NuttX boots a tiny bit on Ox64 yay! See https://lupyuen.github.io/articles/ox64

ox64-nuttx2.log

[I][] 
[I][]   ____                   ____               __  __      _       
[I][]  / __ \                 |  _ \            / _|/ _|    | |      
[I][] | |  | |_ __   ___ _ __ | |_) | ___  _   _| |_| |_ __ _| | ___  
[I][] | |  | | '_ \ / _ \ '_ \|  _ < / _ \| | | |  _|  _/ _` | |/ _ \ 
[I][] | |__| | |_) |  __/ | | | |_) | (_) | |_| | | | || (_| | | (_) |
[I][]  \____/| .__/ \___|_| |_|____/ \___/ \__,_|_| |_| \__,_|_|\___/ 
[I][]        | |                                                      
[I][]        |_|                                                      
[I][] 
[I][] Powered by BouffaloLab
[I][] Build:11:52:04,Mar  6 2023
[I][] Copyright (c) 2023 OpenBouffalo team
[I][] Copyright (c) 2022 Bouffalolab team
[I][] dynamic memory init success,heap s[I][LowLoad] D0 start...
[I][LowLoad] low_load start... 
[I][LowLoad] Header at 0x5d5ff000
[I][LowLoad] Section dtb(1) - Start 0x5d5ff100, Size 14314
[I][LowLoad] Copying DTB to 0x51ff8000...0x51ffb7ea
[I][LowLoad] Done!
[I][LowLoad] Section OpenSBI(2) - Start 0x5d60f100, Size 109864
[I][LowLoad] Copying OpenSBI to 0x3ef80000...0x3ef9ad28
[I][LowLoad] Done!
[I][LowLoad] Section Kernel(3) - Start 0x5d62f100, Size 315597
[I][LowLoad] Uncompressing Kernel to 0x50000
[I][LowLoad] Done!
[I][LowLoad] CRC: 00000000
[I][LowLoad] load time: 61308 us 
[I][LowLoad] Setting PMP
[I][LowLoad] Booting OpenSBI at 0x000000003ef80000 with DTB at 0x51ff8000

OpenSBI v1.2
   ____                    _____ ____ _____
  / __ \                  / ____|  _ \_   _|
 | |  | |_ __   ___ _ __ | ___ | |_) || |
 | |  | | '_ \ / _ \ '_ \ \___ \|  _ < | |
 | |__| | |_) |  __/ | | |____) | |_) || |_
  \____/| .__/ \___|_| |_|_____/|____/_____|
        | |
        |_|

Platform Name             : Pine64 Ox64 (D0)
Platform Features         : medeleg
Platform HART Count       : 1
Platform IPI Device       : aclint-mswi
Platform Timer Device     : aclint-mtimer @ 1000000Hz
Platform Console Device   : bflb_uart
Platform HSM Device       : ---
Platform PMU Device       : ---
Platform Reboot Device    : ---
Platform Shutdown Device  : ---
Firmware Base             : 0x3ef80000
Firmware Size             : 200 KB
Runtime SBI Version       : 1.0

Domain0 Name              : root
Domain0 Boot HART         : 0
Domain0 HARTs             : 0*
Domain0 Region00          : 0x00000000e4008000-0x00000000e400bfff (I)
Domain0 Region01          : 0x00000000e4000000-0x00000000e4007fff (I)
Domain0 Region02          : 0x000000003ef80000-0x000000003efbffff ()
Domain0 Region03          : 0x0000000000000000-0xffffffffffffffff (R,W,X)
Domain0 Next Address      : 0x0000000050000000
Domain0 Next Arg1         : 0x0000000051ff8000
Domain0 Next Mode         : S-mode
Domain0 SysReset          : yes

Boot HART ID              : 0
Boot HART Domain          : root
Boot HART Priv Version    : v1.11
Boot HART Base ISA        : rv64imafdcvx
Boot HART ISA Extensions  : time
Boot HART PMP Count       : 8
Boot HART PMP Granularity : 4096
Boot HART PMP Address Bits: 38
Boot HART MHPM Count      : 8
Boot HART MIDELEG         : 0x0000000000000222
Boot HART MEDELEG         : 0x000000000000b109


U-Boot 2023.04-rc2 (Mar 06 2023 - 11:48:40 +0000)

DRAM:  64 MiB
Core:  36 devices, 17 uclasses, devicetree: board
MMC:   mmc@20060000: 0
Loading Environment from FAT... Unable to read "uboot.env" from mmc0:2... 
Loading Environment from nowhere... OK
In:    serial@30002000
Out:   serial@30002000
Err:   serial@30002000
Net:   
Warning: emac@20070000 (eth0) using random MAC address - c6:5a:43:ac:52:74
eth0: emac@20070000
Hit any key to stop autoboot:  0 
switch to partitions #0, OK
mmc0 is current device
Scanning mmc 0:2...
Found /extlinux/extlinux.conf
Retrieving file: /extlinux/extlinux.conf
Select the boot mode
1:.Pine64 0X64 Kernel
2:.Sipeed M1SDock Kernel
Enter choice: 1:.Pine64 0X64 Kernel
Retrieving file: /extlinux/../Image
append: root=PARTLABEL=rootfs rootwait rw rootfstype=ext4 console=ttyS0,2000000 loglevel=8 earlycon=sbi
Retrieving file: /extlinux/../bl808-pine64-ox64.dtb
## Flattened Device Tree blob at 51ff8000
   Booting using the fdt blob at 0x51ff8000
Working FDT set to 51ff8000
   Loading Device Tree to 0000000053f22000, end 0000000053f25fab ... OK
Working FDT set to 53f22000

Starting kernel ...

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