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Porting Embedded Linux and Android to your Hardware
Marcel ZiswilerNoser Engineering AG
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ContentsContents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
● Get to know your hardware
● Tools making up your development environment
● Porting embedded Linux● Porting the boot loader● Porting the embedded Linux kernel
● Introducing Android
● Porting Android● Porting the Android Linux kernel● Porting the file system with the Android framework
and its applications
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Get to Know your Hardware
What are the key components?Where to get more information?
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● Most embedded HW centred around System On Chip (SoC)
● Important to understand bus/chip mapping● What chips hooked up to what buses:
AC97, I2C, PCI, peripheral, SDRAM controller, SPI, USB bus● Bus width vs. chip width● Address pin used for command/data FIFO switching● Bus timing: SRAM vs. VLIO modes● Specialities like address offsets (shifts) or latches/multiplexing
● GPIO/interrupt routing● Most SoCs have at least partially re-configurable pins● Usually completely board specific
● Displays: number of colour data lines vs. bits per pixel (bpp)
What are the Key Components?Contents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
5
● SoC: Marvell XScale PXA320 at 806 MHz● Memories
● Volatile: 128 MB Hynix, Micron or Qimonda Mobile DDR RAM on 32 bit (2 x 16 bit chip) EMPI SDCS0
● Non-volatile: 1 GB Hynix or Samsung NAND Flash on 8 bit ND_CS0
● Ethernet: Asix AX88796BLF on 16 bit SRAM CS2, FIFO on ADDR11, address shifted by 1, interrupt GPIO36
● Audio codec/touch: NXP UCB1400E on AC97, interrupt GPIO4_2 ● Power management: Maxim MAX8660 on power I2C addr 0x34● Display/touch:
Sharp LQ043T3DX02 4.3” WQVGA, 480 x 272, 16 or 18 bpp
Colibri XScale PXA320
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● Marvell XScale PXA320 at 806 MHz● Memories
● Volatile: 128 MB Hynix, Micron or Qimonda Mobile DDR RAM on 32 bit (2 x 16 bit chip) EMPI SDCS0
● Non-volatile: 1 GB Hynix or Samsung NAND Flash on 8 bit ND_CS0
● Unfortunately no Ethernet● Audio codec/touch: Wolfson WM9713L on AC97, interrupt
GPIO36● Power management: Maxim MAX8660 on power I2C addr 0x34● Fuel gauge: Ti Bq27210 on I2C addr 0x55● Display/touch: Hitachi TX09D40VM3CAA, 240 x 320, 16 bpp
Limestone PDA Design Kit
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● Study Data Sheets and User Guides● From some vendors freely available on-line● Other vendors including Marvell and Samsung require you to
sign an NDA
● Source-code of other similar HW might be of help as well
● Ask questions on relevant mailing lists● U-Boot: [email protected]● Linux kernel: [email protected]● Subsystem specific ones for e.g. MTD, YAFFS2, USB, ...
● Lots of experience of course
Where to get more Information?Contents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
8
Tools making up your Development Environment
How to low-level control your hardware?
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● Most SoCs feature some low-level HW debugger interface● Background debug mode (BDM) found on ColdFire/PowerPC● Different joint test action group (JTAG) IEEE 1149.1 variants● Nexus IEEE-ISTO 5001-2003
● XScale feature standard ARM EJTAG interface● Interfacing usually requires special pod called a HW JTAG
debugger
How to low-level control your HardwareContents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
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● Abatron BDI2000/BDI3000● The one used by the pros● Dependable technology even if in doubt about your HW/SW● Ethernet interface● Telnet command line interface● Direct GDB remote debug interface (RDI) support● Directly burn NOR flashes● No direct NAND flash support● Start-up script loaded by TFTP
● Low-level memory read/write operations● Set SDRAM controler registers to initialise and calibrate DDR
● Image loading by TFTP
Hardware JTAG Debugger
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● OpenOCD with e.g. Amontec JTAGkey-Tiny● The one used by the diys● Open-source JTAG debugger solution● No support for latest PXA3xx chips, but works for PXA270● Slightly sluggish, but hey, costs 100 times less!
Hardware JTAG Debugger (cont.)
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Porting Embedded Linux
Porting the boot loaderPorting the embedded Linux kernel
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Porting the Boot Loader
What is supported by open-source?How to boot from NAND flash?
How does the low-level initialisation work?Is there a run-from-RAM U-Boot variant?
How to use U-Boot's nand_spl framework?
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● U-Boot boot loader● Clone git repository● Configurations in include/configs show various PXA variants
like PXA250 and PXA27X to be supported● No mentioning of PXA3xx● cpu/pxa/cpu.c shows Monahans (code name for PXA3xx)
support● Two supported boards: Delta and Zylonite● Zylonite being Marvell's development board
● Pick existing board close to your HW and go from there● I took zylonite as base of my porting efforts
What is supported by Open-Source?Contents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
15
● What features should be supported?● Primary task: boot board● Serial debug console a must● Image loading via Ethernet/USB is convenient
● What about the boot concept?● What is the boot media? My HW only features NAND flash
● First get booting from initialised SDRAM via debugger working● BDI initialises SDRAM● Load special run-from-RAM U-Boot image to SDRAM● Directly execute re-located U-Boot from there● Allows for quick development cycle and easy debugging
PortingContents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
16
● Booting from NAND flash is not as trivial as booting from NOR● NOR
● Supports eXecute in place (XIP)● NAND
● Usually no XIP support● Requires special provisions for NAND booting built into SoC
● PXA3xx features mask programmed initial program loader (IPL)● Fetches first NAND block containing your secondary program
loader (SPL) into internal SRAM to be executed● SPL to initialise enough from boards memories (e.g. SDRAM)
plus NAND controller to continue booting● U-Boot NAND boot framework called nand_spl only for PowerPC
based SoCs
Booting from NAND FlashContents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
17
● lowlevel_init.S● Written in assembly● Called by generic PXA SoC boot code cpu/pxa/start.S● Configure minimal set of GPIO pins mainly for serial console● Your board might use completely different mapping● Initialise chip select registers● Initialise static memory controler● Initialise dynamic memory controler
● Calibrate DDR memory timing
Low-level InitialisationContents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
18
● Skip DDR RAM initialisation● Already done by BDI start-up script
● Skip relocation to RAM● Already running from RAM
● Skip clock configuration● Changing it mid-ways completely screws the game
● Configure working environment area● NVRAM variant pointing to some arbitrary location in RAM
works just fine for now● Should give you the first U-Boot prompt!
Run-from-RAM VariantContents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
19
● Working NAND flash driver as pre-requisite● Zylonite board support contained bare bones NAND driver● Only supports SW ECC generation● PXA3xx NAND controller features HW ECC generation● Marvell's IPL requires HW ECC algorithm and OOB placement● Adding HW ECC glue logic showed timing issues on write● Short delay in write routine did the trick
NAND BootingContents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
20
● Symbolic links to a few vital source files scattered throughout U-Boot
● Starts with cpu/pxa/start.S● Continues with our board's lowlevel_init.S● Ends up in generic nand_spl/nand_boot.c● Paired with our NAND driver● As few as possible other files
● cpu/pxa/interrupts.c featuring delay implementation● drivers/nand/nand_ecc.c for ECC glue● lib_arm/interrupts.c for exception handling● _udivsi3.S for division implementation
nand_spl FrameworkContents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
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● Tricky part: trimming to fit into 16 KB of first NAND block● Just define away bloated stuff
● E.g. printf as SPL anyway won't be able to output anything● Generic nand_boot.c required significant modifications
● Supported only directly bus/pin controlled NAND chips● PXA3xx feature intelligent NAND controller
● Some rather tricky debugging of the different boot stages● Finally booting from NAND!● Ethernet similar to existing PXA270 HW just on 16 bit rather than
32 bit peripheral bus● Unfortunately final HW features different components
● Large block rather than small block NAND chip● New Ethernet controller
nand_spl Framework (cont.)Contents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
22
● New NAND chip● Bigger page size of 2 KB rather than 512 bytes● Large blocks of 128 KB rather than 16 KB
● Attempts to play nice with existing U-Boot NAND driver and MTD infrastructure failed!
● Somebody ported later Linux MTD subsystem to U-Boot● Paved the way for large block NAND support
● Ported Linux' latest PXA3xx NAND driver pxa3xx_nand.c to U-Boot● Implementing polling operation
Getting Production HW to workContents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
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● New Ethernet chip● Still NE2000 compatible● Hooked up differently
● Switching between command and data FIFO by address 11 rather than 2
● Required different VLIO bus timing● Chineese blog outlined integration into ancient U-Boot version
● Could not read a single comment of this blog● But managed to port code snippets to latest U-Boot
Getting Production HW to work (cont.)Contents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
24
Porting the Linux Kernel
What is supported by open-source?
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● Embedded Linux kernel● Clone git repository● Configurations in arch/arm/configs show various PXA variants
including PXA3xx to be supported● PXA support can be found in arch/arm/mach-pxa● Multiple supported boards: CM-X300, Littleton and Zylonite● Littleton and Zylonite being Marvell's development kits/boards
What is supported by Open-Source?Contents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
26
● At first no mainline PXA3xx support● Had to go with NDAed Marvell kernel being slightly out-dated
● Got it built for Zylonite development platform● Did not boot or rather at least not output anything
● Had to modify pin configuration for console UART again● Board specific code in arch/arm/mach-pxa/zylonite.c
● U-Boot still without Ethernet TFTP capabilities● Pre-load it all by BDI
● U-Boot to address 0x83008000● Linux kernel to address 0x81000000● 16 MB RAM disk to address 0x87000000
● First Linux shell!
The early AttemptsContents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
27
● While working on U-Boot PXA3xx support hit mainline● New XScale multi function pin (MFP) framework● GPIOlib
● PXA support located at arch/arm/mach-pxa● Zylonite support split into multiple files
● zylonite.c for generics● zylonite_pxa300.c zylonite_pxa320.c
for SoC specific configuration/initialisation● Similar to our HW coming in two flavours
● High-end PXA320 with audio and touch● Low-cost PXA300 without audio and touch
● Different pin numbering and peripheral support
Porting Linux KernelContents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
28
● MFC configuration table● Outlining exact use of each pin
● Particular peripheral block● General purpose IO (GPIO)
● Macros from mach/mfp-pxa300.h resp. mfp-pxa320.h● By no means comprehensive● For all possible combinations consult Marvell's user guide
● Possible to tri-state pins● Configure as GPIO input or null alternate function● Required on Colibri due to multiple SoC pins being routed to
identical module pin
SoC specific CodeContents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
29
● SoC specific peripherals● AC97 audio● Touch screen controller● NAND flash partitioning due to different sized chips
● Main initialisation functions● Check whether running on respective SoC● Configure pins according to our MFP configuration tables● Register SoC specific peripherals● Assign GPIO pins and NAND flash partitions used in generic
code
Porting Linux Kernel (cont.)Contents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
30
● Handle chip select address mapping● Utilises CPLD for flexibility reason● Configure peripherals available on all module types
● Ethernet● Frame buffer with display configurations● MMC/SD card controller● NAND flash controller● RTC chip● SPI controller● USB controller
Generic CodeContents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
31
● Generic initialisation function first calls specific ones
● Enable chip select address decoder
● Configure and register generic peripherals
● Defines actual machine structure
Porting Linux Kernel (cont.)Contents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
32
Introducing Android
What is Android?How about its Architecture?
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●Open-source mobile phone platform initiated by Google● Building a better phone for consumers● source.android.com
●Open handset alliance● Several companies innovate in the open● …Increased openness will enable everyone in our industry to
innovate more rapidly and respond better to consumer's demands. …
● openhandsetalliance.com
●Noser Engineering AG works on core functionality
Contents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
34
Android ArchitectureContents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
35
Porting Android
What are the system requirements?How to port the Android Linux kernel?
How to port the file system with the Android framework and its applications?
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● Recent Linux kernel running on your target HW
● ARM based SoC● Low-level assembly optimisation● Code generation in graphics subsystem
● 128 MB SDRAM
● 256 MB flash favourably of the NAND kind
● Optimised for 16 bpp QVGA LCD with capacitive touch screen
● At least 5 button navigation keypad
System RequirementsContents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
37
● What we got so far● Android 1.0 kernel based on vanilla Linux 2.6.25● Colibri BSP kernel based on vanilla Linux 2.6.26
● Two possibilities● Port Android modifications into our BSP kernel● Or vice versa
● Depending on who did your BSP that code might be better
understood by you speaking for second approach
● Android modifications rather well integrated/understood
● Analyse Android kernel modifications and integrate them into our
BSP kernel
Porting Android Linux KernelContents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
38
● Ashmem● mm/ashmem.c● Anonymous shared memory subsystem● Allow processes to share named blocks of memory● Kernel may reclaim them if not in use
● Binder IPC● drivers/android/binder.c● System oriented component architecture● Providing object-oriented operating system environment● Inter-process communication (IPC) between processes and
thread pools● Memory management and clean-up functionality
Android Kernel ExtensionsContents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
39
● Logger● drivers/android/ram_console.c
● Store kernel log messages in RAM buffer● drivers/android/logger.c
● Logging mechanism for user processes to read and write system log messages
● Low Memory Killer● drivers/misc/lowmemorykiller.c● Scans list of running processes and kills one● Optional component not required for basic bring-up
Android Kernel Extensions (cont.)Contents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
40
● Power management● drivers/android/power.c● At its core uses regular Linux power management subsystem● Does not poll for power related changes● Uses iNotify interface via fs/inotify_user.c● Subscribe to power related updates
● YAFFS2● Yet another flash file system 2nd edition● fs/yaffs2/*● Primary file system for low-cost high density NAND flash based
storage● Not part of any mainline kernel yet
Android Kernel Extensions (cont.)Contents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
41
Android Kernel ConfigurationContents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
● Requires one to enable previously discussed features
● Standard Android kernel configuration (emulator)
arch/arm/configs/goldfish_defconfig
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Special ConsiderationsContents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
● Frame buffer● Requires double buffering aka panning functionality● Allocate twice the memory required for actual frame size● Pan function selects which part is actually output to screen
● Touch screen● Android uses standard Linux input subsystem● Driver that not only reports pressure but button touch as well
● BTN_TOUCH upon detecting pen down event● Many mainline touch drivers do not implement it that way
● drivers/input/touchscreen/ucb1400_ts.c● drivers/input/touchscreen/wm97xx-core.c
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Porting the File System with the
Android Framework and its ApplicationsContents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
● Initial RAM file system to boot-strap Android● Regular gziped cpio archive as initramfs● Contains just Android proprietary init process
● 3 different flash partitions● Each 64 MB in size● YAFFS2 NAND flash file system● System partition required to be pre-loaded● User data partition● Cache partition
Image File MTD Partition Mount Point
ramdisk.img N/A /
system.img /dev/mtdblock0 /system
userdata.img /dev/mtdblock1 /data
N/A /dev/mtdblock2 /cache
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Touch Screen CalibrationContents
Get to know your Hardware
Development Environment
Porting Boot Loader
Porting Linux Kernel
Introducing Android
Porting Android
● No support for calibration as required by resistive touch screens
● Only capacitive touch screens not requiring any calibration
● Traditionally touch screen calibration handled by tslib● Special ts_calibrate application● Generates /etc/pointercal file containing calibration constants
● Integrated calibration calculation into Android● Did not bother to port actual calibration application to Android● Just integrate correct calibration file into Android file system
● /system/etc/pointercal
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Continuing Information
● Visit us at our booth at the Embedded World 2009
11-115
● Attend one of our next trainings
Embedded Linux Seminar - June 4 & 5, 2009
● Visit our website
www.noser.com/linux
● Or contact us for more information