termiWin

~ A termios porting for Windows ~

Current Version 1.2.1 (16/11/2020)

termiWin

Introduction

termiWin is a library which purpose is to allow you to use on a Windows system, the same code used in Linux to communicate with a device through a serial port. This is possible because termios’s functions have been rewritten to be compatible with Windows’s COM functions.

Implementation

It's enough to include termios.h, termiWin.h and termiWin.c to build the project. You don't have to change anything else in your code

Supported Build Platform

Visual C++ (> 12.0)
- Build and works fine without any restriction
Visual C++ (< 12.0)
- Not tested, if you want you can report a working build on an older compiler. I will appreciate your contribution.
MinGW
- Requires -D TERMIWIN_DONOTREDEFINE to build (which means that open, close, select etc must be replaced with openSerial, closeSerial, ...), but works fine afterall and it's used on my travis configuration

Library Architecture

The termios Structure

This is the main structure of the library and it’s often passed as argument to the functions, it has the following members:

tcflag_t c_iflag; /*input modes*/
tcflag_t c_oflag; /*output modes*/
tcflag_t c_cflag; /*control modes*/
tcflag_t c_lflag; /*local modes*/
cc_t c_cc[NCCS]; /* special character */

where tcflag_t is defined as an unsigned integer.

The members of termios structure are used to set and retrieve the serial port configuration parameters.
There five types of flags, sorted by mode; they are implemented in the same way as they are in termios, except for some, which are not used.

Input modes flags

INPCK – Not implemented, use PARENB instead.
IGNPAR – Not implemented, disable PARENB instead.
PARMRK – Not implemented, use PARENB instead.
ISTRIP – Not implemented, use CS7 instead.
IGNBRK – Not implemented.
IGNCR – Not implemented.
ICRNL – Not implemented.
INLCR – Not implemented.
IXOFF - If this bit is set, start/stop control on input is enabled. In other words, the computer sends STOP and START characters as necessary to prevent input from coming in faster than programs are reading it. The idea is that the actual terminal hardware that is generating the input data responds to a STOP character by suspending transmission, and to a START character by resuming transmission.
IXON - If this bit is set, start/stop control on output is enabled. In other words, if the computer receives a STOP character, it suspends output until a START character is received. In this case, the STOP and START characters are never passed to the application program. If this bit is not set, then START and STOP can be read as ordinary characters.

Local modes flags

Since there’s no way to implement them in Windows, they have asbolutely no effect using termiWin, but you can keep the same you use in Linux for compatibilty.

Control modes flags

CSTOPB - If this bit is set, two stop bits are used. Otherwise, only one stop bit is used.
PARENB - If this bit is set, generation and detection of a parity bit are enabled.
PARODD - This bit is only useful if PARENB is set. If PARODD is set, odd parity is used, otherwise even parity is used.
CSIZE - This is a mask for the number of bits per character.
CS5 - This specifies five bits per byte.
CS6 – This specifies six bits per byte.
CS7 – This specifies seven bits per byte.
CS8 – This specifies eight bits per byte.
CLOCAL – Is used in termios for ignoring the data carrier detected, but in Windows it can't be implemented
CREAD – In termios, if not set, no character will be received, but in Windows it can't be implemented

Output modes flags

Since there’s no way to implement them in Windows, they have asbolutely no effect using termiWin, but you can keep the same you use in Linux for compatibilty.

Special character array

VEOF – Is the EOF character to be used during the communication.
VEOL – Not implemented.
VERASE – Not implemented.
VINTR – Interrupt character.
VKILL – Not implemented.
VMIN – If set to 0, the port is set to not-blocking, otherwise to blocking.
VQUIT – Not implemented.
VSTART – Not implemented.
VSTOP – Not implemented.
VSUSP – Not implemented.
VTIME – Timeout for reading operations when COM is set to not-blocking.

Serial configuration functions

tcgetattr

int tcgetattr(int fd, struct termios *termios_p)

Sets in the internal DCB structures the current serial port parameters, it always has to be invoked before using tcsetattr.
Returns 0 if succeded, otherwise -1.

tcsetattr

int tcsetattr(int fd, int optional_actions, struct termios *termios_p)

Reads the flags set in the termios structure and sets the properly parameters in the DCB structure and eventually it applies the parameters to the serial port.
Returns 0 if succeded, otherwise -1.

tcsendbreak

int tcsendbreak(int fd, int duration)

Sends a break character to the serial port; duration is not implemented.
Returns 0 if succeded, otherwise -1.

tcdrain

int tcdrain(int fd)

Waits until all output written to the serial port has been transmitted.
Returns 0 if succeded, otherwise -1.

tcflush

int tcflush(int fd, int queue_selector)

Discards data on serial port. queue_selector can assume the following values:

TCIFLUSH (discards data received but still not read).
TCOFLUSH (discards data written but still not transmitted),
TCIOFLUSH (discards both data received but still not read and data written but still not transmitted).

Returns 0 if succeded, otherwise -1.

tcflow

int tcflow(int fd, int action)

Suspends transmission or receptions of data on serial port based on action. Action can assume the following values:

TCOON restarts suspended output.
TCIOFF transmits a STOP character.
TCION transmits a START character.
TCOOF suspends output.

Returns 0 if succeded, otherwise -1.

cfmakeraw

void cfmakeraw(struct termios *termios_p)

Sets but doesn’t commit the following options for the serial port:

Charset: 8 bits
StopBits: one stop bit
Parity: no parity

Use tcsetattr to commit them.

cfgetispeed

speed_t cfgetispeed(const struct termios *termios_p)

Returns the input speed, speed can assume the same values of termios (B9600, B115200, …).

cfgetospeed

speed_t cfgetospeed(const struct termios *termios_p)

returns the output speed, speed can assume the same values of termios (B9600, B115200, …).

cfsetispeed

int cfsetispeed(struct termios *termios_p, speed_t speed)

Sets, but doesn’t commits the parameter of speed for the serial port (in Windows there’s no distinction between input/output /control), speed can assume the same values of termios (B9600, B115200, …).
Returns 0 if succeded, otherwise -1.

cfsetospeed

int cfsetospeed(struct termios *termios_p, speed_t speed)

cfsetsspeed

int cfsetsspeed(struct termios \*termios_p, speed_t speed)

Supported speed

The supported speeds are the the following (not all speeds could be implemented since some of them can't be used in a Windows environment)

B110
B300
B600
B1200
B2400
B4800
B9600
B19200
B38400
B57600
B115200

Extra functions

You can use open/close/write/read instead of these names by default. If it causes to you conflicts with another library you can deactivate these definitions defining in your project:

#define TERMIWIN_DONOTREDEFINE

open_serial

int open_serial(const char* portname, int opt)

Open the serial port which name is portname with opt set for the port to be read only, write only or both read/write (O_RDONLY, O_WRONLY, O_RDWR). Returns the file descriptor (fd is actually useless in Windows with serial ports, but is set for compatibilty). The function can be called using open instead of openSerial (for termios compatibilty).
The portname must be in the format "COMnumber" (e.g. COM2, COM11).

close_serial

int close_serial(int fd)

Closes the serial port. Returns 0 if succeded, otherwise -1. The function can be called using close instead of closeSerial. (for termios compatibilty).

write_serial

ssize_t write_serial(int fd, const void* buffer, size_t count)

Writes to serial “count” characters contained in buffer. Returns the number of transmitted characters or -1 if transmission failed. The function can be called using write instead of writeToSerial (for termios compatibilty).

read_serial

ssize_t read_serial(int fd, void* buffer, size_t count)

Reads “count” bytes from serial port and put them into buffer. Returns the number of read bytes or -1 if read failed. The function can be called using read instead of readFromSerial (for termios compatibilty).

select_serial

int select_serial(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout)

It behaves as termios select. Returns the file descriptor ready for the chosen operation or -1 if failed. The function can be called using select instead of selectSerial (for termios compatibility).

getHandle

HANDLE getHandle()

Returns the HANDLE from the COM structure.

Multiple serial communications

At the moment is not possible to have more than one serial communication at the same time. I have never implemented this feature and probably I won't.

What is termiWin intended for

termiWin is just a simple library which executes termios functions using Windows libsock functions, because of that, any particular behaviour in the communication with the serial device, could not work properly. termiWin is intended just for simple communications.

When termiWin can be a good choice? ✅

✅ - When you have to do a quick project without particular requirements.
✅ - When you don't need performance and high reliability.
✅ - When the communication between you and the serial device doesn't require a particular configuration.

When termiWin is NOT a good choice? ❌

❌ - When you need multiple device communications. termiWin just doesn't support this feature at the moment.
❌ - When you need performance - since termiWin has to convert termios to windows instructions, it won't be faster than a program with windows instructions wrote by the developer.
❌ - When you require particular configuration and to use particular functions (such as tcdrain, tcflush etc) - they could work, but I can't assure

Contributions

Everybody can contribute to this project, indeed any improvement will be appreciated.

Changelog

View CHANGELOG

License

termiWin is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. termiWin is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with termiWin.
If not, see http://www.gnu.org/licenses/.

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