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I've been probing this CCTV DVR board trying to find a serial port to see if I can get console access to it. I found a set of 4 through holes with no headers that looked like a good candidate. I hooked up to my Bus Pirate in UART mode at a baud rate of 115200 and it seemed promising at first:

System startup

U-Boot 2010.06 (Dec 27 2018 - 17:06:41)

Check Flash Memory Controller v100 ... Found
SPI Nor(cs 0) ID: 0xc2 0x20 0x18
Block:64KB Chip:16MB Name:"MX25L128XX"
SPI Nor total size: 16MB
*** Warning - bad CRC, using default environment

In:    serial
Out:   serial
Err:   serial

Then things get weird. The next line has legible text but some garbage in it, then after that nothing but garbage:

�P���Starting the controller
+*/�)))!)       �!�+!%) !      �)*+��

%+���5�!                                -��5�!
        !�!
           +-���
                !���
�%      %!-     �)�����+��+     !       %!!5!!�)!+!
+)      %%�+
                %!5                                                                                                                                                                                          )
                   ��)5 !5)!)   %               �)!%
        -
         %)     )       5)�-�
!                               )��!�   !
 -      )!
%-
  !%!   !       !

!��
%)!�%   %%)!    !�      �
%!�))   !)!)!)!%-
�-))!   ��      ��)))!! ��%
�%!)�!)%)�))%              �)           %-%+�
�)      !�5�    !       �               !       -!!
            )%!
��)�)%�)���)

Is this because the baud rate is suddenly changing? Or is it more likely that the output is switching to some proprietary format?

I also didn't have a super solid connection to the board when trying this, could it be that the connection dropped and then reconnected out of sync or something?

  • Maybe the data is just sent in byte format rather than ASCII data? – morsisko May 26 at 18:15
  • It could be a flaky connection, although the signal-to-noise ratio seems a bit poor for that – multithr3at3d May 26 at 22:59
  • Most likely a proprietary format, but a change in encoding (ascii->unicode, etc) may cause this behaviour too. Try to reset the connection at this point. Also, try logging the data in binary format so you don't miss the non-printable characters and get more valuable information to research. – Yotamz May 27 at 6:32
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In my case it was a flaky connection. I was originally just using jumper wires to make contact into the through holes on the board and hook it up to the bus pirate. I soldered header pins to it and now I can see the output totally clearly.

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