System initialisation VHDL and C System initialisation

Overview In this lecture we will look at what happens when systems power on, boot up, run an operating system and power down We will look at a standard PC configuration as a reference point We will also look at how embedded boards vary Finally, we will look at the TS-7300 boot sequence

Bring systems up and down Power on BIOS Bootloader Kernel Init /sbin/init RUNNING Shutdown Power off

Points to note On most systems the names of stages (and their function) varies For example on embedded board the BIOS is often called a BSP or Firmware Bootloaders (also called boot managers) may not exist, the operating system may boot straight from BIOS The running system may not be an OS as we know it.

BIOS/BSP/Firmware From power on the system must get itself together from scratch (hence boot loading) The first part of booting will not use all of the systems resources Memory may not be configured Memory management/protection will be off Most devices will be inactive The first thing that the BIOS must do is set up memory and a run time environment.

BIOS initialisation Execute CPU bootstrap code CPU initialisation CPU Flash EEPROM ROM Copy the BIOS to RAM BIOS RAM Execute BIOS Initialise Devices

BIOS checks The BIOS will do a series of check on booting Before it starts fully running the CPU it check over i2c if the power management systems are running It won’t continue if the fan isn’t working for example It will check various devices Memory, Keyboard, mouse, media (HDD, CDROM, etc) Some may cause system failure

BIOS handover If the BIOS checks have been successful then the BIOS will attempt to execute the Bootloader (on some systems it may just go to an OS) The bootloader is normally found on a number of devices Floppy disc Hard disc CDROM Network Card Flash stick

Bootloaders These programs are used to load operating systems They allow Multi boot systems Parameters to be passed to the Operating System on boot Allows creation of initial ram discs (initrds) Recovery of Operating Systems

Bootloaders The Bootloader will be resident in the first sector of the first track of the first drive (either hard driver or floppy). This is called the MBR Master Boot Record The disc must be specially created fdisk /sys or dd on Linux All disc have MBRs but only some are active or have data in them.

Closer Look at the MBR

View of Memory over Time

Bootloaders On PC systems GRUB and, to a lesser extent, LILO are used as boot loaders On embedded boards you may not use a bootloader The Bootloaders task is to allow selection, parameterisation and execution of the OS image on disc.

The Bootloader Load Kernel into Memory Copies kernel image referenced in /etc/lilo.conffrom hard drive using BIOS services GRUB can do this or can read the file system so find a vmlinux Loads kernel image to 0x90000 (using firmware functions): 0x900000 (bootsectsector) 0x900200 (setup sector) 0x1000000 (compressed image) Jumps to label start_of_setup@ 0x90200 Alternative to bootloader–using bootsect.S

Boot time memory Compressed Image BIOS Copy of MBR Init sector Setup 0X9000 0X9020 0X1000 0X7C00 0X10000 A 5 Partition table CODE

Kernel Image Topology Building the kernel Image: User input of make zImage or make bzImage All C and assembly source files are compiled and linked into vmlinux nm vmlinux => System.map arch/i386/boot bootsect.S is assembled into bootsect.s and converted into raw binary form setup.S is assembled into setup.s and converted into raw binary form arch/i386/boot/compressed Remove .note and .comment ELF sections from vmlinux Gzip vmlinux Compile compression routines in head.S and misc.c and link into vmlinux.out arch/boot/tools/build[-b] bootsect setup system [rootdev] [> image] Concatenates bootsect, setup, and compressed/vmlinux.out into zImage

Initialize hardware Move compressed kernel Set up provisional IDT and GDT Change from real to protected mode Jump to head.S startup_32() Jump to 0x0009:0020Get system data from BIOS and generate memory map

Initialize page tables, enable paging Set-up stack (zero out BSS) Call decompress_kernel() Uncompressed kernel Uncompressing Linux…Ok, booting the kernel. Jump to start_kernel()