The tty0tty directory tree is divided in:

module - linux kernel module null-modem
pts - null-modem using ptys (without handshake lines)

When run connect two pseudo-ttys and show the connection names:

(/dev/pts/1) <=> (/dev/pts/2)

the connection is:

TX -> RX
RX <- TX

The module is tested in kernel 3.10.2 (debian)

When loaded, create 8 ttys interconnected:

/dev/tnt0 <=> /dev/tnt1
/dev/tnt2 <=> /dev/tnt3
/dev/tnt4 <=> /dev/tnt5
/dev/tnt6 <=> /dev/tnt7

the connection is:

TX -> RX
RX <- TX
RTS -> CTS
CTS <- RTS
DSR <- DTR
CD <- DTR
DTR -> DSR
DTR -> CD

For building the module kernel-headers or kernel source are necessary.

Download the tty0tty package from one of these sources: Clone the repo https://github.com/freemed/tty0tty

git clone https://github.com/freemed/tty0tty

Build the kernel module from provided source

cd tty0tty-1.2/module
make

Install the new kernel module into the kernel modules directory

sudo make modules_install

NOTE: if module signing is enabled, in order for depmop to complete, you may need to create file certs/x509.genkey in the kernel modules include directory and generate file signing_key.pem using openssl, guides are available online.

Appropriate permissions are provided thanks to a udev rule located under:

/etc/udev/rules.d/50-tty0tty.rules

NOTE: you need to add yourself to the dialout group (and do a full relog), with:

sudo usermod -a -G dialout ${USER}

Load the module

sudo udevadm control --reload-rules
sudo depmod
sudo modprobe tty0tty

You should see new serial ports in /dev/ (ls /dev/tnt*) You can now access the serial ports as /dev/tnt0 (1,2,3,4 etc) Note that the consecutive ports are interconnected. For example, /dev/tnt0 and /dev/tnt1 are connected as if using a direct cable.

Persisting across boot:

edit the file /etc/modules (Debian) or /etc/modules.conf

nano /etc/modules

and add the following line:

tty0tty

Note that this method will not make the module persist over kernel updates so if you ever update your kernel, make sure you build tty0tty again repeat the process.

In order to build the dkms Debian package

sudo apt-get update && sudo apt-get install -y dh-make dkms build-essential
debuild -uc -us

In order to integrate tty0tty into Yocto, please copy contents of 'yocto' folder add to your local.conf

IMAGE_INSTALL_append = " \
 tty0tty-module \
"

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