Embedded Linux By Gus Wirth

What makes it embedded? ● Rather nebulous, line has blurred over the years ● Limited purpose ● Small resources compared to regular system, e.g. no hard drive, MB vs GB of RAM ● Limited user interface, for example no monitor or keyboard

Things an embedded system may have not seen in a regular PC ● General Purpose Input/Output (GPIO) ● Inter-Integrated Circuit (I2C) bus ● Serial Peripheral Interface bus ● Controller Area Network bus ● Watchdog timers ● Analog/Digital and Digital/Analog (A/D and D/A) converters

Where do you find embedded Linux? ● Routers ● TV set top boxes ● Media players ● Industrial Control ● Home Automation ● Cell Phones

Embedded Platforms ● MIPS ● ARM ● x86

Making Linux embedded ● Remove everything that you don't absolutely need ● Kernel – minimalist, compress with LZMA (Lempel-Ziv-Markov chain algorithm) ● uLibc or dietLibc ● Use small, alternative commands/utilities ● Busybox – Most command commands/utilities ● dnsmasq -DNS and DHCP ● dropbear - SSH

● Filesystems ● SquashFS – compressed filesystem ● JFFS2 – Journaled Flash File System uses mtd (memory technology device) driver designed for direct use with flash memory (EEPROM) Making Linux embedded (cont)

Embedded Linux distributions ● Debian ● Angstrom Linux distribution.orghttp:// distribution.org ● OpenWrt

Building a new firmware ● Get the tools a.k.a tool-chain ● Cross-compilers ● Assemblers ● Compression utilities ● File utils ● Misc utils ● Design your image ● Get source code ● Configure and compile code for target

Building a new firmware ● Assemble compiled code into firmware image ● Install firmware into target

Building a new firmware ● De-brick and try again

Building firmware with OpenWrt ● Check out OpenWrt source code ● Run “make menuconfig” ● Select platform and options ● Run “make” ● Install firmware into target ● Reboot embedded system

What makes OpenWRT so good for embedded systems? ● Someone else has done all the work ● OpenWrt does everything for you -downloads and compiles full tool chain plus firmware sources, builds and assembles images ready for installation ● Large number of supported platforms ● Paid developers ● Active community ● Good bug tracking

What makes OpenWRT so good for embedded systems? (cont) ● Package system (opkg) – only install what you want, allows installation of new/updated packages without re-imaging entire system ● Large number of packages

Demo Examples ● Ubiquiti Bullet2 ● SoC Atheros AR2317 ● MIPS 4KC core, 180 MHz ● 4MB Flash, 16MB RAM ● Ethernet ● Serial port, 3.3V ● Built-in WiFi Atheros, uses madwifi driver

Demo Examples ● Ubiquiti RouterStation ● SoC Atheros AR7161 ● MIPS 24K core, 680MHz ● 16MB Flash, 64MB RAM ● miniPCI bus ● USB 2.0 ● GPIO ● Ethernet switch ● Serial port, 3.3V

Demo Examples ● Wiliboard WBD-111 ● SoC Cortina Systems (StorLink) Gemini SL3512 ● ARM920 core, 400MHz ● 8MB Flash, 32MB RAM ● miniPCI bus ● USB 2.0 (but no power) ● GPIO ● Ethernet ● Serial port, 3.3V

Demo: Build and install firmware ● RouterStation ● “make menuconfig” ● Select target ● Select options ● “make” ● Install with tftp ● Install package with opkg ● Monitor with serial port ● Show LED's blinken

When installs fail: De-bricking ● Procedures vary by board ● Most reasonable boards separate firmware from loader – CFE – uBoot – RedBoot ● Reset button ● boot-wait ● Serial port

JTAG – Joint Test Automation Group ● Serial data in/out at pin boundaries ● Can be used as a last resort to recover a device ● Simple parallel port cable ● May need to solder board header ● Software for common routers is Windows based