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Asked: 2026-06-03T22:34:47+00:00

all, when debugging embedded system, as you know, we usually communicate target device over

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all,

when debugging embedded system, as you know, we usually communicate target device over an uart console. Now I want to test “Magic sysrq” function in linux kernel, which need to send a “break” to console driver. I’ve found what does the “break” mean, seems I need to keep TX-line electrical low level for a while.
My question is how to send this break “character”, from APUE(Advanced program in unix), I have to call function “tcsendbreak”, which mean i have to write a program. I wander if i can use some specical keys to send that, like ^C etc.
Don’t methon “echo “x” > /proc/sysrq-trigger””, I know that, just have a discussion on other way 🙂

This is my terminal settings, I talk with target with ckermit. 

stty -a < /dev/ttyUSB0 
speed 115200 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  
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1 Answer

  1. Editorial Team

    From the documentation, it looks like Control-\ B will send a break in C-Kermit.

    Other ways…

    One way to send a break is to:

    1. Switch to a lower speed
    2. Send a Nul (0) or an @ (4016) — a character with many contiguous 0 bits will produce the framing error called a BREAK.
    3. Switch back to the original speed

    As you noted, the other way is to use the <termios.h> line control
    functions.

    #include <termios.h>

int tcsendbreak(int fildes, int duration); // "duration" is ignored
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