![]() ![]() In a standard U-Boot boot process, the bootcmd variable contains the sequence of commands to be executed automatically after the boot countdown finishes (eg, if no key is pressed). The distro boot functionality is primarily implemented as an extension of the existing U-Boot bootcmd functionality in U-Boot. Distro boot provides a framework in which these choices can be made in a predictable and platform-independent manner. That is, the first point in execution where context-aware decisions need to be made during the boot process is during the hand-off from U-Boot to the robust operating system environment. From an end-user perspective, these operations are analogous to the BIOS/UEFI experience on an x86-based platform. ![]() The BootROM then discovers the primary boot medium via a sample of the SoC's MODE pins and uses this to hand-off to the Xilinx First Stage Boot Loader or FSBL.ĭuring the runtime of the FSBL, other components such as the Xilinx-specific PMU firmware and Arm Trusted Firmware are loaded before handing off to U-Boot as the second stage bootloader. The primary way that distro boot accomplishes this goal is by decoupling the boot-time discovery of boot media from the remainder of the bootloader and firmware stack.įor example, on a Xilinx Zynq UltraScale+ platform, the initial power-on is run via the SoC's in-built BootROM. What is Distro Boot?ĭistro boot is an embedded-focused boot methodology with the primary aim to make booting Arm-based platforms more standardized and predictable similar to the experience on x86-based desktop and server platforms. These inconsistencies quickly escalate into increased development time and maintenance costs for the software teams involved. Supporting all these unique Arm platforms can be tedious at best and at worst quickly devolves to inconsistencies in the expectations and experiences on each. By contrast, the number of Arm-based SoC platforms numbers in the dozens and virtually every SoC has some form of unique boot process. While x86-based platforms have a de facto standardization of how boot operates from BIOS/UEFI during initial power-on until hand-off to a robust operating system like Linux or Microsoft Windows, this is largely incidental and has much to do with the limited number of x86-based vendors in the market. 3.4.2 Modifying an Existing /boot.scr File.3.1 Using the bootcmd Variable for Distro Boot.
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