You were right: setting putty to 115200 speed fixed the issue!
Nanopi-k2 u-boot gave me a nice boot sequence and shell; i don't know what command you need, hope this helps
$this->bbcode_second_pass_code('', 'GXBB:BL1:08dafd:0a8993;FEAT:EDFC318C;POC:3;RCY:0;EMMC:800;NAND:81;SD:0;READ:0;CHK:0;
no sdio debug board detected
TE: 224894
BL2 Built : 12:06:06, Jun 13 2016.
gxb g176ecdb - laiyin.mo@droid12-sz
set vcck to 1100 mv
set vddee to 1000 mv
Board ID = 8
CPU clk: 1536MHz
DDR chl: Rank0+1 same @ 792MHz
DDR0: 2048MB(auto)-2T-11
DataBus test pass!
AddrBus test pass!
Load fip header from SD, src: 0x0000c200, des: 0x01400000, size: 0x00004000
New fip structure!
Load bl30 from SD, src: 0x00010200, des: 0x01000000, size: 0x0000d460
Sending bl30......................................................OK.
Run bl30...
Load bl31 from SD, src: 0x00020200, des: 0x101000[0, size: 0x00013140
Image: gxb_v1.1.3134-b387442 2016-06-16 14:48:44 yun.cai@droid06]
OPS=0x13
67 89 db 86 3d d9 aa 71 4c d6 8b fe [0.322092 Inits done]
secure task start!
high task start!
low task start!
Load bl33 from SD, src: 0x00034200, des: 0x01000000, size: 0x0006ae70
NOTICE: BL3-1: v1.0(debug):c813a61
NOTICE: BL3-1: Built : 14:47:05, Jun 16 2016
INFO: BL3-1: Initializing runtime services
WARNING: No OPTEE provided by BL2 boot loader
ERROR: Error initializing runtime service opteed_fast
INFO: BL3-1: Preparing for EL3 exit to normal world
INFO: BL3-1: Next image address = 0x1000000
INFO: BL3-1: Next image spsr = 0x3c9
U-Boot 2015.01-00014-g4ef665ff6c (Sep 04 2017 - 09:45:00)
DRAM: 2 GiB
Relocation Offset is: 76f3b000
register usb cfg[1][0] = 0000000077f96a30
register usb cfg[0][1] = 0000000077f96a50
register usb cfg[2][0] = 0000000077f96a70
vpu: error: vpu: check dts: FDT_ERR_BADMAGIC, load default parameters
vpu: clk_level = 7
vpu: set clk: 666667000Hz, readback: 666660000Hz(0x300)
MMC: SDIO Port B: 0, SDIO Port C: 1
[mmc_init] mmc init success
In: serial
Out: serial
Err: serial
reboot_mode=cold_boot
hpd_state=0
cvbs performance type = 4, table = 0
Net: Meson_Ethernet
** File not found nanopi-k2.dtb **
libfdt fdt_check_header(): FDT_ERR_BADMAGIC
[OSD]check dts: FDT_ERR_BADMAGIC, load default fb_addr parameters
[OSD]fb_addr for logo: 0x3d800000
[OSD]check dts: FDT_ERR_BADMAGIC, load default fb_addr parameters
[OSD]fb_addr for logo: 0x3d800000
[CANVAS]addr=0x3d800000 width=5760, height=2160
270054 bytes read in 25 ms (10.3 MiB/s)
Hit Enter or space or Ctrl+C key to stop autoboot -- : 0
** File not found Image **
** File not found ramdisk.img **
Bad Linux ARM64 Image magic!
nanopi-k2#
nanopi-k2#printenv
baudrate=115200
bloader=ext4load mmc 0:1
bootargs=console=ttyS0,115200 no_console_suspend earlyprintk=aml-uart,0xc81004c0 androidboot.console=ttyS0 androidboot.hardware=nanopi-k2 hdmimode=1080p60hz hdmitx=cecf logo=osd1,loaded,0x3d800000,1080p60hz initrd=0x39000000,0x
bootcmd=run loadkernel; run loadinitrd; run init_bootargs; booti ${loadaddr} - ${dtb_mem_addr}
bootdelay=3
consoleargs=console=ttyS0,115200 no_console_suspend earlyprintk=aml-uart,0xc81004c0
cvbs_drv=0
cvbsmode=576cvbs
display_bpp=24
display_color_bg=0
display_color_fg=0xffff
display_color_index=24
display_height=576
display_layer=osd0
display_width=720
droidargs=androidboot.console=ttyS0 androidboot.hardware=nanopi-k2
dtb_mem_addr=0x1000000
dtb_name=nanopi-k2.dtb
ethact=Meson_Ethernet
ethaddr=00:16:0F:A0:10:22
fb_addr=0x3d800000
fb_height=1080
fb_width=1920
fdt_high=0x20000000
firstboot=1
gatewayip=192.168.102.1
hdmimode=1080p60hz
hostname=nanopi-k2-u1
init_bootargs=setenv bootargs ${consoleargs} ${droidargs} hdmimode=${hdmimode} hdmitx=cecf logo=osd1,loaded,${fb_addr},${hdmimode} initrd=${initrd_start},${initrd_size}
init_display=osd open; osd clear; ${bloader} 0x20000000 logo.bmp; bmp display 0x20000000
initrd_high=0x40000000
initrd_name=ramdisk.img
initrd_size=0x
initrd_start=0x39000000
ipaddr=192.168.102.39
loadaddr=0x1080000
loadbootimg=${bloader} 0x20000000 boot.img
loaddtb=${bloader} ${dtb_mem_addr} ${dtb_name}; fdt addr ${dtb_mem_addr}
loadinitrd=${bloader} ${initrd_start} ${initrd_name}; setenv initrd_size 0x${filesize}
loadkernel=${bloader} ${loadaddr} Image
netmask=255.255.255.0
outputmode=576cvbs
preboot=run loaddtb; run init_display
reboot_mode=cold_boot
serial#=fe2017a905b20003
serverip=192.168.102.30
stderr=serial
stdin=serial
stdout=serial
upgrade_step=0
Environment size: 1866/65532 bytes
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PS: nanopi-k2's HDMI is giving me hell, it only sets at 1080p cropping on lower resolution and detaching the cable after boot will give you a permanent black scren; i need it for a multimedia project so it's basicalli useless as it is!