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标题: [NUC980] Running UBIFS rootfs on SPI NOR Flash [打印本页]

作者: admin 时间: 4 天前
标题: [NUC980] Running UBIFS rootfs on SPI NOR Flash

NUC980 Chili Board + Linux 5.10 + Buildroot 2024

This article documents a working setup to use UBIFS as the root filesystem on SPI NOR flash (Winbond W25Q256, 32 MB) on the NUC980 Chili board.

1. Preparation

Strongly recommended: clone a fresh Buildroot repository to avoid residual kernel / rootfs artifacts inflating the image.

$ git clone https://github.com/OpenNuvoton/buildroot_2024
$ cd buildroot_2024
$ make nuvoton_nuc980_chili_defconfig

2. Buildroot Configuration (RootFS = UBIFS)

Enter Buildroot menuconfig:

$ make menuconfig

2.1 Remove RAM filesystem (initramfs)

Disable initramfs completely:

Filesystem images --->
[ ] initial RAM filesystem linked into linux kernel
[ ] cpio the root filesystem (for use as an initial RAM filesystem)

2.2 Enable UBIFS image

Enable UBIFS as the root filesystem:

Filesystem images --->

ubi image containing an ubifs root filesystem

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

Configure UBIFS with parameters matching the SPI NOR erase geometry:

Parameter

Value

Notes

Physical eraseblock size

0x10000

64 KB erase sector (W25Q256)

Sub-page size

SPI NOR has no sub-page

Logical eraseblock size

0xFF80

64 KB - UBI headers

Minimum I/O unit size

0x1

Byte-addressable

Maximum logical eraseblock count

384

~24 MB rootfs partition

Additional mkfs.ubifs options

-F

Force creation on NOR

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  --->

Partition parsers  --->
         <*> Command line partition table parsing

Enable UBI - Unsorted block images --->

UBI Fastmap (experimental feature)
SPI NOR device support --->
[ ] Use small 4096 B erase sectors

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:

File

Type

Exec Addr/Offset

uboot.bin

Loader

0xE00000

env.txt

Environment

0x80000

nuc980-chili.dtb

Data

0xA0000

uImage

Data

0x200000

rootfs.ubi

Data

0x800000

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.

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