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Porting Operating Systems

Porting Operating Systems. Phan Duy Hùng (PhD) ES Lecturer – Hanoi FPT University. Content. Bootloader Kernel Filesystem Bootloader (again). Embedded Linux Introduction. Linux Support CPU: x86, ARM, MIPS, SH, i960, PowerPC, …etc Open Source Powerful Network Functions

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Porting Operating Systems

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  1. Porting Operating Systems Phan Duy Hùng (PhD) ES Lecturer – Hanoi FPT University

  2. Content • Bootloader • Kernel • Filesystem • Bootloader (again)

  3. Embedded Linux Introduction • Linux • Support CPU: x86, ARM, MIPS, SH, i960, PowerPC, …etc • Open Source • Powerful Network Functions • Easy Software Porting • GNU Complier and Debugger

  4. Bootloader • Kernel • Root Filesystem Target Cross-platform Development Environment Host Cross-Development Environment • Target has limited resource (memory, storage, low speed processor) . • Host and Target are different architecture

  5. Ways of Hardware Connection

  6. Linux Architecture Applications Bash Shell Linux Kernel hardware

  7. Linux Architecture Java Applications GUI GLIBC Other Libraries Kernel System Call Interface File System Protocol Stacks Kernel Bootloader Drivers Hardware

  8. All the things we need • Cross-Platform development toolchain • Bootloader • Usually provided by the vendor • Linux kernel • Linux kernel + some patches if needed • Filesystem • Busybox • Device node • Configuration

  9. Bootloader Concepts (cont`) • Typical space allocation

  10. Bootloader Concepts • What is bootloader ? • Load kernel and filesystem • Initialize hardware elements • Many bootloaders for each architecture • LILO and GRUB for x86 • LILO: http://lilo.go.dyndns.org/ • GRUB: http://www.gnu.org/software/grub/ • U-Boot for x86, ARM, PowerPC • U-Boot: http://u-boot.sourceforge.net/

  11. Bootloader Concepts (cont`) • Bootloader also depends on various hardware • All type CPU will execute the instructions from the defined address when power on • Normally, there exists some solid storage devices mapped to defined address • ROM, EEPROM, FLASH, etc

  12. The Bootloader's Job One main mission: load the operating system(s). Tasks: • Initialize the machine properly (the kernel can do this later too). • Access the kernel and initrd files in their storage medium (need to support the corresponding filesystem too) • Because of the above 2 tasks, bootloaders may platform specific! • Load the kernel and initrd files • Execute the kernel file with the right command line

  13. bootloader

  14. Some Bootloaders • LILO: LInux LOad. Original Linux bootloader. Still in use! • http://freshmeat.net/projects/lilo/ • Supports: x86 • GRUB: GRand Unified Bootloader from GNU. More powerful. • http://www.gnu.org/software/grub/ • Supports: x86 • LinuxBIOS: Linux based BIOS replacement • http://www.linuxbios.org/ • Supports: x86

  15. Some Bootloaders (cont.) • UBoot: Universal Bootloader. The most used on arm. • http://uboot.sourceforge.net/ • Supports: arm, ppc, mips, x86 • RedBoot: eCos based bootloader from RedHat • http://sources.redhat.com/redboot/ • Supports: x86, arm, ppc, mips, sh, m68k...

  16. Why Use Linux • Open Source • Reliability • Salability • Secure • Supports Virtually All Network Communication Protocols

  17. GCC • Cross Compiler creates executables for another platform (such as ARM), the output form can be ELF (Executable and Linking Format) • If you build a Linux Kernel, you have to use Cross Compiler, i.e. GCC for most cases

  18. GCC = GNU Compiler Collection • Features • Portable • Cross-compiling • Support different languageC, C++, Objective-C, Fortran, Java, and Ada • Free Software • Compiler: arm-linux-gcccompiling source codes to run on arm platforms $ arm-linux-gcc hello.c –o hello/usr/local/arm/include/asm,linux

  19. System Boot Flow

  20. System Storage • The storage devices used in embedded systems are often quite different from those used in workstations and servers. • Embedded systems tend to use solid-state storage devices such as flash chips and flash disks. • Need the MTD subsystem to support boot parameters root filesystem kernel bootloader

  21. Kernel Considerations Kernel Configuration Kernel Compiling

  22. Root File System Content

  23. Root File System / /bin /boot /grub /dev /etc /home /lib /mnt /proc /sbin /tmp /usr /src /bin /sbin /var /log /spool

  24. Building Root Filesystem • Download the BusyBox source code fromhttp://www.busybox.net/ • Building BusyBox • make clean • make all • make install • After make complete, the busybox will be at ./path/to/busybox_src/_install/

  25. Graphic User Interface Window System • X Window (TinyX) • http://www.xfree86.org/ • QPE (Qt Plamtop Environment) / Qtopia • http://www.trolltech.com/products/qtopia/index.html • GPE (GPE Palmtop Environment) • http://gpe.handhelds.org/ • Microwindows • http://microwindows.org/ • MiniGUI • http://www.minigui.org/

  26. Development Tools • Editor (VIM) • Toolchains

  27. Bootloader Concepts • What is bootloader ? • Load kernel and filesystem • Initialize hardware elements • Many bootloaders for each architecture • LILO and GRUB for x86 • LILO: http://lilo.go.dyndns.org/ • GRUB: http://www.gnu.org/software/grub/ • U-Boot for x86, ARM, PowerPC • U-Boot: http://u-boot.sourceforge.net/

  28. Linux-capable open source bootloaders

  29. Bootloader Concepts (cont`) • Bootloader also depends on various hardware • All type CPU will execute the instructions from the defined address when power on • Normally, there exists some solid storage devices mapped to defined address • ROM, EEPROM, FLASH, etc

  30. Bootloader Concepts (cont`) • Typical space allocation

  31. Bootloader Concepts (cont`) • Single stage or Multi-stage ? • Multi-stage bootloader can provide more complex capability and better ability to cross platform • Bootloader booted from solid storage device can be divided into two stages • Stage1 • Written by assembly language • Fast and simple • Stage 2 • Written by C • more complex capability • Easy to read and modify

  32. Bootloader Concepts (cont`) • Two operation modes • Boot loading mode (autonomous mode) • Normal working mode • Downloading mode • Bootloader can download images from host end through UART or network

  33. Bootloader Concepts (cont`) • Communication equipment and protocol • UART (Universal Asynchronous Receiver/Transmitter) and network • UART protocol: xmodem, ymodem, zmodem • slower • Network protocol: TFTP protocol • TFTP service required

  34. Bootloader’s task and structure • Stage1 and stage2 • Stage1 • Execute from flash • Copy stage2 to RAM • Stage2 • Execute from RAM • Copy kernel & Root file system to RAM • Load kernel & Root file system

  35. Bootloader’s task and structure (cont`) • Steps of stage1(according to implement order) • Hardware initialization • Prepare memory space for loading stage2 • Copy stage2 to memory • Set stack • Go to starting address of stage2

  36. Bootloader’s task and structure (cont`) • Fundamental hardware initialization • Mask all interrupts • through CPU’s interrupt mask register or state register • Set CPU speed and clock • Initialize memory • Initialize LED • Ensure hardware are initialized correctly • Initialize CPU internal instruction/data cache

  37. Bootloader’s task and structure (cont`) • Prepare memory space for loading stage2 • Determine start and end address for stage2 in RAM • Stage2_start, stage2_end • Take stack space into consideration • Stage2 is written in C • Stage2 is placed in upper part of bootloader memory space

  38. Bootloader’s task and structure (cont`) • Copy stage2 to memory • Set stack pointer (sp) • In order to execute C code of stage2 • sp points to the location before stage2 end (sp=stage2_end – 4) • Jump to the start address of stage2

  39. Bootloader’s task and structure (cont`) mem_start

  40. Bootloader’s task and structure (cont`) • Steps of stage2(according to implement order) • Initialize the hardware devices used in stage2 • Check system memory mapping • Copy kernel image and root filesystem to memory • Set boot parameters • Load kernel and root filesystem

  41. Bootloader’s task and structure (cont`) • Initialize the hardware devices used in stage2 • Initialize one UART at least • Initialize timer • Check system memory mapping • We should know which virtual memory space is really mapped to physical memory

  42. Bootloader’s task and structure (cont`) • Copy kernel image and root filesystem • Memory allocation mapping • Memory range of kernel image • Normally, locate in memory_start + 0x8000 • 0x8000 (32k) is used to store boot parameter and kernel page table • Memory range of root filesystem • Normally, locate in memory start + 0x100000 • Copy from flash

  43. Bootloader’s task and structure (cont`) • Set boot parameters • In U-boot, boot parameters are defined in the header file of target board • Boot parameters: • boot command • root device • root filesystem type • console • memory size • network configuration • etc.

  44. Bootloader’s task and structure (cont`) • Load kernel and root filesystem • Jump to memory_start + 0x8000 • CPU mode • Disable interrupts (IRQs and FIQs) • In SVC mode (supervisor)

  45. Bootloader’s task and structure (cont`) • After loading kernel • Bootloader is replaced with operating system

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