We can use socat to create 2 virtual serial ports that are connected to each
other locally. This can be useful for debugging serial port applications. Or
simulating serial port communication. Or running 2 legacy programs that only
communicate with each other over serial ports, such as old DOS games. And of
course, for education, since serial communication is probably the most simple
communication protocol there is, RS232 is considered at the bottom of the OSI
stack, at the "Physical Layer". See: http://electronics.stackexchange.com/questions/31171/internet-vs-serial-communication
> # create 2 pseudo ttys that are raw, and with echo disabled
> socat -d -d pty,raw,echo=0 pty,raw,echo=0 &
[1] 4952
2016/04/29 00:47:08 socat[548] N PTY is /dev/pty1
2016/04/29 00:47:08 socat[548] N PTY is /dev/pty3
2016/04/29 00:47:08 socat[548] N starting data transfer loop with FDs [5,5] and [7,7]
> stty --file=/dev/pty1
speed 38400 baud; line = 0;
min = 1; time = 0;
-brkint -icrnl -imaxbel
-opost
-isig -icanon -echo
> stty --file=/dev/pty3 -a
speed 38400 baud; rows 0; columns 0; line = 0;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>; eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R;
werase = ^W; lnext = ^V; discard = ^O; min = 1; time = 0;
-parenb -parodd -cmspar cs8 -hupcl -cstopb cread -clocal -crtscts
-ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany -imaxbel -iutf8
-opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0
-isig -icanon iexten -echo echoe echok -echonl -noflsh -xcase -tostop -echoprt echoctl echoke -flusho -extproc
> # run picocom mapping \r to \r\n when writing to serial port, and enabling local echo so you can see what you type
> picocom --baud 38400 --omap crcrlf --echo /dev/pty1
picocom v2.2a
port is : /dev/pty1
flowcontrol : none
baudrate is : 38400
parity is : none
databits are : 8
stopbits are : 1
escape is : C-a
local echo is : yes
noinit is : no
noreset is : no
nolock is : no
send_cmd is : sz -vv
receive_cmd is : rz -vv -E
imap is :
omap is : crcrlf
emap is : crcrlf,delbs,
Type [C-a] [C-h] to see available commands
Terminal ready
Now launch a second terminal:
> picocom --baud 38400 --omap crcrlf --echo /dev/pty3
Now you can type to each other!
For discussion of baud vs bits per second, see: http://www.tldp.org/HOWTO/Modem-HOWTO-23.html
This is actually a form of:
- https://en.wikipedia.org/wiki/Null_modem#Virtual_null_modem or https://en.wikipedia.org/wiki/COM_port_redirector#VIRTUAL
It appears that picocom sets its own settings on the terminal device, while
saving the original settings to be restored once picocom exits. This does mean
that if you run stty -F /dev/pty1 cs5, picocom will reset it by default to
cs8, and once it exits, it will restore it back to cs5. There's not much
point in setting these flags in stty then, as you will need to set them in
picocom anyway. This behaviour can be changed with --noinit flag.
Note that input mapping in picocom refers to mapping bytes from reading the serial
port. While output mapping means mapping from STDIN to serial port. Finally echo
mapping means mapping characters from STDIN to STDOUT.