Porting Linux on Embedded Platforms

ByMeghanad ShingateElectrical Engineering DepartmentIIT Bombay

Outline

● How processor (ARM9) boots?● AT91Bootstrap overview and configuration● UBoot-1.3.4 overview and configuration● Configuring the kernel – for x86 and ARM systems● Make uImage – build kernel image● Dep, clean, mrproper● Installing kernel image - x86 systems● Porting Linux on ARM board● Editing existing drivers to adapt to your application – e.g.

SMI/MII driver

How Processor Boots (ARM9)?

● Power on● processor always boots at address 0x0● On reset processor samples jumper configuration:

○ REMAP = 0, BMS = 0 : Boot on External Memory■ Boots on slow clock (on-chip RC or 32,768 Hz)■ bootstrap (customer-programmed) does config■ To speed-up

● program PMC (main oscillator enable or bypass mode)

● program and start PLL● Reprogram SMC setup, cycle, hold, mode

timings register for CS0 for new clock● switch main clock to new value

How Processor Boots (ARM9)?

● Initialization of DBGU setial port

Internal Memories

...

...

EBI Chip select 3/ NAND Flash

...

Internal Peripherals

0x0000 0000

0x0FFF FFFF

0x4000 0000

0x4FFF FFFF

0xF000 0000

0xFFFF FFFF

Boot Memory*

ROM

...

...

0x0000 0000

0x0010 0000

0x0FFF FFFF

AT91SAM9G20EK Memory Mapping

How Processor Boots (ARM9)?

● Boot Sequence - ○ Serial (SPI) Flash Boot○ Data Flash Boot○ NAND Flash Boot○ SDCard Boot○ SAM-BA Boot - if no valid application found (waits for

USB/USART traasaction)E.g. NAND Boot

● Jump to NAND Flash Boot sequence● searches for valid application in NAND Flash - seven

valid ARM exception vectors (B-branch or LDR inst. except 6th)

How Processor Boots (ARM9)?

● If valid application found, load it into internal SRAM, perform remap and jump to 0x0 and start execution.

● Bootstrap copies uboot to RAM and start executing● UBoot gets control● UBoot initializes minimum necessory hardware● Uboot runs boot cmd and loads kernel and passes

configuration to kernel● Kernel knows hardware initialized● Kernel extracts rootfs● Kernel runs init● Init gets user space up and running

ARM Board Memory - overview

Bootstrap*

UBoot

Linux (Kernel)

rootfs.jffs2

NAND FLASH (1GB)

Maxim

Memory (Virtual)0x00000000

0x00020000

0x000A0000

0x00400000

0x22000000 (Load Addr)

0x23F00000 (Bootstrap Jump)

0x10000000 (Maxim Base)

0x11000000

} 32MB (Maxim)

SDRAM (Maxim)

SDRAM (Maxim Use)

0x113000003MB (Maxim Use)}

0x12000000} 32MB

(RAM 32+32 MB)

AT91Bootstrap

● Source and compile

$ wget ftp://www.at91.com/pub/at91bootstrap/AT91Bootstrap1.16.zip

$ unzip downloads/AT91Bootstrap1.16.zip

// Configure as per your need - see next slide

$ cd Bootstrap-v1.16$ cd board/at91sam9g20ek/nandflash$ make// Binary generated - nandflash.bin

Configuring - AT91Bootstrap

● Configure PLL, GPIO, USART, SPI○ board/at91sam9g20ek/nandflash/at91sam9g20ek.h○ board/at91sam9g20ek/at91sam9g20ek.c

#define MASTER_CLOCK 101376000 //clock (101MHz)#define PLLA_SETTINGS 0x20203F01 //PLLA#define PLLB_SETTINGS 0x10193F05 //PLLB#define IMG_ADDRESS 0x20000 //Uboot Img address in nandflash#defin IMG_SIZE 0x50000 //Img size on nand flash#define JUMP_ADDR 0x23F00000 //Final jump address(See datasheet of at91sam9g20ek for details)

● Loads Uboot in RAM and jumps to JUMP_ADDR

Uboot - 1.3.4

● Source and compile$ wget ftp://ftp.denx.de/pub/u-boot/u-boot-1.3.4.tar.bz2$ tar xjvf u-boot-1.3.4.tar.bz2$ cd u-boot-1.3.4/

// Patch$ wget ftp://www.at91.com/pub/uboot/u-boot-1.3.4-exp.5/u-boot-1.3.4-exp.5.diff$ cat u-boot-1.3.4-exp.5.diff | patch -p1

// Configure as per your need - see next sile

$ make at91sam9g20ek_dataflash_cs1_config

$ export CROSS_COMPILE=/opt/crossTools/CodeSourcery/bin/arm-none-eabi-

$ make

// Binary generated - uboot.bin

Configuring - UBoot

● Initialization - MACB, ASICs,USART etc.○ board/atmel/at91sam9g20ek/at91sam9g20ek.c

● Configuration - ○ include/configs/at91sam9g20ek.h

#include PHYS_SDRAM 0x20000000 //SDRAM

#include PHYS_SDRAM_SIZE 0x04000000 //SIZE#include CFG_NAND_BASE 0x40000000 // FLASH BASE#include CFG_LOAD_ADDR 0x22000000 // Load addr#define CONFIG_BOOTCMD "nand read 0x22000000 0xA0000 0x200000; bootm"#define CONFIG_BOOTARGS "root=1f01 rootfstype=jffs2"

Overview - Kernel Compilation

● Compiling kernel composed of configuring, building and installing

● Latest stable kernel version available is 3.3.2● We will go step-by-step over configuring, building and

installing kernel version 2.6.30● Presentation mostly will be embedded system oriented -

ARM9● Downloading kernel

$ wget http://www.kernel.org/pub/linux/kernel/v2.0/linux-2.6.30.tar.bz2

$ tar -zxvf linux-2.6.30.tar.gz

Configuration – x86 System

● Configuration can be non trivial, since you have to include support for your hardware for proper working

● If already configured – old configuration will be in .config, then do “make oldconfig”

● For new configuration do “make menuconfig”, based on your hardware go through the options and select configuration e.g. sound support, networking

● “make defconfig”, It will automatically copy your distribution's .config, that should fit almost everything

Configuration – ARM● For ARM(at91sam9) – download patch (if any, for your

architecture. Here the example is for Atmel ARM9) from $ wget ftp://www.linux4sam.org/pub/linux/2.6.30-at91-exp.patch.gz

$ zcat 2.6.30-at91-exp.patch.gz | patch -d linux-2.6.30 -p1

● For embedded system we need toolchain for cross-compilation of kernel, I have added references for the same.

$ export ARCH=arm

$ export CROSS_COMPILE=<path_to_cross-compiler/cross-compiler-prefix->

e.g.

$ CROSS_COMPILE=/opt/crossTools/arm-2007q1/bin/arm-none-linux-gnueabi-

● Then for configuration -$ make oldconfig //OR

$ make menuconfig

Menuconfig

● Select options using spacebar● Use Enter key to see sub-menus● Save and exit

Configuring - Linux

● Board Init - I2C, SPI, USB etc.○ arch/arm/mach-at91/board-sam9g20ek.c

at91sam9260_initialize(18432000) //18.432 MHz

● Nand flash partitions

Building - Linux

● For x86 system-$make dep – creates dependencies$make bzImage – creates kernel image$make modules – builds components chosen to build as

modules● It will generate kernel image - /arch/i386/boot/bzImage● For ARM building kernel image-

○ If has Uboot - $make uImage○ If do not have Uboot - $make zImage

It will generate kernel image - /arch/arm/boot/u(z)Image

dep, clean, mrproper

● Make dep – generates dependency information which then used for building the kernel

● Sometimes you might need to clean up the source and build all again, make clean will remove all object files.

● Make mrproper removes everything except source, it will also remove .config* files, so be sure to save configuration elsewhere.

● For building first time you only need make dep, make clean and make mrproper not needed.

Installing new kernel - x86

● $sudo make modules_install – installs modules in /lib/modules/2.6.30

● $sudo make install – installs kernel in /boot/● $ sudo update-initramfs -c -k 2.6.30 – temporary file

system used in boot process.● $ sudo update-grub – lets bootloader know new kernel● Verify new kernel installation

○ See kernel image in /boot (here vmlinux-2.6.30)○ See whole new directory of loadable modules under

/lib/modules (here 2.6.30)● Reboot ! (and pray!)

Porting Linux - ARM board

● Porting of new kernel on ARM board differs from board-to-board.

● We have - bootstrap, uboot, linux kernel, rootfs● Atmel SAM-ICE (JTAG) - used to put bootstrap and uboot

on flash (see reference for HowTo)● JTAG software tool - SAM-BA● Bootstrap - initialize access, copy uboot to RAM● Uboot - (0x20000)

○ Read/write flash memory○ Use the network: IP config, telnet, ping, tftp○ Probe hardware or perform dignostic○ Boots kernel

(reboot board and use serial terminal for next steps)

Porting Linux - ARM board

● Rootfs - use tftp (0x400000)○ Stored rootfs on flash and used as root filesystem -

JFFS2● Linux kernel - use tftp (0xA0000)

○ loads rootfs○ runs Init

UBoot> set ipaddr 10.107.48.61

UBoot> set serverip 10.107.48.120

UBoot> set bootfile <binary_name_on_server>

UBoot> tftp // this will transfer file to board RAM and shows load_addr

UBoot> nand write <load_addr> <write_addr> <size_of_file>

// reboot board

Edit drivers to adapt to your application

● For each time you need not to write new driver for your application. You can adapt existing driver to meet your application requirement.

● Ioctl – I/O control library call – interaction with device drivers.

● Ioctl call - int ioctl(int, int, ...) - first arg is file discriptor to device file, second argument is Identification number of specific request to ioctl.

● Additional arguments are optional – usually ioctl has 3 arguments, third is pointer to structure.

● See references for more information on ioctl

Edit drivers to adapt to your application● Example SMI/MII driver

○ For user to implement own ioctl Linux provides identification numbers – SIOCDEVPRIVATE you can use it to implement your desired functionality.

○ smi/mii driver can be fount in drivers/net/phy/phy.c, you can add new switch statement in phy_mii_ioctl() function and do what you want.

Edit drivers to adapt to your application

● Calling ioctl from application program.

Thank You !

References

● Cross-compilation toolchain:○ http://wiki.debian.

org/BuildingCrossCompilers#Installing_a_Cross_Compiler○ http://askubuntu.com/questions/65630/installing-gnu-arm-

toolchain○ http://maxim.org.za/links.html○ https://sourcery.mentor.com/sgpp/lite/arm/portal/subscription?

@template=lite○ http://www.ibm.com/developerworks/linux/library/l-arm-

toolchain/#resources○ http://ferryzhou.wordpress.com/2011/06/30/e-couldnt-find-

package-gcc-arm-linux-gnueabi/○ http://www.gnuarm.com/○ http://www.gnuarm.com/files.html

References

● Ioctls○ http://www.linuxjournal.com/article/6908○ http://www.makelinux.net/ldd3/chp-6-sect-1

● ARM Linux boards○ http://elinux.org/BeagleBoard#U-Boot○ http://www.elinux.org/ARMCompilers○ http://elinux.org/BeagleBoardBeginners

● SAM-ICE○ http://www.atmel.com/tools/ATMELSAM-ICE.aspx?

tab=documents

References

● Uboot○ include/autoconf.mk - contains all configs.

● AT91Bootstrap○ http://www.at91.

com/linux4sam/bin/view/Linux4SAM/AT91Bootstrap

● Complete references○ http://howto.homelinux.com/wiki/Linux4SAM○ http://www.cmtekchina.com/doc/9260-boot.html

Backup Slides

Embedded boot process - brief

● Power on● Bootstrap copies uboot to RAM and start executing● UBoot gets control● UBoot initializes minimum necessory hardware● Uboot runs boot cmd and loads kernel and passes

configuration to kernel● Kernel knows hardware initialized● Kernel extracts rootfs● Kernel runs init● Init gets user space up and running