Apache NuttX RTOS for Pine64 Star64 64-bit RISC-V SBC (StarFive JH7110)

Read the articles...

• "64-bit RISC-V with Apache NuttX Real-Time Operating System"

• "Rolling to RISC-V"

Let's port Apache NuttX RTOS to Pine64 Star64 64-bit RISC-V SBC!

(Based on StarFive JH7110 SoC)

Hopefully NuttX will run on Pine64 PineTab-V, which is also based on StarFive JH7110 SoC.

Linux Images for Star64

Let's examine the Linux Images for Star64 SBC, to see how U-Boot Bootloader is configured. (We'll boot NuttX later with U-Boot)

According to Software Releases for Star64, we have...

• Yocto Images at pine64.my-ho.st

  Let's inspect star64-image-minimal

• Armbian Images

  Let's inspect Armbian 23.8 Lunar (Minimal)

Armbian Image for Star64

Let's inspect the Armbian Image for Star64: Armbian 23.8 Lunar (Minimal)

Uncompress the .xz, mount the .img file on Linux / macOS / Windows as an ISO Volume.

The image contains 1 used partition: armbi_root (642 MB) that contains the Linux Root Filesystem.

We see the U-Boot Bootloader Configuration at armbi_root/boot/uEnv.txt...

fdt_high=0xffffffffffffffff
initrd_high=0xffffffffffffffff

kernel_addr_r=0x44000000
kernel_comp_addr_r=0x90000000
kernel_comp_size=0x10000000

fdt_addr_r=0x48000000
ramdisk_addr_r=0x48100000

# Move distro to first boot to speed up booting
boot_targets=distro mmc1 dhcp 

distro_bootpart=1

# Fix missing bootcmd
bootcmd=run bootcmd_distro

kernel_addr_r says that Linux Kernel will be loaded at 0x4400 0000...

kernel_addr_r=0x44000000

(Yocto Image loads Linux Kernel at a different address, see next section)

This probably means that U-Boot Bootloader is loaded at 0x4000 0000.

U-Boot Bootloader loads the Linux Kernel from armbi_root/boot/Image

Which is sym-linked to armbi_root/boot/vmlinuz-5.15.0-starfive2

Here are the files in armbi_root/boot...

→ ls -l /Volumes/armbi_root/boot
total 94416
lrwxrwxrwx  1 Luppy  staff        24 Jun 21 13:59 Image -> vmlinuz-5.15.0-starfive2
-rw-r--r--  1 Luppy  staff   4276712 Jun 21 12:16 System.map-5.15.0-starfive2
-rw-r--r--  1 Luppy  staff      1536 Jun 21 14:00 armbian_first_run.txt.template
-rw-r--r--  1 Luppy  staff     38518 Jun 21 14:00 boot.bmp
-rw-r--r--  1 Luppy  staff    144938 Jun 21 12:16 config-5.15.0-starfive2
lrwxrwxrwx  1 Luppy  staff        20 Jun 21 13:59 dtb -> dtb-5.15.0-starfive2
drwxr-xr-x  1 Luppy  staff         0 Jun 21 13:59 dtb-5.15.0-starfive2
drwxrwxr-x  1 Luppy  staff         0 Jun 21 13:58 extlinux
lrwxrwxrwx  1 Luppy  staff        27 Jun 21 13:59 initrd.img -> initrd.img-5.15.0-starfive2
-rw-r--r--  1 Luppy  staff  10911474 Jun 21 14:01 initrd.img-5.15.0-starfive2
lrwxrwxrwx  1 Luppy  staff        27 Jun 21 13:59 initrd.img.old -> initrd.img-5.15.0-starfive2
-rw-rw-r--  1 Luppy  staff       341 Jun 21 14:00 uEnv.txt
lrwxrwxrwx  1 Luppy  staff        24 Jun 21 14:01 uInitrd -> uInitrd-5.15.0-starfive2
-rw-r--r--  1 Luppy  staff  10911538 Jun 21 14:01 uInitrd-5.15.0-starfive2
lrwxrwxrwx  1 Luppy  staff        24 Jun 21 13:59 vmlinuz -> vmlinuz-5.15.0-starfive2
-rw-r--r--  1 Luppy  staff  22040576 Jun 21 12:16 vmlinuz-5.15.0-starfive2
lrwxrwxrwx  1 Luppy  staff        24 Jun 21 13:59 vmlinuz.old -> vmlinuz-5.15.0-starfive2

Yocto Image for Star64

Let's inspect the Yocto Image for Star64: star64-image-minimal

Uncompress the .bz2, rename as .img. Balena Etcher won't work with .bz2 files!

Write the .img to a microSD Card with Balena Etcher. Insert the microSD Card into a Linux Machine. (Like Pinebook Pro)

We see 4 used partitions...

• spl (2 MB): Secondary Program Loader

• uboot (4 MB): U-Boot Bootloader

• boot (380 MB): Boot Configuration for U-Boot

• root (686 MB): Linux Root Filesystem

Plus 2 unused partitions. (Why?)

boot partition has 2 files...

$ ls -l /run/media/luppy/boot
total 14808
-rw-r--r-- 1 luppy luppy 15151064 Apr  6  2011 fitImage
-rw-r--r-- 1 luppy luppy     1562 Apr  6  2011 vf2_uEnv.txt

boot/vf2_uEnv.txt contains the U-Boot Bootloader Configuration...

# This is the sample jh7110_uEnv.txt file for starfive visionfive U-boot
# The current convention (SUBJECT TO CHANGE) is that this file
# will be loaded from the third partition on the
# MMC card.
#devnum=1
partnum=3

# The FIT file to boot from
fitfile=fitImage

# for debugging boot
bootargs_ext=if test ${devnum} = 0; then setenv bootargs "earlyprintk console=tty1 console=ttyS0,115200 rootwait earlycon=sbi root=/dev/mmcblk0p4"; else setenv bootargs "earlyprintk console=tty1 console=ttyS0,115200 rootwait earlycon=sbi root=/dev/mmcblk1p4"; fi;
#bootargs=earlyprintk console=ttyS0,115200 debug rootwait earlycon=sbi root=/dev/mmcblk1p4

# for addr info
fileaddr=0xa0000000
fdtaddr=0x46000000
# boot Linux flat or compressed 'Image' stored at 'kernel_addr_r'
kernel_addr_r=0x40200000
irdaddr=46100000
irdsize=5f00000

# Use the FDT in the FIT image..
setupfdt1=fdt addr ${fdtaddr}; fdt resize;

setupird=setexpr irdend ${irdaddr} + ${irdsize}; fdt set /chosen linux,initrd-start <0x0 0x${irdaddr}>; fdt set /chosen linux,initrd-end <0x0 0x${irdend}>

setupfdt2=fdt set /chosen bootargs "${bootargs}";

bootwait=setenv _delay ${bootdelay}; echo ${_delay}; while test ${_delay} > 0; do sleep 1; setexpr _delay ${_delay} - 1; echo ${_delay}; done

boot2=run bootargs_ext; mmc dev ${devnum}; fatload mmc ${devnum}:${partnum} ${fileaddr} ${fitfile}; bootm start ${fileaddr}; run setupfdt1;run setupird;run setupfdt2; bootm loados ${fileaddr}; run chipa_set_linux; run cpu_vol_set; echo "Booting kernel in"; booti ${kernel_addr_r} ${irdaddr}:${filesize} ${fdtaddr}

kernel_addr_r says that Linux Kernel will be loaded at 0x4020 0000...

# boot Linux flat or compressed 'Image' stored at 'kernel_addr_r'
kernel_addr_r=0x40200000

(Different from Armbian: 0x4400 0000)

So Yocto boots from the Flat Image Tree (FIT): boot/fitImage

Yocto's root/boot looks different from Armbian...

$ ls -l /run/media/luppy/root/boot
total 24376
lrwxrwxrwx 1 root root       17 Mar  9  2018 fitImage -> fitImage-5.15.107
-rw-r--r-- 1 root root  9807808 Mar  9  2018 fitImage-5.15.107
-rw-r--r-- 1 root root 15151064 Mar  9  2018 fitImage-initramfs-5.15.107

Boot NuttX with U-Boot Bootloader

Will we boot NuttX with Armbian or Yocto settings? 0x4400 0000 or 0x4020 0000?

Armbian looks simpler, since it uses a plain Linux Kernel Image File Image. (Instead of Yocto's complicated Flat Image Tree)

Hence we will overwrite Armbian's armbi_root/boot/Image by the NuttX Kernel Image.

Inside the Armbian Kernel Image

What's inside the Armbian Linux Kernel Image?

Let's look inside armbi_root/boot/Image...

See the "RISCV" at 0x30? That's the Magic Number for the RISC-V Linux Image Header!

• "Boot image header in RISC-V Linux"

u32 code0;                /* Executable code */
u32 code1;                /* Executable code */
u64 text_offset;          /* Image load offset, little endian */
u64 image_size;           /* Effective Image size, little endian */
u64 flags;                /* kernel flags, little endian */
u32 version;              /* Version of this header */
u32 res1 = 0;             /* Reserved */
u64 res2 = 0;             /* Reserved */
u64 magic = 0x5643534952; /* Magic number, little endian, "RISCV" */
u32 magic2 = 0x05435352;  /* Magic number 2, little endian, "RSC\x05" */
u32 res3;                 /* Reserved for PE COFF offset */

Let's analyse the Armbian Linux Kernel Image with Ghidra...

• Language: RISCV > RV64GC (RISCV:LE:64:RV64GC:gcc)

  (StarFive JH7110 has 4 × RV64GC U74 Application Cores)

TODO