Signal是一种处理异常或异步改变执行流程的机制，类似于软中断。与POSIX兼容，VxWorks也定义了多种Signal(0为NULL Signal)

#define SIGHUP     1 /* hangup */
#define SIGINT     2 /* interrupt */
#define SIGQUIT    3 /* quit */
#define SIGILL     4 /* illegal instruction (not reset when caught) */
#define SIGTRAP    5 /* trace trap (not reset when caught) */
#define SIGABRT    6 /* used by abort, replace SIGIOT in the future */
#define SIGEMT     7 /* EMT instruction */
#define SIGFPE     8 /* floating point exception */
#define SIGKILL    9 /* kill */
#define SIGBUS    10 /* bus error */
#define SIGSEGV   11 /* segmentation violation */
#define SIGFMT    12 /* STACK FORMAT ERROR (not posix) */
#define SIGPIPE   13 /* write on a pipe with no one to read it */
#define SIGALRM   14 /* alarm clock */
#define SIGTERM   15 /* software termination signal from kill */
#define SIGCNCL   16 /* pthreads cancellation signal */
#define SIGSTOP   17 /* sendable stop signal not from tty */
#define SIGTSTP   18 /* stop signal from tty */
#define SIGCONT   19 /* continue a stopped process */
#define SIGCHLD   20 /* to parent on child stop or exit */
#define SIGTTIN   21 /* to readers pgrp upon background tty read */
#define SIGTTOU   22 /* like TTIN for output if (tp->t_local&LTOSTOP) */

#define SIGRES1   23 /* reserved signal number (Not POSIX) */
#define SIGRES2   24 /* reserved signal number (Not POSIX) */
#define SIGRES3   25 /* reserved signal number (Not POSIX) */
#define SIGRES4   26 /* reserved signal number (Not POSIX) */
#define SIGRES5   27 /* reserved signal number (Not POSIX) */
#define SIGRES6   28 /* reserved signal number (Not POSIX) */
#define SIGRES7   29 /* reserved signal number (Not POSIX) */

#define SIGUSR1   30 /* user defined signal 1 */
#define SIGUSR2   31 /* user defined signal 2 */

#define SIGPOLL   32 /* pollable event */
#define SIGPROF   33 /* profiling timer expired */
#define SIGSYS    34 /* bad system call */
#define SIGURG    35 /* high bandwidth data is available at socket */
#define SIGVTALRM 36 /* virtual timer expired */
#define SIGXCPU   37 /* CPU time limit exceeded */
#define SIGXFSZ   38 /* file size time limit exceeded */

#define SIGEVTS   39 /* signal event thread send */
#define SIGEVTD   40 /* signal event thread delete */

#define SIGRTMIN  48 /* Realtime signal min */
#define SIGRTMAX  63 /* Realtime signal max */

#define _NSIGS    63

任务或ISR可以发送Signal到任务本身或其它任务；而对方可以根据Signal Mask选择接收还是忽略该Signal。如果要接收的话，需要注册Signal的处理函数

发送Signal时，使用的是发送者的上下文。而处理函数在处理接收到的Signal时，使用的是接收者的上下文。即使接收者阻塞或者挂起了，这个处理还是会执行的。

Signal的处理函数中可以调用的系统函数有这些