@KlenKlenov is talking about sxtG version, there are again two, one with 128 mb nand and new one with 16mb spi. They are not the same as sxt lite devices, the diference being in GB lan and lv4 licence on ros. They are unsupported and not working with openwrt.
Sxt lite old version with nand is fully supported, new version with spi flash works with forced upgrade. Here is a boot log...
[ 0.000000] Linux version 4.9.101 (buildbot@slashdirt-03) (gcc version 7.3.0 (OpenWrt GCC 7.3.0 r7021-a03035d) ) #0 Wed May 23 20:13:26 2018
[ 0.000000] bootconsole [early0] enabled
[ 0.000000] CPU0 revision is: 0001974c (MIPS 74Kc)
[ 0.000000] SoC: Atheros AR9344 rev 3
[ 0.000000] Determined physical RAM map:
[ 0.000000] memory: 04000000 @ 00000000 (usable)
[ 0.000000] User-defined physical RAM map:
[ 0.000000] memory: 04000000 @ 00000000 (usable)
[ 0.000000] Initrd not found or empty - disabling initrd
[ 0.000000] Primary instruction cache 64kB, VIPT, 4-way, linesize 32 bytes.
[ 0.000000] Primary data cache 32kB, 4-way, VIPT, cache aliases, linesize 32 bytes
[ 0.000000] Zone ranges:
[ 0.000000] Normal [mem 0x0000000000000000-0x0000000003ffffff]
[ 0.000000] Movable zone start for each node
[ 0.000000] Early memory node ranges
[ 0.000000] node 0: [mem 0x0000000000000000-0x0000000003ffffff]
[ 0.000000] Initmem setup node 0 [mem 0x0000000000000000-0x0000000003ffffff]
[ 0.000000] On node 0 totalpages: 16384
[ 0.000000] free_area_init_node: node 0, pgdat 804d9744, node_mem_map 81000020
[ 0.000000] Normal zone: 128 pages used for memmap
[ 0.000000] Normal zone: 0 pages reserved
[ 0.000000] Normal zone: 16384 pages, LIFO batch:3
[ 0.000000] pcpu-alloc: s0 r0 d32768 u32768 alloc=1*32768
[ 0.000000] pcpu-alloc: [0] 0
[ 0.000000] Built 1 zonelists in Zone order, mobility grouping on. Total pages: 16256
[ 0.000000] Kernel command line: no-uart no-nand parts=1 boot_part_size=16777216 gpio=261691 HZ=300000000 mem=64M kmac=6C:3B:6B:02:3E:8C board=911L board=911L ver=3.35 hw_opt=00204001 boot=1 mlc=10 console=ttyS0,115200 rootfstype=squashfs noinitrd
[ 0.000000] PID hash table entries: 256 (order: -2, 1024 bytes)
[ 0.000000] Dentry cache hash table entries: 8192 (order: 3, 32768 bytes)
[ 0.000000] Inode-cache hash table entries: 4096 (order: 2, 16384 bytes)
[ 0.000000] Writing ErrCtl register=00000000
[ 0.000000] Readback ErrCtl register=00000000
[ 0.000000] Memory: 59508K/65536K available (3581K kernel code, 158K rwdata, 844K rodata, 208K init, 217K bss, 6028K reserved, 0K cma-reserved)
[ 0.000000] SLUB: HWalign=32, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
[ 0.000000] NR_IRQS:51
[ 0.000000] Clocks: CPU:600.000MHz, DDR:450.000MHz, AHB:450.000MHz, Ref:25.000MHz
[ 0.000000] clocksource: MIPS: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 6370868154 ns
[ 0.000010] sched_clock: 32 bits at 300MHz, resolution 3ns, wraps every 7158278654ns
[ 0.008873] Calibrating delay loop... 299.82 BogoMIPS (lpj=1499136)
[ 0.081956] pid_max: default: 32768 minimum: 301
[ 0.087309] Mount-cache hash table entries: 1024 (order: 0, 4096 bytes)
[ 0.094824] Mountpoint-cache hash table entries: 1024 (order: 0, 4096 bytes)
[ 0.105780] clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 19112604462750000 ns
[ 0.116987] futex hash table entries: 256 (order: -1, 3072 bytes)
[ 0.125163] NET: Registered protocol family 16
[ 0.133431] MIPS: machine is MikroTik RouterBOARD SXT 2nD r3
[ 0.388522] clocksource: Switched to clocksource MIPS
[ 0.395433] NET: Registered protocol family 2
[ 0.401378] TCP established hash table entries: 1024 (order: 0, 4096 bytes)
[ 0.409350] TCP bind hash table entries: 1024 (order: 0, 4096 bytes)
[ 0.416569] TCP: Hash tables configured (established 1024 bind 1024)
[ 0.423881] UDP hash table entries: 256 (order: 0, 4096 bytes)
[ 0.430561] UDP-Lite hash table entries: 256 (order: 0, 4096 bytes)
[ 0.437949] NET: Registered protocol family 1
[ 0.442973] PCI: CLS 0 bytes, default 32
[ 0.446695] Crashlog allocated RAM at address 0x3f00000
[ 0.453666] workingset: timestamp_bits=30 max_order=14 bucket_order=0
[ 0.468489] squashfs: version 4.0 (2009/01/31) Phillip Lougher
[ 0.475153] jffs2: version 2.2 (NAND) (SUMMARY) (LZMA) (RTIME) (CMODE_PRIORITY) (c) 2001-2006 Red Hat, Inc.
[ 0.495395] io scheduler noop registered
[ 0.499902] io scheduler deadline registered (default)
[ 0.506179] Serial: 8250/16550 driver, 16 ports, IRQ sharing enabled
[ 0.516250] console [ttyS0] disabled
[ 0.540486] serial8250.0: ttyS0 at MMIO 0x18020000 (irq = 11, base_baud = 1562500) is a 16550A
[ 0.550287] console [ttyS0] enabled
[ 0.557832] bootconsole [early0] disabled
[ 0.572123] m25p80 spi0.0: found w25q128, expected m25p80
[ 0.589017] m25p80 spi0.0: w25q128 (16384 Kbytes)
[ 0.594293] Creating 6 MTD partitions on "spi0.0":
[ 0.599304] 0x000000000000-0x00000000e000 : "routerboot"
[ 0.606334] 0x00000000e000-0x00000000f000 : "hard_config"
[ 0.613656] 0x00000000f000-0x000000010000 : "bios"
[ 0.620359] 0x000000010000-0x00000001f000 : "routerboot2"
[ 0.627607] 0x00000001f000-0x000000020000 : "soft_config"
[ 0.634957] 0x000000020000-0x000001000000 : "firmware"
[ 0.642299] 2 minor-fw partitions found on MTD device firmware
[ 0.648342] 0x000000020000-0x0000001c0000 : "kernel"
[ 0.655264] 0x0000001c0000-0x000001000000 : "rootfs"
[ 0.662129] mtd: device 7 (rootfs) set to be root filesystem
[ 0.668005] 1 squashfs-split partitions found on MTD device rootfs
[ 0.674453] 0x0000003b0000-0x000001000000 : "rootfs_data"
[ 0.682765] libphy: Fixed MDIO Bus: probed
[ 0.699813] libphy: ag71xx_mdio: probed
[ 1.330277] ag71xx-mdio.1: Found an AR934X built-in switch
[ 1.382727] eth0: Atheros AG71xx at 0xba000000, irq 5, mode:GMII
[ 1.391234] NET: Registered protocol family 10
[ 1.399935] NET: Registered protocol family 17
[ 1.404586] bridge: filtering via arp/ip/ip6tables is no longer available by default. Update your scripts to load br_netfilter if you need this.
[ 1.418014] 8021q: 802.1Q VLAN Support v1.8
[ 1.429584] VFS: Mounted root (squashfs filesystem) readonly on device 31:7.
[ 1.438089] Freeing unused kernel memory: 208K
[ 1.442730] This architecture does not have kernel memory protection.
[ 2.012995] init: Console is alive
[ 2.016755] init: - watchdog -
[ 2.447232] random: fast init done
[ 2.817373] kmodloader: loading kernel modules from /etc/modules-boot.d/*
[ 2.872841] kmodloader: done loading kernel modules from /etc/modules-boot.d/*
[ 2.881381] init: - preinit -
[ 3.493772] IPv6: ADDRCONF(NETDEV_UP): eth0: link is not ready
[ 6.809755] jffs2: notice: (372) jffs2_build_xattr_subsystem: complete building xattr subsystem, 0 of xdatum (0 unchecked, 0 orphan) and 0 of xref (0 dead, 0 orphan) found.
[ 6.828799] mount_root: switching to jffs2 overlay
[ 6.861923] urandom-seed: Seeding with /etc/urandom.seed
[ 7.165606] procd: - early -
[ 7.168837] procd: - watchdog -
[ 7.803764] procd: - watchdog -
[ 7.807304] procd: - ubus -
[ 7.845615] random: ubusd: uninitialized urandom read (4 bytes read)
[ 7.862550] random: ubusd: uninitialized urandom read (4 bytes read)
[ 7.869715] random: ubusd: uninitialized urandom read (4 bytes read)
[ 7.877303] procd: - init -
[ 8.298364] kmodloader: loading kernel modules from /etc/modules.d/*
[ 8.313285] ip6_tables: (C) 2000-2006 Netfilter Core Team
[ 8.332559] Loading modules backported from Linux version wt-2017-11-01-0-gfe248fc2c180
[ 8.340883] Backport generated by backports.git v4.14-rc2-1-31-g86cf0e5d
[ 8.351278] ip_tables: (C) 2000-2006 Netfilter Core Team
[ 8.366532] nf_conntrack version 0.5.0 (1024 buckets, 4096 max)
[ 8.485586] wireguard: WireGuard 0.0.20180519 loaded. See www.wireguard.com for information.
[ 8.494362] wireguard: Copyright (C) 2015-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
[ 8.523307] xt_time: kernel timezone is -0000
[ 8.590851] PPP generic driver version 2.4.2
[ 8.597928] NET: Registered protocol family 24
[ 8.651455] ath: EEPROM regdomain: 0x0
[ 8.651465] ath: EEPROM indicates default country code should be used
[ 8.651468] ath: doing EEPROM country->regdmn map search
[ 8.651483] ath: country maps to regdmn code: 0x3a
[ 8.651489] ath: Country alpha2 being used: US
[ 8.651493] ath: Regpair used: 0x3a
[ 8.664557] ieee80211 phy0: Selected rate control algorithm 'minstrel_ht'
[ 8.668904] ieee80211 phy0: Atheros AR9340 Rev:3 mem=0xb8100000, irq=47
[ 8.784394] kmodloader: done loading kernel modules from /etc/modules.d/*
[ 9.735793] urandom_read: 5 callbacks suppressed
[ 9.735801] random: jshn: uninitialized urandom read (4 bytes read)
[ 9.759939] random: ubusd: uninitialized urandom read (4 bytes read)
[ 18.385061] br-lan: port 1(eth0) entered blocking state
[ 18.390523] br-lan: port 1(eth0) entered disabled state
[ 18.396296] device eth0 entered promiscuous mode
[ 18.459733] IPv6: ADDRCONF(NETDEV_UP): br-lan: link is not ready
[ 21.771859] IPv6: ADDRCONF(NETDEV_UP): wlan0-1: link is not ready
[ 21.782495] br-lan: port 2(wlan0-1) entered blocking state
[ 21.788174] br-lan: port 2(wlan0-1) entered disabled state
[ 21.794327] device wlan0-1 entered promiscuous mode
[ 22.863715] IPv6: ADDRCONF(NETDEV_UP): wlan0: link is not ready
[ 24.331272] wlan0: authenticate with 78:81:02:2a:d7:96
[ 24.354052] wlan0: send auth to 78:81:02:2a:d7:96 (try 1/3)
[ 24.363744] wlan0: authenticated
[ 24.368749] wlan0: associate with 78:81:02:2a:d7:96 (try 1/3)
[ 24.378147] wlan0: RX AssocResp from 78:81:02:2a:d7:96 (capab=0x411 status=0 aid=1)
[ 24.386363] wlan0: associated
[ 24.410453] IPv6: ADDRCONF(NETDEV_CHANGE): wlan0: link becomes ready
[ 25.051158] IPv6: ADDRCONF(NETDEV_CHANGE): wlan0-1: link becomes ready
[ 25.058110] br-lan: port 2(wlan0-1) entered blocking state
[ 25.063841] br-lan: port 2(wlan0-1) entered forwarding state
[ 25.077920] IPv6: ADDRCONF(NETDEV_CHANGE): br-lan: link becomes ready
[ 57.503380] random: crng init done
sxt lite 5 Ac is another diferent device, probably similar to lite 5 with diverent radio and board id. without board id nothing can be done to try and support it. The easyest way i know io get the board id is to get it from a supout file. If someone can send me supout taken on original firmware from this sxt i will get board id out of it.