rpi-boot -------- A simple second stage boot loader for the Raspberry Pi to assist in the development of hobby kernels. Features -------- * Supports booting flat binary files, ELF executables and ELF and a.out executables with a Multiboot header. Linux kernels are currently not supported (but support is planned for a future version). * Supports FAT(16/32) and ext2 filesystems. * Supports loading additional modules when in Multiboot mode. * Proviedes functions to the loaded kernel to allow it to easily access the framebuffer (via a printf() interface) and the filesystem (via fopen/fread/fclose/opendir/readdir/closedir). Installation ------------ Run make in the source directory and copy the kernel.img file to the SD card containing your Raspian distribution. You are recommended to backup your original kernel.img file first. Usage ----- The rpi-boot bootloader will initially search for files called /boot/rpi_boot.cfg, /boot/rpi-boot.cfg and /boot/grub/grub.cfg (in that order) on the first partition of the SD card. If one is not found, it searches for those files on each filesystem known to the system. It understands the following commands: multiboot <kernel> [cmdline] - Load a multiboot compliant kernel module <file> [name] - Load an additional Multiboot module kernel <kernel> - Load a non-multiboot compliant kernel boot - Boot the kernel binary_load_addr <address> - Set the load address for a flat binary file subsequently loaded by the 'kernel' command entry_addr <address> - Set the entry point that is jumped to by a subsequent 'boot' command System state on kernel start ---------------------------- For Multiboot kernels, the system state is defined in MULTIBOOT-ARM, otherwise: r0 will be 0 r1 will be the ARM machine type r2 will be the address of the ATAGs (the above 3 are identical to the ARM Linux boot protocol) r3 will be the address of the multiboot_arm_functions structure as defined in MULTIBOOT-ARM. See the test-kernel directory for an example. Caveats ------- rpi-boot occupies the first 1 MiB of memory for itself. If you wish to make use of the multiboot_arm_functions functions you need to preserve this. If not you can overwrite it from within your kernel. If you do overwrite it, you should make sure you have already obtained all the information you need from the various Multiboot structures (or copied them elsewhere). Because of this, rpi-boot will not boot kernels which are linked below 1 MiB.