Random gibberish on TPLink EX220 UART

Hi,

I'm trying to get into the UART of the EX220 on baud 115200 8 databits 1 stopbit no parity no flow control but I just get some random gibberish spam.

I connected my serial cable through a level shifter. Without the level shifter it had the same result.

Does anyone have any ideas on what is going wrong?

Console output:

Board:

Underside:

Wrong baudrate, you connected RX/TX the wrong way around, you didn't connect GND....

I tried every baud rate, I did connect ground. The router refuses to boot if RX/TX are switched

What level shifter?

You are supposed to use a TTL serial cable.

I used a USB - RS232 cable and connected the TX, RX and GND pins.

I measured the RS232 cable to have a voltage of 6V so I used a level shifter to get it down to 3.3v

RS232 is not the same thing. RS232 uses both positive and negative voltages for communications, TTL-level UART doesn't use negative voltages. RS232 also uses inverted levels for 1 and 0 compared to TTL UART. By using RS232 on the pins, you may have already fried your SoC.

https://www.sparkfun.com/tutorials/215

3 Likes

That is not possible to measure like that since rs232 is differential voltage signals so that signal is free floating from ground and 15V between + and - cable.

Oh derp, I had RS232 cables because I manage a lot of enterprise switches/routers. Ordered a TTL cable. I'll update this thread in a couple of days when it arrived.

Thank you for the quick responses.

Been there done that😂

But my poor old wrt3200acm did survive😁

It was indeed just the cable.

I should probably open a new thread for this but I'm unable to have the router boot to OpenWRT

=> tftp openwrt.bin
Using eth@1e100000 device
TFTP from server 192.168.0.100; our IP address is 192.168.0.1
Filename 'openwrt.bin'.
Load address: 0x80010000
Loading: T #################################################################
  #################################################################
  #################################################################
  #################################################################
  #################################################################
  #################################################################
  #################################################################
  #################################################################
  #################################################################
  #################################################################
  #################################################################
  #################################################################
  #################################################################
  #################################################################
  #################################################################
  #
  285.2 KiB/s
done
Bytes transferred = 4993135 (4c306f hex)
=> bootm 0x80010000
## Booting kernel from Legacy Image at 80010000 ...
   Image Name:   MIPS OpenWrt Linux-5.4.188
   Image Type:   MIPS Linux Kernel Image (lzma compressed)
   Data Size:    4993071 Bytes = 4.8 MiB
   Load Address: 80001000
   Entry Point:  80001000
   Verifying Checksum ... OK
   Uncompressing Kernel Image ... lzma compressed: uncompress error 1
Must RESET board to recover

which image did you use, AFAIK it's not a supported device, or was it DIY ?

It's not listed as supported device, they are rather new. They also only ship to service providers as they have built-in remote management tools.

I see.

The LZMA error is pretty common, you can find several threads about it on the forum.

What compression was selected for kernel?

It actually looks like it's already running OpenWRT from the factory?

## Loading kernel from FIT Image at 80010000 ...
   Using 'config@1' configuration
   Trying 'kernel@1' kernel subimage
     Description:  MIPS OpenWrt Linux-4.4.198
     Type:         Kernel Image
     Compression:  lzma compressed
     Data Start:   0x800100e4
     Data Size:    3991654 Bytes = 3.8 MiB
     Architecture: MIPS
     OS:           Linux
     Load Address: 0x81001000
     Entry Point:  0x81001000
     Hash algo:    crc32
     Hash value:   0839e10e
     Hash algo:    sha1
     Hash value:   a344580f8713e7a72a272b8c58323d442f61a3b4
   Verifying Hash Integrity ... crc32+ sha1+ OK
## Loading fdt from FIT Image at 80010000 ...
   Using 'config@1' configuration
   Trying 'fdt@1' fdt subimage
     Description:  MIPS OpenWrt EX221-G5V1 device tree blob
     Type:         Flat Device Tree
     Compression:  uncompressed
     Data Start:   0x803dea88
     Data Size:    10998 Bytes = 10.7 KiB
     Architecture: MIPS
     Hash algo:    crc32
     Hash value:   56e738e1
     Hash algo:    sha1

Probably just customized openwrt with their own firmware? Or is this just from me trying to get openwrt to run. It is booting tplink's firmware here.

They all are, or LEDE.

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