ramdisk

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本文详细介绍了如何使用BusyBox构建一个ARM架构的ramdisk，包括下载、配置、打包和在U-Boot中正确加载的过程，以及遇到的错误及解决方案。

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ramdisk

制作ramdisk

制作根文件系统命令

mkdir rootfs
cd rootfs
mkdir bin dev etc usr lib sbin proc
mkdir usr/bin usr/sbin usr/lib

busybox

wget https://busybox.net/downloads/busybox-1.33.2.tar.bz2
cd busybox-1.33.2/
make menuconfig
make
make install

busybox 配置如下

setting
    [*] Don't use /usr
--- Build Options
     [*] Build static binary (no shared libs)
     (arm-linux-gnueabihf-) Cross compiler prefix

--- Installation Options ("make install" behavior)
    (/home/eddy/myplace/rootfs) Destination path for 'make install'Destination path for 'make install'

生成ramdisk

cp -r busybox-1.33.2/example/etc rootfs/
sudo apt install genext2fs
genext2fs -b 4096 -d rootfs ramdisk
gzip -9 -f ramdisk
mkimage -n 'uboot ext2 ramdisk rootfs' -A arm -O linux -T ramdisk -C gzip -a 0x44000000 -e 0x44000000 -d ramdisk.gz  ramdiskfs.gz

kernel 配置支持ramdisk

make menuconfig
+ Device Drivers + Block devices
    <*>   RAM block device support
    (16)    Default number of RAM disks
    (4096)  Default RAM disk size (kbytes)
+ File systems
    <*> Second extended fs support
    [*]   Ext2 extended attributes
    [ ]     Ext2 POSIX Access Control Lists
    [ ]     Ext2 Security Labels

uboot启动内核加载ramdisk

setenv ipaddr 192.168.13.5
setenv serverip 192.168.13.60
setenv bootargs initrd=0x44000000,0x200000 root=/dev/ram rw init=/linuxrc console=ttyS0,115200 mem=64M;tftp 0x42000000 uImage;tftp 0x44000000 ramdiskfs.gz;tftp 0x45000000 sun8i-r40-tcu1200j.dtb
bootm 0x42000000 0x44000000 0x45000000

ramdisk不识别

Wrong Ramdisk Image Format Ramdisk image is corrupt or invalid

mkimage -n 'uboot ext2 ramdisk rootfs' -A arm -O linux -T ramdisk -C gzip -a 0x44000000 -e 0x44000000 -d ramdisk.gz  ramdiskfs.gz

RAMDISK: Couldn’t find valid RAM disk image starting at 0.

原因是bootm kernel_addr rootfs_addr dtb_addr中rootfs_addr被解压后的kernel覆盖

bootm 0x42000000 0x43000000 0x44000000
改为
bootm 0x42000000 0x44000000 0x45000000