How to use TTY with User Terminal




1 Purpose[edit]

This article describes how to use TTY with a user terminal. The TTY overview is described in Serial TTY overview article.

The use case of the following examples is a data transfer between a STM32 MPU board and PC, over a USB to a RS232 adapter cable.
The setup of this use case is described in details in the How to get Terminal article.


For the following examples:

  • uart4 is activated by default (for the Linux console)
  • usart3 is enabled by device tree
  • The usart3 pins are connected to a RS232 card
  • The RS232 card is connected to the PC over the USB to RS232 adapter cable.

Note: Some TTY tools are used in this article. A list of TTY tools is defined a dedicated article [TTY Tools ].

2 Print the file name of the terminal connected to standard input (with tty tool)[edit]

Board $> tty
# The console is connected to uart4 (aka ttySTM0) #
/dev/ttySTM0

3 Change serial port configuration (with stty tool)[edit]

Many serial port properties can be displayed and changed with the stty tool. The full feature list is available in stty user manual pages [1] .

Board $> stty --help
  • Display the current configuration:
Board $> stty -a -F /dev/ttySTM1
# Display the configuration of uart3 (aka ttySTM1) #
speed 115200 baud; rows 45; columns 169; line = 0;
  • Display only the current baud rate:
Board $> stty -F /dev/ttySTM1 speed
# uart3 (aka ttySTM1) baud rate is set to 115200 bps #
115200
  • Change the baud rate:

stty -F /dev/ttySTMx EXPECTED_BAUDRATE

Example: change the baud rate to 19200

# Change uart3 (aka ttySTM1) baud rate to 19200 bps #
Board $> stty -F /dev/ttySTM1 19200

The stty tool proposes many arguments allowing many operations on a tty terminal, such as:

  • special settings (various arguments such as speed, line discipline, minimum number of characters for a completed read, size, timeout, etc...)
  • control settings
  • input settings
  • output settings
  • local settings
  • combination settings


Note: If you want to go further, an interesting tutorial describes termios and stty [2].

4 Send / Receive data (with stty, minicom, echo and cat tools)[edit]

4.1 Default configuration (8 data bits frame, no parity errors detection, no framing errors detection)[edit]

Sending data can be simply done by opening the device as a file and writing data to it.

  • Configure a port on ttySTM1 (aka usart3)
Board $> stty -F /dev/ttySTM1 115200 -echo
  • Display the current configuration on ttySTM1 (usart3):
# display the configuration of uart3 (aka ttySTM1) #
Board $> stty -a -F /dev/ttySTM1
speed 115200 baud; rows 45; columns 169; line = 0;
  • Open a port on ttySTM1 (usart3) to receive data
Board $> cat /dev/ttySTM1 &
  • On the remote PC, identify the tty terminal associated to RS232 card connected on STM32MPU USART3 pins
# Command to execute from host terminal #
PC $> ls /dev/ttyUSB*

/dev/ttyUSB0

  • Open a minicom in a second terminal on the remote device connected on USART3 pins
PC $> minicom -D /dev/ttyUSB0
  • Display the current configuration on ttyUSB0 (remote device):
# Display the configuration of host uart (aka ttyUSB0) #
PC $> stty -a -F /dev/ttyUSB0
speed 115200 baud; rows 45; columns 169; line = 0;
  • Send data from remote PC to STM32MPU over USART3 with default termios configuration (8 frames length, no parity)
# Execute this command from host terminal #
PC $> echo "HELLO" > /dev/ttyUSB0
  • send data from STM32MPU to remote PC over USART3 with default termios configuration (8 frames length, no parity)
# Execute this command from STM32 terminal #
Board $> echo "HELLO" > /dev/ttySTM1

4.2 Parity errors detection[edit]

Some additional termios funtions allow to enable parity errors detection:

  • parenb: Parity enable
  • parodd: Odd parity else even
  • inpck: Enable input parity or framing check
  • ignpar: Ignore characters with parity or framing errors


Exemples:

  • Configure a port on ttySTM1 (usart3) with even parity enabling
# STM32 parity enabling #
Board $> stty -F /dev/ttySTM1 115200 -echo parenb -parodd inpck ignpar
  • Open a port on ttySTM1 (usart3) to receive data
Board $> cat /dev/ttySTM1 &
Open a minicom in a second terminal on the remote device connected on USART3 pins
PC $> minicom -D /dev/ttyUSB0
  • Configure a port on ttyUSB0 (remote device) with even parity enabling:
# Remote device parity enabling #
PC $> stty -a -F /dev/ttyUSB0 115200 -echo parenb -parodd inpck ignpar
speed 115200 baud; rows 45; columns 169; line = 0;
  • Send data from remote PC to STM32MPU over USART3 with default termios configuration (8 frames length, no parity)
# Execute this command from host terminal #
PC $> echo "HELLO" > /dev/ttyUSB0
  • send data from STM32MPU to remote PC over USART3 with default termios configuration (8 frames length, no parity)
#  Execute this command from STM32 terminal #
Board $> echo "HELLO" > /dev/ttySTM1


4.3 Framing errors detection[edit]

Some additional termios funtions allow to enable framing errors detection:

  • csize: Number of bits per byte (CS5, CS6, CS7, or CS8)
  • inpck: Enable input framing check
  • ignpar: Ignore characters with parity or framing errors


Exemples:

  • Configure a port on ttySTM1 (usart3) with framing check enabling and 7 data bits length frames
# STM32 framing enabling #
Board $> stty -F /dev/ttySTM1 115200 -echo cs7 inpck ignpar
  • Open a port on ttySTM1 (usart3) to receive data
Board $> cat /dev/ttySTM1 &
Open a minicom in a second terminal on the remote device connected on USART3 pins
PC $> minicom -D /dev/ttyUSB0
  • Configure a port on ttyUSB0 (remote device) with framing check enabling and 7 data bits length frames
# Remote device parity enabling #
PC $> stty -a -F /dev/ttyUSB0 115200 -echo cs7 inpck ignpar
speed 115200 baud; rows 45; columns 169; line = 0;
  • Send data from remote PC to STM32MPU over USART3 with default termios configuration (8 frames length, no parity)
# Execute this command from host terminal #
PC $> echo "HELLO" > /dev/ttyUSB0
  • send data from STM32MPU to remote PC over USART3 with default termios configuration (8 frames length, no parity)
# Execute this command from STM32 terminal #
Board $> echo "HELLO" > /dev/ttySTM1

5 Identify processes using a tty serial device (with fuser tool)[edit]

Board $> fuser /dev/ttySTM0
# The process numbered 395, 691 and 3872 are using a tty serial device #
395 691 3872

6 Link a tty serial device with a line discipline (with ldattach tool)[edit]

Attach ttySTM1 with line discipline number n :

Board $> ldattach n /dev/ttySTM1

7 File transfer over serial console[edit]

Please see the dedicated article How to transfer a file over serial console.

8 References[edit]

TeleTYpewriter

Microprocessor Unit

also known as

terminal input output structure

Attachments

Discussions