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Step 2: boot sequence, clock system, memory and serial interface A typical embedded Linux boot-up sequence runs as follows: 1) Bootloader firmware (U-Boot in the example project) runs on the target from integrated Flash (no external memory is required) and performs all required initialisation after power-on/ reset, including setting up serial ports and the memory controller for external memory (RAM) accesses. 2) U-Boot may relocate the Linux image from external Flash to external RAM, and passes control to the kernel entry point in RAM. The Linux image can be compressed to save Flash storage space, at the cost of decompression time during boot-up. 3) Linux proceeds to boot up and mount a RAM-based file system (initramfs) as a root filesystem. Initramfs is populated with the required files and directories at build time, and is then simply linked into the kernel. 4) Execution of /sbin/init under the Linux kernel. The /sbin/init program initialises the system following the description in the / etc/inittab configuration file. 5) Once the init process completes the run-level execution and the commands in /sbin/init, it will start a log-in process. 6) The boot-up process finishes with the execution of the Smart electronic solutions – from design to finished products Cicor is a leading international high-tech industrial group active in advanced microelectronics, substrates and electronic solutions. The group offers complete outsourcing services and a broad range of innovative technologies, electronics and a wide range of production options from PCB assembly, system assembly, box-building, toolmaking and plastic injection molding. With 11 production sites and more than 20 representative offices worldwide, thegroup supplies high-quality custom-made solutions to its clients worldwide. cicor.com loads the operating system to the board. It also provides source code for the kernel and device drivers (see figure 1). Fig. 1: the main components of the Emcraft BSP for the STM32F429 Discovery board Europe Advanced Microelectronics & Substrates T +41 32 843 05 00 info-europe@cicor.com Electronic Solutions T +41 71 913 73 73 info-europe@cicor.com America Cicor Americas Ltd. T +1 617 576 2005 info-americas@cicor.com Asia Cicor Asia Pte Ltd. T +65 6546 16 60 info-asia@cicor.com Head office T +41 43 811 44 05 info@cicor.com www.electronics-eetimes.com Electronic Engineering Times Europe March 2015 21


EETE MAR 2015
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