Transcript bootloader
LAB 8 Bootloader CS 4101 Introduction to Embedded Systems Chung-Ta King Introduction • In this lab, we will learn – What is bootloader – How bootloader works Lab 8: Compile and install bootloader Bonus Lab: Modify bootloader We have learned … • How to setup PCM-7230 environment • How to install – bootloader – linux kernel – root file system • How to execute a program on PCM-7230 Why bootloader ? • Computer processor can only execute program code found in read-only memory (ROM), random access memory (RAM). • However, modern operating systems and application program code and data are stored on nonvolatile data storage devices, such as hard drive, flash memory, DVD disc, etc. The OS and root file system have to be loaded into executable place. Why Bootloader? Cont’d • Moreover, before entering kernel, the computer must be prepared, and there are some requirements must be obeyed.[1] Kernel Booting requirements (for arm): CPU register settings r0 = 0. r1 = machine type number. r2 = physical address of tagged list in system RAM. CPU mode All forms of interrupts must be disabled (IRQs and FIQs.) The CPU must be in SVC mode. (A special exception exists for Angel.) Caches, MMUs The MMU must be off. Instruction cache may be on or off. Data cache must be off and must not contain any stale data. Devices DMA to/from devices should be quiesced. The boot loader is expected to call the kernel image by jumping directly to the first instruction of the kernel image. have to prepare computer for kernel to boot Start-up (finding bootloader) ROM Power on signal! RAM Call Reset pin Bootloader BIOS MBR (master boot record) • POST（Power-On Self Test） • Initialize devices (check IRQ/IO conflict) • Find bootloader (address) Windows file system Kernel entry Linux file system Other file system Boot sector (bootloader) Bootloader • In this lab, we use the boot-loader named iboot. • Normally, there are 2 stages in the booting sequence. RAM Bootloader Stage 1 Load Load kernel Stage 2 Root file system Bootloader • 1st stage – Usually written by assembly language. – It does some simple hardware initialization, prepares the program context for high level language, and jump to stage2. • 2nd stage – written by C language. – It does some more complex hardware initialization, detects whether a Linux kernel exists, move kernel to ram, and does some special setting for booting Linux kernel and passes the control to kernel. Memory • There are three types of memory on the PCM7230: • 1MB ROM for boot-loader: It uses AM29LV800BB-90EC Chipset. • 32MB(16MB*2) Flash for kernel and ramdisk: It uses Intel E28F128-J3A150*2 chipset. • 64MB(32MB*2) SDRAM: It uses SAMSUNG K4S561632E-TC75*2 Chipset. 0x040c0000 0x041c0000 kernel Root fs Writing Bootloader Jen255.exe i-boot LAB ASSIGNMENTS Basic Lab: Compile and install bootloader • Lab Objective – You will learn how to compile and install the IBoot bootloader in this lab. • Requirement – A build machine with Linux installed – i-boot-lite.tgz Basic Lab Steps (1/2) 1. Login provided Linux machine. 2. To build I-Boot bootloader, you need to set the PATH variable. For example, the toolchain executable files are installed in the directory /toolchain/bin, set the following environment variables: – % export PATH=$PATH:/home/pads/lab/toolchain/bin Absolute path of the executable file 3. Change into the unpacked directory and type “make”. – % cd lab/i-boot-lite – % make clean – % make Basic Lab Steps (2/2) 4. Fix the SED variable problem – To fix this problem, you need to set SED variable to be `which sed`. – % export SED=`which sed` (bash) – % make 5. Write the new compiled boot-loader to PCM-7230. – The new complied boot-loader image will be created in i-boot-lite/iboot-cerf-board-pxa250_1.7-lite.img – Rename the file to bootldr and copy it to the same folder with the utility Jen255.exe. – Now you can install the new compiled loader onto PCM-7230 as Lab 7. ＊Once you want to check the burned boot-loader, be sure you dis-connect the JTAG when using hyper-terminal. Bonus Lab : Modify Boot-loader • Lab Objective – In this lab, you will learn how to modify the bootloader codes to show some messages while booting. Bonus Lab Steps (1/2) 1. Change into the unpacked directory i-boot-lite. – % cd i-boot-lite 2. Modify the source file src/main/c_main.c. – – – – – You can use gedit src/main/c_main.c. Use itc_printf() function to show some messages. The code example is in the next page. You have to add the group info in the startup message. Ex: Group: TA 3. Compile and install the modified boot-loader as Lab 7 Bonus Lab Steps (2/2)