The U-Boot command bootm then copies the kernel image into 0x10000 and the root filesystem into 0x800000 after that then jumps at the beginning of the kernel, thus creating the same situation as when QEMU starts with the -kernel and -initrd options. At run-time U-boot relocates itself to address 0x1000000, thus freeing 2MiB of memory from the start address. The images are placed at a distance of 2MiB, starting from address 0x10000. The following figure shows the solution I came up with:Īt the beginning we have three binary images together: U-Boot (about 80KiB), Linux kernel (about 1.5MiB) and the root file system ramdisk (about 1.1MiB).
Linux u boot free#
The compressed kernel image size is about 1.5MiB, so the first 1.5MiB from the start address must be free and usable when U-Boot copies the kernel. This feature comes handy in our scenario because it frees lower memory space in order to copy the Linux kernel.
Linux u boot code#
One feature of U-Boot is self-relocation, which means that on execution the code copies itself into another address, which by default is 0x1000000 (16MiB). Understanding memory usage during the boot process is important because there is the risk of overwriting something during memory copy and relocation. The -kernel option in QEMU will be used to load the Flash binary into the emulated memory, and this means the starting address of the binary image will be 0x10000 (64KiB). I wanted to recreate this same situation using U-Boot, and to keep the situation similar to a real one I wanted to create a single binary image containing the whole system, just like having a Flash on board. Then QEMU prepares the kernel arguments and jumps at 0x10000 (64KiB) to execute Linux. QEMU can load a Linux kernel using the -kernel and -initrd options at a low level, these options have the effect of loading two binary files into the emulated memory: the kernel binary at address 0x10000 (64KiB) and the ramdisk binary at address 0x800000 (8MiB). There are patches ad procedures available that can add flash support, but for now I wanted to leave QEMU as it is. QEMU has the possibility to emulate Flash memory on many platforms, but not on the VersatilePB. On power on, the core loads and runs the boot-loader, that in turn loads and runs the operating system. a Flash) containing a boot-loader and the operating system. On real, physical boards the boot process usually involves a non-volatile memory (e.g. : the Busybox-based file system created in my previous post here.zImage: the Linux kernel created in my previous post here.arm-none-eabi toolchain: can be downloaded from the the CodeSourcery ARM EABI toolchain page.Alternatively, it is compiled from U-Boot source. mkImage: can be installed with the package uboot-mkimage.
Linux u boot install#
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