I found the kernel boot parameters, and at least I saw something - kernel panic:
Found /extlinux/extlinux.conf
Retrieving file: /extlinux/extlinux.conf
197 bytes read in 15 ms (12.7 KiB/s)
1: Multitool
Retrieving file: /kernel.img
8719272 bytes read in 766 ms (10.9 MiB/s)
append: boot=UUID=C2A8-5A61 root=/dev/mmcblk0p2 console=uart8250,mmio32,0x11030000 console=uart0 verbose=1 consoleblank=0 video=HDMI-A-1
Retrieving file: /rk322x-box.dtb
46636 bytes read in 16 ms (2.8 MiB/s)
## Flattened Device Tree blob at 61f00000
Booting using the fdt blob at 0x61f00000
Loading Device Tree to 683f1000, end 683ff62b ... OK
Starting kernel ...
[ 0.000000] Booting Linux on physical CPU 0xf00
[ 0.000000] Initializing cgroup subsys cpuset
[ 0.000000] Initializing cgroup subsys cpu
[ 0.000000] Initializing cgroup subsys cpuacct
[ 0.000000] Linux version 4.4.194-rk322x (root@armbianbuild) (gcc version 8.3.0 (GNU Toolchain for the A-profile Architecture 8.3-2019.03 (arm-rel-8.36)) ) #47 SMP Thu Apr 9 17:37:46 UTC 2020
[ 0.000000] CPU: ARMv7 Processor [410fc075] revision 5 (ARMv7), cr=10c5387d
[ 0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing instruction cache
[ 0.000000] Machine model: Generic RK322x TV Box board
[ 0.000000] earlycon: Early serial console at MMIO32 0x11030000 (options '')
[ 0.000000] bootconsole [uart0] enabled
[ 0.000000] cma: Reserved 128 MiB at 0x98000000
[ 0.000000] Memory policy: Data cache writealloc
[ 0.000000] psci: probing for conduit method from DT.
[ 0.000000] psci: PSCIv65535.65535 detected in firmware.
[ 0.000000] psci: Using standard PSCI v0.2 function IDs
[ 0.000000] psci: MIGRATE_INFO_TYPE not supported.
[ 0.000000] PERCPU: Embedded 14 pages/cpu @e7659000 s24856 r8192 d24296 u57344
[ 0.000000] Built 1 zonelists in Zone order, mobility grouping on. Total pages: 256256
[ 0.000000] Kernel command line: boot=UUID=C2A8-5A61 root=/dev/mmcblk0p2 console=uart8250,mmio32,0x11030000 console=uart0 verbose=1 consoleblank=0 video=HDMI-A-1
[ 0.000000] PID hash table entries: 4096 (order: 2, 16384 bytes)
[ 0.000000] Dentry cache hash table entries: 131072 (order: 7, 524288 bytes)
[ 0.000000] Inode-cache hash table entries: 65536 (order: 6, 262144 bytes)
[ 0.000000] Memory: 871700K/1034240K available (12820K kernel code, 875K rwdata, 3224K rodata, 796K init, 1219K bss, 31468K reserved, 131072K cma-reserved, 0K highmem)
[ 0.000000] Virtual kernel memory layout:
[ 0.000000] vector : 0xffff0000 - 0xffff1000 ( 4 kB)
[ 0.000000] fixmap : 0xffc00000 - 0xfff00000 (3072 kB)
[ 0.000000] vmalloc : 0xf0800000 - 0xff800000 ( 240 MB)
[ 0.000000] lowmem : 0xb0000000 - 0xf0000000 (1024 MB)
[ 0.000000] pkmap : 0xafe00000 - 0xb0000000 ( 2 MB)
[ 0.000000] modules : 0xaf000000 - 0xafe00000 ( 14 MB)
[ 0.000000] .text : 0xb0008000 - 0xb0c8d53c (12822 kB)
[ 0.000000] .init : 0xb10a1000 - 0xb1168000 ( 796 kB)
[ 0.000000] .data : 0xb1168000 - 0xb1242e94 ( 876 kB)
[ 0.000000] .bss : 0xb1244000 - 0xb1374ee4 (1220 kB)
[ 0.000000] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=4, Nodes=1
[ 0.000000] Hierarchical RCU implementation.
[ 0.000000] Build-time adjustment of leaf fanout to 32.
[ 0.000000] NR_IRQS:16 nr_irqs:16 16
[ 0.000000] Architected cp15 timer(s) running at 24.00MHz (phys).
[ 0.000000] clocksource: arch_sys_counter: mask: 0xffffffffffffff max_cycles: 0x588fe9dc0, max_idle_ns: 440795202592 ns
[ 0.000008] sched_clock: 56 bits at 24MHz, resolution 41ns, wraps every 4398046511097ns
[ 0.008796] Switching to timer-based delay loop, resolution 41ns
[ 0.017166] Console: colour dummy device 80x30
[ 0.022089] Unable to handle kernel NULL pointer dereference at virtual address 00000000
[ 0.030986] pgd = b0004000
[ 0.033954] [00000000] *pgd=00000000
[ 0.037902] Internal error: Oops: 5 [#1] SMP ARM
[ 0.042967] Modules linked in:
[ 0.046107] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.4.194-rk322x #47
[ 0.053458] Hardware name: Generic DT based system
[ 0.058713] task: b1174538 task.stack: b1168000
[ 0.063286] PC is at strncmp+0x1c/0x70
[ 0.067095] LR is at 0x6d
[ 0.069969] pc : [<b0536e90>] lr : [<0000006d>] psr: 20000053
[ 0.069969] sp : b1169ed8 ip : 00000000 fp : b1169ee4
[ 0.082072] r10: b05e9528 r9 : 00000001 r8 : b117bfe0
[ 0.087804] r7 : b1169f13 r6 : b1169f14 r5 : b1169f0c r4 : 00000000
[ 0.094966] r3 : b1169f0c r2 : 00000005 r1 : b0ec5add r0 : 00000000
[ 0.102121] Flags: nzCv IRQs on FIQs off Mode SVC_32 ISA ARM Segment none
[ 0.109369] Control: 10c5387d Table: 6000406a DAC: 00000051
[ 0.115135] Process swapper/0 (pid: 0, stack limit = 0xb1168250)
[ 0.121725] Stack: (0xb1169ed8 to 0xb116a000)
[ 0.126151] 9ec0: b1169f04 b1169ee8
[ 0.134350] 9ee0: b05e5eb4 b0536e80 b11e0ebc b1246cac b11e0d60 b1246848 b1169f3c b1169f08
[ 0.143330] 9f00: b05e9590 b05e5e8c 00000400 00000000 0308d398 11030000 75000001 00747261
[ 0.151563] 9f20: b1169f44 b11e0ebc b1246cac b11e0d60 b1169f74 b1169f40 b008d7a4 b05e9534
[ 0.159814] 9f40: b1350c40 b10d768c 00000004 b11e0eb4 b1160ad8 b11130e8 b1244000 e7fffc80
[ 0.168065] 9f60: b0f206e0 b116e540 b1169f8c b1169f78 b10d76c0 b008d6b4 b1160ad8 b1160ad8
[ 0.176307] 9f80: b1169fa4 b1169f90 b10d6778 b10d76a0 ffffffff 00000000 b1169ff4 b1169fa8
[ 0.184557] 9fa0: b10a1c94 b10d6754 ffffffff ffffffff 00000000 b10a15fc 00000000 b1114250
[ 0.192765] 9fc0: 00000000 b1114250 00000000 b1244294 b116e5c0 b111424c b1175b44 6000406a
[ 0.201007] 9fe0: 410fc075 00000000 00000000 b1169ff8 6000807c b10a197c 00000000 00000000
[ 0.209254] [<b0536e90>] (strncmp) from [<b05e5eb4>] (uart_parse_earlycon+0x34/0x14c)
[ 0.217126] [<b05e5eb4>] (uart_parse_earlycon) from [<b05e9590>] (univ8250_console_match+0x68/0x118)
[ 0.227161] [<b05e9590>] (univ8250_console_match) from [<b008d7a4>] (register_console+0xfc/0x3b8)
[ 0.236088] [<b008d7a4>] (register_console) from [<b10d76c0>] (univ8250_console_init+0x2c/0x3c)
[ 0.244810] [<b10d76c0>] (univ8250_console_init) from [<b10d6778>] (console_init+0x30/0x34)
[ 0.253232] [<b10d6778>] (console_init) from [<b10a1c94>] (start_kernel+0x324/0x438)
[ 0.261018] [<b10a1c94>] (start_kernel) from [<6000807c>] (0x6000807c)
[ 0.267615] Code: e3520000 0a000010 e1a0c000 e4d1e001 (e4dc3001)
[ 0.273814] ---[ end trace cb88537fdc8fa200 ]---
[ 0.278902] Kernel panic - not syncing: Attempted to kill the idle task!
[ 0.285650] CRU:
[ 0.287678] 00000000: 00002044 00001441 00000000 0000304b 00001441 00000001 0000307d 00001442
[ 0.296287] 00000020: 00000001 00001032 00001441 00000000 00000000 00000000 00000000 00000000
[ 0.304887] 00000040: 00001111 00002700 00001013 00004203 0000001f 00000003 00000309 0000021f
[ 0.314250] 00000060: 0bb8ea60 0bb8ea60 0000001f 00001407 0000210b 00001d17 0000021f 0000021f
[ 0.322832] 00000080: 0000021f 0000001f 0bb8ea60 0bb8ea60 0bb8ea60 0bb8ea60 0000c2dc 00000f01
[ 0.332194] 000000a0: 0000412f 000003c3 0000011f 00000000 00000100 00004141 00000000 0bb8ea60
[ 0.340820] 000000c0: 00002121 00000021 00002122 00002121 00000000 00000000 00000000 00000000
[ 0.350182] 000000e0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[ 0.358781] 00000100: 00000000 00000000 00000000 00000000 000000e0 00000000 00000000 00000000
[ 0.367346] 00000120: 00000000 00000000 00000000 00000000 00000000 0000a000 00000000 00000000
[ 0.375919] 00000140: 3a980064 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[ 0.385281] 00000160: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[ 0.394634] 00000180: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[ 0.403181] 000001a0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[ 0.412542] 000001c0: 00000004 00000000 00000004 00000000 00000000 00000000 00000004 00000000
[ 0.421902] 000001e0: 00000000 00000000 00000000 00000000 00000000 00000000
[ 0.428911] ---[ end Kernel panic - not syncing: Attempted to kill the idle task!
does anyone know what he needs?