[OpenWrt-Devel] Changes in support for Mikrotik RB493G

Mathias Kresin dev at kresin.me
Wed Dec 12 11:07:31 EST 2018

09/12/2018 21:44, W. Michael Petullo:
> Changes in the last year or so have left me a little confused with the
> OpenWrt support for the Mikrotik RB493G. I generally compile my kernels
> and root disk images myself, namely by running "make menuconfig" and
> "make" in an OpenWrt source tree. I then go on to install the built
> artifacts by booting my router using TFTP and so on.
> First, it seems that OpenWrt master has dropped YAFFS support. I cannot
> find a clear statement on this, but I also cannot find how to build an
> OpenWrt image that supports YAFFS.

kernel2minor was introduced to get rid of YAFFS [0]. It adds the YAFFS 
magic to the kernel binary, which is required by the bootloader to 
locate the kernel on flash[1].

> Because of this, I rely on an old
> openwrt-ar71xx-nand-vmlinux-initramfs.elf which does contain YAFFS
> support to install a kernel. /dev/mtdblock5 contains the kernel, and
> this device bears a YAFFS filesystem on my Mikrotik RB493G.
> How am I to install a kernel after booting a current
> openwrt-ar71xx-nand-vmlinux-initramfs.elf when there is no YAFFS support?

Aren't you supposed to load any of the nand-*-initramfs-kernel.bin? The 
initramfs-lzma.elf is some legacy image build code leftover.

> Second, things are configured to use UBIFS for the root filesystem. I
> have figured out how to set this up, but it seems rather involved:
> 1. Extract openwrt-ar71xx-mikrotik-device-nand-64m-rootfs.tar.gz on my
> build host, and use mkfs.ubifs on my build host to produce an UBIFS from
> its contents.
> 2. On the router, run ubinize, ubidetach, and ubiformat to install the
> UBIFS on /dev/mtd6.
> I suppose I am surprised that the OpenWrt build process does not build
> an UBIFS image as it does with tar.gz, ext4, and squashfs images. Am I
> missing something?

Indeed, an ubinized image - which can be written to flash using the mtd 
command - is missing.

Instead of adding such an image, I would like to propose another - 
hopefully easier - method to get OpenWrt installed on mikrotik nand boards.

Would you please give the mikrotik branch from my staging tree[2] a try. 
The commands required are mentioned in the commit message. Be aware, due 
to lack of hardware it's not runtime tested.


[0] https://git.openwrt.org/17ee6bb8f3
[1] https://git.io/fpHJx
[2] https://git.openwrt.org/?p=openwrt/staging/mkresin.git

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