[NUC980] Running UBIFS rootfs on SPI NOR Flash

2.3 UBIFS parameters for W25Q256 (SPI NOR, 32 MB)

Configure UBIFS with parameters matching the SPI NOR erase geometry:

These settings are critical. If they don’t match the flash erase size, UBIFS will fail at mount time.

3. Linux Kernel Configuration (5.10)

$ make linux-menuconfig

3.1 Remove initramfs support

General setup  --->
    [ ] Boot config support
    [ ] Initial RAM filesystem and RAM disk (initramfs/initrd) support

Kernel must not expect an initramfs since rootfs lives on SPI NOR.

3.2 Enable MTD / UBI / SPI NOR

Device Drivers  --->
    Memory Technology Device (MTD) support  --->
        

Key points:

• Command line partition parsing is required for ubi.mtd=.
• Disable 4K erase sectors – W25Q256 uses 64 KB erase blocks.
• UBI Fastmap significantly improves mount time on NOR.
  

4. Device Tree: SPI NOR Partition Layout

Edit the buildroot_2024/output/build/linux-custom/arch/arm/boot/dts/nuc980-chili.dts to define SPI NOR partitions in the DTS.

qspi0: spi@b0060000 {
    status = "okay";

    flash: flash@0 {
        compatible = "jedec,spi-nor";
        #address-cells = <1>;
        #size-cells = <1>;
        reg = <0>;
        spi-max-frequency = <30000000>;

        partition@0 {
            label = "uboot";
            reg = <0x00000000 0x00100000>;
        };
        partition@1 {
            label = "kernel";
            reg = <0x00200000 0x00600000>;
        };
        partition@2 {
            label = "rootfs";
            reg = <0x00800000 0x01800000>;
        };
    };
};

5. U-Boot Environment (env.txt)

Create a env.txt file with the following contents:

baudrate=115200
bootdelay=1
stderr=serial
stdin=serial
stdout=serial
setspi=sf probe 0 30000000
loadkernel=sf read 0x7fc0 0x200000 0x600000
loaddtb=sf read 0x1800000 0xA0000 0x10000
bootcmd=run setspi;run loadkernel;run loaddtb;bootm 0x7fc0 - 0x1800000
bootargs=noinitrd ubi.mtd=2 root=ubi0:rootfs rootfstype=ubifs rw console=ttyS0 rdinit=/sbin/init mem=64M

Notes

• ubi.mtd=2 → rootfs is partition@2
• noinitrd → mandatory
• root=ubi0:rootfs → UBIFS volume name
• Kernel loads from SPI NOR, no RAM disk involved
  

6. Build and Flash Images

Build everything:

$ make

After build completes, flash the following images to SPI NOR:

7. Result

If everything is configured correctly:

• UBI attaches to mtd2
• UBIFS mounts as /
• No initramfs
• Stable rootfs on W25Q256
• UBIFS has approximately 10% to 15% additional overhead, so with 24MB of space, you'll have 20MB of usable space.