串口通信

Serial ports in linux can be found at /dev/ttyS[0123]. (USB to Serial converters may appear as something like /dev/ttyUSB0).

To know which serial port is enabled, run:

dmesg | grep tty

and you might see something like:

[    0.000000] console [tty0] enabled
[    0.567116] 00:04: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A

As shown, ttyS0 is available on this system. To show information about this serial port, run:

stty -F /dev/ttyS0 -a # you may need root previlidge

An example of infomation shown could be

speed 9600 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; flush = ^O; min = 1; time = 0;
-parenb -parodd 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

To interact with a serial port, you may use BoostAsio as well.

#include <boost/asio.hpp>
#include <boost/asio/serial_port.hpp>

boost::asio::serial_port sp;
sp.open("/dev/ttyS0");
sp.set_option(boost::asio::serial_port::baud_rate(9600));
sp.set_option(boost::asio::serial_port::flow_control(flow_control::none));
sp.set_option(boost::asio::serial_port::parity(parity::none));
sp.set_option(boost::asio::serial_port::stop_bits(stop_bits::one));
sp.set_option(boost::asio::serial_port::character_size(8));

Then you can use (async_)read(), (async_)write() to read/write from/to the serial port. Or you can call the port’s member function (async_)read_some() and (async_)write_some() to read/write some data from/to the port just like network sockets.

Error: Permission denied

See http://askubuntu.com/a/210230

The tty devices belong to the "dialout" group. You are not a member of this group and hence are denied access to /dev/ttyS0. So you need to add yourself to that group.

First check if you are a member of that group:

groups ${USER}

And you get output like:

qingpei : qingpei wheel

If you don’t belong to the dialout group, add yourself to it:

sudo gpasswd --add ${USER} dialout

You need to log out and log back in for it to take effect.