====== Possible alternatives for virtual serial ports ======

  * Pseudo teletype -- Linux C programming
  * socat -- Command
  * fuse -- Filesystem in userspace
  * <del>named pipes -- Heave data between processes</del> <color #ed1c24>One-way</color>


^ Method ^ Description ^ Pros ^ Cons ^ Dependencies ^
| pty    | Virtual terminal device | Full duplex     | Must create links to name them         | native      |
| socat  | Multipurpose relay      | Super flexible  | External program.\\ Maybe less control | socat       |
| fuse   | Filesystem in userspace | ??              | ????                                   | libfuse-dev |
| fifo   | Named pipes             | Simple          | One-way only                           | native      |
====== Scratchpad ======

[[https://www.gnu.org/software/libc/manual/pdf/libc.pdf|glibc manual]] -- Innehåller massa bra info!

[[https://linux.die.net/man/3/termios|termios man page]]

[[https://linux.die.net/man/4/tty_ioctl|tty_ioctl man page]]

[[http://kirste.userpage.fu-berlin.de/chemnet/use/info/libc/libc_12.html#SEC237|Seting up terminals]]

[[https://www.cmrr.umn.edu/~strupp/serial.html|Serial programming guide for posix]]

<code>
errno
termios
tcgetattr 
cfsetospeed 
cfsetispeed 
tcsetattr 
posix_openpt
ioctl_tty

Använd noncanonical input processing mode för att kunna styra RTS och DTR

termios.h är en grej



#include <errno.h>
#include <fcntl.h> 
#include <string.h>
#include <termios.h>
#include <unistd.h>

gör open på porten
int fd = open (portname, O_RDWR | O_NOCTTY | O_SYNC);
</code>

Get info:

<code>
$ dmesg | egrep --color 'serial|ttyS'
</code>

Some commands to manage, read and write to the serial port
<code>
# Print info
$ setserial -g /dev/ttyS0

# Using cu (call-up). Exit by typing ~.
$ cu -l /dev/ttyS0 -s 115200

# Using screen. Exit with c-a k
$ screen /dev/ttyS0 115200

# Read current configuration using stty
$ stty -a < /dev/ttyS0
# or
$ stty -a -F=/dev/ttyS0

# Set baud rate and hardware flow control using stty
$ stty -F=/dev/ttyS0 9600 crtscts ixon

</code>

[[https://man7.org/linux/man-pages/man2/poll.2.html|Polla för satan!]]

[[https://man7.org/linux/man-pages/man7/signal.7.html|Läs på om signaler!]]



====== Serial port basics ======
{{ :linux:serial.jpg?400|}}

|DTE | Data terminal equipment (computer/MCU) |
|DCE | Data circuit-terminating equipment (modem/device) |
|RTS | Request to send |
|CTS | Clear to send |
|DTR | Data terminal ready |
|DSR | Data set ready |

{{:linux:db9-pinout.gif?400 |}}


====== Accessing a serial port ======



====== Pseudo teletype ======