Nokia RX-51 aka N900

The nokia_rx51_defconfig configuration file results in a u-boot.bin which can be chainloaded by the Nokia second stage bootloader (NOLO) in QEMU or on a real N900. It does very little hardware configuration because NOLO has already configured the board. It is only needed to enable the internal eMMC memory via the twl4030 regulator which is not enabled by NOLO.

make CROSS_COMPILE=arm-linux-gnueabi- nokia_rx51_defconfig u-boot.bin

NOLO is expecting a kernel image and will treat any image it finds in OneNAND as such. This u-boot is intended to be flashed to the N900 like a kernel. In order to transparently boot the original kernel, it will be appended to u-boot.bin at 0x40000. NOLO will load the entire image into (random) memory and execute U-Boot, which saves hardware revision, boot reason and boot mode ATAGs set by NOLO. Then the bootscripts will attempt to load uImage, zImage or boot.scr file from a FAT or ext2/3/4 filesystem on external SD card or internal eMMC memory. If this fails or keyboard is closed then the appended kernel image will be booted using some generated and some stored ATAGs (see boot order).

For generating combined image of U-Boot and kernel (either in uImage or zImage format) there is a simple script called u-boot-gen-combined. It is available in following repository:

To generate the combined.bin image from u-boot.bin and kernel.bin (in either uImage or zImage format) use:

sh u-boot-gen-combined u-boot.bin kernel.bin combined.bin

The original Maemo Fremantle PR1.3 zImage kernel binary is available at:

To unpack it (from DEB/AR, TAR and FIASCO) execute the following commands:

ar x kernel_2.6.28-20103103+0m5_armel.deb data.tar.gz
tar -O -xf data.tar.gz ./boot/zImage-2.6.28-20103103+0m5.fiasco > kernel_2.6.28-20103103+0m5.fiasco
0xFFFF -M kernel_2.6.28-20103103+0m5.fiasco -u

The flashed image must start with a 2 KiB NOLO!img header which contains size of the image. The header consists of the bytes NOLO!img\x02\x00\x00\x00\x00\x00\x00\x00 followed by the 4 byte little endian size of the image. The rest of the 2 KiB header just contains zero bytes.

The Nokia proprietary flasher and also the open source 0xFFFF flasher automatically prepend the required NOLO!img header and both applications expect that the image does not contain a NOLO!img header. Adding a NOLO!img header is required only in case of using the nandwrite tool for flashing.

The open source 0xFFFF flasher is available in the following repository:

It is possible to load u-boot.bin via USB to the N900 RAM and boot it without needing to flash it. This is done via 0xFFFF running on the host PC:

0xFFFF -m u-boot.bin -l -b

0xFFFF also supports flashing a kernel image either via USB or directly on N900 device. Flashing u-boot/kernel/combined image is done as:

0xFFFF -m combined.bin -f

Via 0xFFFF it is also possible to generate a standard flashable image in Nokia FIASCO format which contains metadata information like device identification (RX-51) and version string (v2021.04):

0xFFFF -m RX-51:v2021.04:kernel:u-boot.bin -g u-boot.fiasco

There is support for the hardware watchdog. The hardware watchdog is started by NOLO so U-Boot must reset the watchdog to prevent rebooting the device (but not very often, max every 2 seconds). There is also support for framebuffer display output with ANSI escape codes and the N900 hardware keyboard input.

When U-Boot is starting it sets the IBE bit in the Auxiliary Control Register, which is needed for Thumb-2 ISA support. This is a workaround for erratum 430973.

Default boot order

  1. if keyboard is closed boot automatically attached kernel image

  2. try boot from external SD card

  3. try boot from internal eMMC memory

  4. try boot from attached kernel image

Boot from SD or eMMC in this order:

  1. boot from FAT partition

    1. find boot.scr on first FAT partition

    2. find uImage on first FAT partition

    3. find zImage on first FAT partition

    4. same order for 2nd - 4th FAT partition

  2. same as 1. but for ext2/3/4 partition

Available additional commands/variables

  • run sdboot - Boot from external SD card (see boot order)

  • run emmcboot - Boot from internal eMMC memory (see boot order)

  • run attachboot - Boot attached kernel image (attached to U-Boot binary)

  • run scriptload - Load boot script ${mmcscriptfile}

  • run scriptboot - Run loaded boot script

  • run kernload - Load kernel image ${mmckernfile}

  • run initrdload - Load initrd image ${mmcinitrdfile}

  • run kernboot - Boot loaded kernel image

  • run kerninitrdboot - Boot loaded kernel image with loaded initrd image

  • run trymmcscriptboot - Try to load and boot script ${mmcscriptfile}

  • run trymmckernboot - Try to load and boot kernel image ${mmckernfile}

  • run trymmckerninitrdboot - Try to load and boot kernel image ${mmckernfile} with initrd image ${mmcinitrdfile}

Additional variables for loading files from mmc

  • mmc ${mmcnum} (0 - external, 1 - internal)

  • partition number ${mmcpart} (1 - 4)

  • partition type ${mmctype} (fat, ext2, ext4; ext2 is just alias for ext4)

Additional variables for booting a kernel

  • setup_omap_atag - Add OMAP table into atags structure (needed for maemo kernel)

  • setup_console_atag - Enable serial console in OMAP table

  • setup_boot_reason_atag - Change boot reason in OMAP table

  • setup_boot_mode_atag - Change boot mode in OMAP table

Variable setup_omap_atag is automatically set when booting attached kernel. When variable setup_omap_atag is set, variable setup_console_atag is unset and u-boot standard output is set to serial then setup_console_atag is automatically set to 1. So output from Maemo kernel would go to serial port.

UBIFS support

UBIFS support is disabled, because U-Boot image is too big and cannot be flashed with attached kernel image to RX-51 kernel nand area. For enabling UBIFS support add following lines into file configs/nokia_rx51_defconfig:


Early output

Early U-Boot output can be enabled on serial console by adding following lines into file configs/nokia_rx51_defconfig:


Note that early output is not available on USB tty console.

Verbose debug output

Verbose debug output with maximal log level can be enabled by adding following lines into file configs/nokia_rx51_defconfig:


And compiling U-Boot by additional make parameter KCPPFLAGS=-DLOG_DEBUG.

Run in QEMU

Download and compile Linaro version of qemu which contains n900 qemu machine. Source code is available in qemu-linaro git repository and the last working version is at commit 8f8d8e0796efe1a6f34cdd83fb798f3c41217ec1.

Use following commands to compile qemu-system-arm binary with n900 qemu machine support:

git clone
cd qemu-linaro
git checkout 8f8d8e0796efe1a6f34cdd83fb798f3c41217ec1
./configure --enable-system --target-list=arm-softmmu --disable-werror
make -j4
cd ..
ln -s qemu-linaro/arm-softmmu/qemu-system-arm .

Using n900 qemu machine requires proprietary Nokia qemu qflasher tool (in reality it is just generator of qemu MTD images) with first stage images (xloader-qemu.bin and secondary-qemu.bin), similar what is required on the real HW. License of flasher and images allows non-commercial redistribution and it is available at website:

wget -c
tar -xf qemu-n900.tar.gz

To generate qemu bootable MTD image mtd.img from U-Boot binary u-boot.bin and unpacked first stage images, run following command:

./qflasher -v -x xloader-qemu.bin -s secondary-qemu.bin -k u-boot.bin -m rx51 -o mtd.img

Instead of u-boot.bin binary it is possible to also used combined U-Boot + kernel binary combined.bin.

Finally, to boot mtd.img with graphics display and keyboard with optional serial console on current terminal, run:

./qemu-system-arm -M n900 -mtdblock mtd.img -serial /dev/tty

Additionally it is possible to emulate also eMMC and uSD card by appending qemu -sd arguments:

./qemu-system-arm -M n900 -mtdblock mtd.img -sd emmc.img -sd sd.img -serial /dev/tty

For more examples, look into the test/ CI testing script.