I'm trying to boot Linux from U-boot on an embedded ARM board using a filesystem on a remote machine served via NFS. It appears that the ethernet connection is not coming up correctly, which results in a failure to mount the NFS share. However, I know that the ethernet hardware works, because U-boot loads the kernel via TFTP.How can I debug this? I can try tweaking the kernel, but that means recompiling the kernel for every iteration, which is slow. Is there a way that I can make the kernel run without being able to mount an external filesystem?
Debugging ethernet before NFS boot
linux;kernel;embedded;nfs;debugging
You can compile a initrd image into kernel (General Setup -> Initial RAM filesystem and RAM disk (initramfs/initrd) support -> Initramfs source file(s)). You specify file in special format like (my init for x86):dir /bin                                    0755 0 0file    /bin/busybox                        /bin/busybox    0755 0 0file    /bin/lvm                        /sbin/lvm.static0755 0 0dir /dev                                    0755 0 0dir /dev/fb                                 0755 0 0dir /dev/misc                               0755 0 0dir /dev/vc                                 0755 0 0nod /dev/console                                0600 0 0    c  5   1nod /dev/null                               0600 0 0    c  1   3nod /dev/snapshot                               0600 0 0    c 10 231nod /dev/tty1                               0600 0 0    c  4   0dir /etc                                    0755 0 0dir /etc/splash                             0755 0 0dir /etc/splash/natural_gentoo                      0755 0 0dir /etc/splash/natural_gentoo/images                   0755 0 0file    /etc/splash/natural_gentoo/images/silent-1680x1050.jpg  /etc/splash/natural_gentoo/images/silent-1680x1050.jpg  0644 0 0file    /etc/splash/natural_gentoo/images/verbose-1680x1050.jpg /etc/splash/natural_gentoo/images/verbose-1680x1050.jpg 0644 0 0file    /etc/splash/natural_gentoo/1680x1050.cfg        /etc/splash/natural_gentoo/1680x1050.cfg        0644 0 0slink   /etc/splash/tuxonice                    /etc/splash/natural_gentoo              0755 0 0file    /etc/splash/luxisri.ttf                 /etc/splash/luxisri.ttf                 0644 0 0dir /lib64                                  0755 0 0dir /lib64/splash                               0755 0 0dir /lib64/splash/proc                          0755 0 0dir /lib64/splash/sys                           0755 0 0dir /proc                                   0755 0 0dir /mnt                                    0755 0 0dir /root                                   0770 0 0dir /sbin                                   0755 0 0file    /sbin/fbcondecor_helper                 /sbin/fbcondecor_helper                 0755 0 0slink   /sbin/splash_helper                 /sbin/fbcondecor_helper                 0755 0 0file    /sbin/tuxoniceui_fbsplash               /sbin/tuxoniceui_fbsplash               0755 0 0file    /sbin/tuxoniceui_text                   /sbin/tuxoniceui_text                   0755 0 0dir /sys                                    0755 0 0file    /init                           /usr/src/init   0755 0 0I haven't used it on ARM but it should work. /init is file you are can put startup commands. Rest are various files needed (like busybox etc.).