How to Setup Serial Console Cable Over the Rock64 SBC

[MarkHaysHarris777]

Greetings,

  This photo blog shows how to setup a direct uart serial console connection using the uart(s) from another SBC like the PineA64+;  or any other SBC, like the Raspberry PI, or the Rock64.  This is a variation on a theme using our old friend the modified cat5 cable ( RJ45 plugs have been removed and replaced with standard header pins ).  The same cable carries two uart connections ( in this case one to Rock64-A and the other to Rock64-B ).  The host serial controller is, in this case, the PineA64+ desktop machine.

Preparation and Materials

Besides the remote machines ( the Rocks ) and the host controller ( the Pine ) you will also need one cat5 cable ( 1.8m works well ) and twelve(12) standard F-F 6" bread-board jumper wires to make the connections.  An adapter board is not necessary in this use case because the uart connections are direct;  Rx-->Tx,  Tx-->Rx,  gnd--gnd,  for each remote machine. 

              


In the picture(s) above you can see the details of the connections on the remote side of the comm link.  The cat5 cable has been opened and the RJ45 plugs have been replaced with header pins;  the orange pair was removed for hook-up wire.  I'm using the blue pair for ( Tx Rx ) on the Rock64-A, and the green pair for the ( Tx Rx ) on the Rock64-B.  The brown pair is being used for the ground returns;  all three wires are necessary for each machine uart direct connection.

At this juncture I'll point out that each pair has a solid and striped color for the pair ( blue brown or green ). For a given machine if the Tx of the remote is connected to the solid color, the Tx of the host for that connection must be connected to the striped wire.  This guarantees that Rx-->Tx, Tx-->Rx, gnd--gnd  is true for both machines.  Of course it is entirely arbitrary which way you do this, as long as you're logically (and color wise) consistent !

Modifying the cat5 cable is straight-forward and the easiest approach.  You might alternatively decide to use a juntion box of some sort containing header pins and RJ45 connectors;  this does not require modifying the cat5 cable but is more involved ( and more expensive ) in terms of time and money.

The pic above right shows the big picture;  again, I like to tape the transmission line to the table top and keep it out of the way, and its best to keep the jumper wires organized and neat.

         


In the enlarged inset detail above I am showing the host controller connections on the PineA64+ , utilizing the uart(3) and uart(4) , /dev/ttyS3  &  /dev/ttyS4 respectively.

The transmission cable ( modded cat5 ) comes into the pic on the top right-hand side.  I have labeled the wires as carefully as possible because it is hard to see how they terminate at the euler bus visually. Again, each uart connection is direct and each connection requires three wires; Rx-->Tx,  Tx-->Rx,  gnd--gnd.

I will be using the PineA64+ uart devices  /dev/ttyS3  &  /dev/ttyS4;  these devices live physically on the euler bus, the pinouts of which may be seen in this diagram.

Again, its important to note ( even repeat pedantically ) that the Tx and Rx lines of each connection MUST cross;  the easiest way to keep this straight is that if you connect Tx to solid blue on one end, connect Tx to striped blue on the other end !

Once the connections are made you can start the vt102 terminal emulation software in minicom;  for all intents and purposes this is the same here as in our previous adapter use case(s).

   important note:    If the transmit line from the host controller is connected to the Rock64 board at boot-up often the Rock64 will not boot.    The simple solution is to wait to plug in the Tx line from the host controller until after the Rock64 has booted and the logon prompt appears on the console.

Start the VT102 Terminal Emulation Software in Minicom

Open a terminal on the host controller ( PineA64+ in this case )  and drag the bottom of the window frame until the indicator shows  80 x 25.  This is important if you want to see the status bar on your minicom session!  Start the VT102 terminal emulation software with the following command:

       sudo   minicom  -s  -D  /dev/ttyS3  -b  1500000  --color=on

Note:  the baud rate is 1.5M  (1500000)  and the device is the uart(3);  Rock64-A in my case here.  

When the minicom opens and presents the config dialogue choose Serial Port Setup and press the enter key.  Make sure the defaults are correct, and also make sure that hardware & software flow control are off !  Press the enter key, and then select 'Exit' and press the enter key;  congratulations the VT102 terminal is running.  At this time ( if the remote machine is running ) you may press the enter key to get the logon prompt, and logon.  Otherwise, if the remote machine is NOT running, then apply power to the remote Rock64 and watch the boot-up messages scroll down the VT102 terminal.

               


Of course both of these connections ( Rock64-A  &  Rock64-B ) can be running at the same time;  to start the second connection open a tab on your terminal window and use the same command found above;  this time choosing the /dev/ttyS4 device ( everything else remains the same ).

In the left pic above you can see the Rock64-A connection running , and in the pic to the right you can see the Rock64-B connection running.  Both of these connections are running at 1.5 baud and without any adapters because the connections are direct uart-to-uart.

---

Notes:  

The host controller can be ANY SBC that you happen to have, another Rock64, a Raspberry PI, and Odroid, etc.  Also, the connection does not have to be dual;  a single connection works fine on the same modded cat5;  however, I will add this final caution :  the Rock64 uses a very fast connection speed ( for serial ) and 1.5M baud is subject to radio frequency impedance and transmission rules and mathematics;  due to reflections in the line, impedance mismatches may occur that will require you to perhaps modify the length of your transmission line;  although, in my setup a line length of about 1.8m works well.

Just for completeness, Rock64-A is my pre production board, and Rock64-B is my recent production test board.