tty0tty

linux null modem emulator v1.4

Directory tree

This is the tty0tty directory tree:

• module : linux kernel module null-modem
• pts : null-modem using ptys (without handshake lines)
• debian : debian package build tree
• ssniffer: simple serial sniffer using tty0tty driver ports

pts (unix98)

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

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

the connection is:

TX -> RX
RX <- TX

module

The module is tested in kernels from 3.10.2 to 5.3.15 (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

ssniffer

This is a simple serial sniffer program supporting handshake lines (using tty0tty module) with two working modes. In normal mode the data is displayed on the console as in the figure below. In ysplitter mode a third virtual port is connected and has access to the data sent by the device port and by the control application.

Precompiled .deb packages

You can get precompiled tty0tty dkms module or ssniffer packages from the piduino.org repository for Debian or Ubuntu :

wget -O- http://www.piduino.org/piduino-key.asc | sudo apt-key add -
sudo add-apt-repository 'deb http://apt.piduino.org buster piduino'
sudo apt update

The repository added in the add-apt-repository command is for the Debian Buster distribution, but you can also choose bullseye, bionic, focal or jammy.
These repositories provide packages for the amd64, armhf and arm64 architectures.

If the add-apt-repository command fails, install the software-properties-common package like this:

sudo apt install software-properties-common

module

sudo apt install tty0tty-dkms

ssniffer

sudo apt install ssniffer

Build from source

module

for module build is necessary kernel-headers or kernel source:

sudo apt-get  update
sudo apt-get  install linux-headers-`uname -r`
cd module
make
sudo make install

for debian package:

sudo apt-get install devscripts build-essential lintian debhelper

Download the archive file from https://github.com/lcgamboa/tty0tty/archive/refs/heads/master.zip

wget https://github.com/lcgamboa/tty0tty/archive/refs/heads/master.zip
unzip master.zip
cd tty0tty-master
dpkg-buildpackage

to clean:

dh_clean

make install set the devices permissions automatically in udev creating the file /etc/udev/rules.d/99-tty0tty.rules with rules:

SUBSYSTEM=="tty", KERNEL=="tnt0", GROUP="dialout", MODE="0660"
SUBSYSTEM=="tty", KERNEL=="tnt1", GROUP="dialout", MODE="0660"
SUBSYSTEM=="tty", KERNEL=="tnt2", GROUP="dialout", MODE="0660"
SUBSYSTEM=="tty", KERNEL=="tnt3", GROUP="dialout", MODE="0660"
SUBSYSTEM=="tty", KERNEL=="tnt4", GROUP="dialout", MODE="0660"
SUBSYSTEM=="tty", KERNEL=="tnt5", GROUP="dialout", MODE="0660"
SUBSYSTEM=="tty", KERNEL=="tnt6", GROUP="dialout", MODE="0660"
SUBSYSTEM=="tty", KERNEL=="tnt7", GROUP="dialout", MODE="0660"

It's possible edit rules and create permanent symbolic names with the parameter SYMLINK:

SUBSYSTEM=="tty", KERNEL=="tnt0", GROUP="dialout", MODE="0660", SYMLINK+="ttyUSB10"
SUBSYSTEM=="tty", KERNEL=="tnt1", GROUP="dialout", MODE="0660", SYMLINK+="ttyUSB11"

The user must be in the dialout group to access the ports. To add your user to dialout group use the command:

sudo usermod -a -G dialout your_user_name

after this is necessary logout and login to group permissions take effect.

To dkms support use the scripts dkms-install.sh and dkms-remove.sh

pts

cd pts
make

then run with:

./tty0tty

ssniffer

cd ssnifer
make
make install

for debian package:

dpkg-buildpackage

then for normal mode run with:

ssniffer /dev/ttyUSB0 2 color

and connect application in /dev/tnt3 virtual port.

Or for ysplitter mode run with:

ssniffer /dev/ttyUSB0 2 ysplitter4

and connect application in /dev/tnt3 virtual port and second terminal in /dev/tnt5 virtual port.

For e-mail suggestions : lcgamboa@yahoo.com