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Apache NuttX RTOS for Pine64 Ox64 64-bit RISC-V SBC (BouffaloLab BL808)
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README.md

Apache NuttX RTOS for Pine64 Ox64 64-bit RISC-V SBC (BouffaloLab BL808)

Will Apache NuttX RTOS boot on Ox64 BL808?

Let's examine the Linux Kernel Image for Ox64, and we replicate the same format for NuttX.

We download...

From the latest Ox64 Linux release...

Unzip and mount the SD Card Image.

→ ls -l /Users/Luppy/ox64/sdcard-pine64_ox64_full_defconfig     
total 25744
-rwxrwxrwx@ 1 Luppy  staff  13154816 Mar  6  2023 Image
-rwxrwxrwx@ 1 Luppy  staff      4012 Mar  6  2023 bl808-pine64-ox64.dtb
-rwxrwxrwx@ 1 Luppy  staff      4106 Mar  6  2023 bl808-sipeed-m1s.dtb
-rwxrwxrwx@ 1 Luppy  staff       350 Mar  6  2023 boot-m1s.scr
-rwxrwxrwx@ 1 Luppy  staff       352 Mar  6  2023 boot-pine64.scr
-rwxrwxrwx@ 1 Luppy  staff       352 Mar  6  2023 boot.scr
drwxrwxrwx@ 3 Luppy  staff        96 Mar  6  2023 extlinux

Dump the Image as hex...

→ hexdump /Users/Luppy/ox64/sdcard-pine64_ox64_full_defconfig/Image | mor
e
0000000 4d 5a 6f 10 20 08 01 00 00 00 20 00 00 00 00 00
0000010 00 80 cd 00 00 00 00 00 00 00 00 00 00 00 00 00
0000020 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0000030 52 49 53 43 56 00 00 00 52 53 43 05 40 00 00 00
0000040 50 45 00 00 64 50 02 00 00 00 00 00 00 00 00 00
0000050 00 00 00 00 a0 00 06 02 0b 02 02 14 00 f0 5f 00
0000060 00 80 6d 00 00 00 00 00 3e 2a 42 00 00 10 00 00
0000070 00 00 00 00 00 00 00 00 00 10 00 00 00 02 00 00
0000080 00 00 00 00 01 00 01 00 00 00 00 00 00 00 00 00
0000090 00 80 cd 00 00 10 00 00 00 00 00 00 0a 00 00 00
00000a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

The Linux Kernel Image will begin with this RISC-V Linux Image Header...

Here are the decoded bytes...

  1. code0: Executable code

    (4 bytes, offset 0x00)

    4d 5a 6f 10

  2. code1: Executable code

    (4 bytes, offset 0x04)

    20 08 01 00

  3. text_offset: Image load offset, little endian

    (8 bytes, offset 0x08)

    00 00 20 00 00 00 00 00

  4. image_size: Effective Image size, little endian

    (8 bytes, offset 0x10)

    00 80 cd 00 00 00 00 00

  5. flags: Kernel flags, little endian

    (8 bytes, offset 0x18)

    00 00 00 00 00 00 00 00

  6. version: Version of this header (MinL MinM . MajL MajM)

    (4 bytes, offset 0x20)

    02 00 00 00

  7. res1: Reserved

    (4 bytes, offset 0x24)

    00 00 00 00

  8. res2: Reserved

    (8 bytes, offset 0x28)

    00 00 00 00 00 00 00 00

  9. magic: Magic number, little endian, "RISCV\x00\x00\x00"

    (8 bytes, offset 0x30)

    52 49 53 43 56 00 00 00

  10. magic2: Magic number 2, little endian, "RSC\x05"

    (4 bytes, offset 0x38)

    52 53 43 05

  11. res3: Reserved for PE COFF offset

    (4 bytes, offset 0x3C)

    40 00 00 00

Our NuttX Kernel shall recreate this RISC-V Linux Image Header. (Total 0x40 bytes)

(Or U-Boot Bootloader might refuse to boot NuttX)

Header Values are exactly the same as Star64. (Except the Image Size and Executable Code, since the Jump Address is different)

TODO