabilities (NFS, ping) to ensure hardware works, and easily bring it to life. During development this general purpose bootloader can be effectively used as a bootloader loader. The high-functionality (and easy to hack!) bootloader (i.e. U-Boot) can then be removed from a shipped product, leaving behind only a basic tightly-coupled version. BOOTLOADER/OS INTERACTION

28 QNX BOOTING U-Boot Startup QNX Kernel On-Chip boot ROM code generally causes the CPU to perform minimal initialisation of peripheral such as NAND Flash and instructs it to begin reading code from there into memory and executing it. This code can be a standard embedded bootloader such as U-Boot, or it can be a QNX IPL. U-Boot loads the QNX IPL image into memory, and begins executing it. The IPL is an Initial Program Loader which is responsible for initialising basic hardware and passing control to Startup code, and subsequently the QNX Kernel. IPL

29 Begins in assembly, performs initialisation for HLL. Initialises CPU/(some) Peripheral Clocks. Initialises basic I/O (serial). Minimal pin multiplexing for required peripherals (i.e. SDHC hardware). Reads in and decompresses IFS image (ramdisk + kernel). Includes basic (FAT) filesystem drivers for SDHC reading. Passes control to Startup Can start minidrivers for device interaction before OS/Kernel even begins booting. QNX IPL CODE

30 Startup begins in C language, initialises most peripherals, and sets up important kernel structures. The QNX kernel expects a syspage structure to exist at a pre- defined location in memory. This structures provides important information about the host system. Enables CPU SMP operation (multiple-cores). Often re-does initialisation done by IPL (such as serial I/O) to enable more advanced functionality. Informs minidrivers of new environment before passing control to kernel. QNX STARTUP CODE

31 Indicates CPU type (e.g. ARM) and vital information (e.g. number of cores), and other supported features such as NEON extensions. Provides access to hardware-specific function callouts made available to the system before the Kernel was running. Provides information about the memory environment in which the kernel is running. Information about bus devices, IRQs. Information about connected peripherals and device trees for /dev population. SYSPAGE

32 Prevents need for auxillary processors for instant-on peripheral ineraction. Linked against bootloader code. Called periodically during startup, initially with polling and then interrupts when they become available. Full drivers are allowed access to minidriver memory once the kernel has loaded so they can take over without data loss. Make use of I/O hardware within 10ms of power-on. MINIDRIVERS

33 QNX Implements its own FS-aware bootloader (IPL). This bootloader is tightly coupled with its own system initialisation and kernel. This bootloader is only configurable via source code, unlike U- Boot or Grub. Source code for bootloader and startup is freely available for a variety of hardware (kernel is not): /wiki/BSPAndDrivers /wiki/BSPAndDrivers Questions? SUMMARY

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