Serial Programming
References
- Serial Programming HOWTO
- Serial Programming Guide for POSIX Operating System
- Serial Port Programming in Windows and Linux
How-To
Flush Serial Buffers
Use constant TCSAFLUSH for function tcsetattr (see [1] and [2]):
| Constant | Description |
|---|---|
| TCSANOW | Make changes now without waiting for data to complete |
| TCSADRAIN | Wait until everything has been transmitted |
| TCSAFLUSH | Flush input and output buffers and make the change |
This can be done even on a serial port that is already configured:
struct termios options;
tcgetattr(fd, &options); // Get current configuration of this port
cfsetispeed(&options, B115200); // Configure some port options (e.g. baud rate...)
...
tcsetattr(fd, TCSANOW, &options); // Apply the new settings immediately
... // Read / Write to the port...
tcsetattr(fd, TCSAFLUSH, &options); // Flush IO buffer
Tools
Minicom
Minicom (wikipedia) is a text-based modem control and terminal emulation program for Linux.
It can be used to debug / test serial connections, but unfortunately it is only ascii based and does not allow to send / receive easily data in hexadecimal format (except via sending / receiving files).
Minicom is in the repositories:
sudo apt-get install minicom
Cutecom
Cutecom is a handy and easy graphic tool to test/debug embedded devices controlled via serial link. This tool allows sending / receiving data in hexadecimal format.
Cutecom is in the repositories:
sudo apt-get install cutecom
interceptty
interceptty is a program that sits between a serial port (or other tty-style device) and an application, and logs everything that passes through it.
SerLook
SerLook is a KDE application for inspecting data going over serial lines.
Troubleshooting
Shunt RXD/TXD pin
An easy way to test whether the serial line is working properly is simply to shunt the RXD and TXD line of the serial connector (2nd and 3rd pin on a typical DE9 RS232 connector). This way anything sent to the serial port is echoed back.
- Open a terminal connected to the serial port,
- Shunt RXD and TXD (2nd and 3rd pin),
- Type character and verify that the same character are echoed back.
_______________________
/ 1 5 \
\ o o o o o /
\ 6 9 /
\ o o o o /
\_________________/
|
On a D-sub DE9 RS232 connector, the top left pin is the 1st pin, the bottom right is the 9th pin. The pinout is as follows:
|