基于嵌入式操作系统VxWorks的

Posted 2020-12-15

管道可以看作受驱动器pipeDrv管理的虚拟I/O设备，使用基本的I/O系统接口可以读、写和操作管道，这些函数包括read、write、open、close、ioctl和select等。与pipe密切相关的其它API还有：
（1）pipeDrv(?)：初始化pipeDrv，函数原型：
STATUS pipeDrv (void);
（2）pipeDevCreate(?)：创建pipe，函数原型：
STATUS pipeDevCreate
??? (
??? char name,????????????? / 创建的pipe名 /
??? int??? nMessages,???????? / pipe中的最大消息数 /
??? int??? nBytes???????????? / 每个消息的大小 /
??? );
（3）pipeDevDelete：删除pipe，函数原型：
STATUS pipeDevDelete
??? (
??? char name,????????????? / 要删除的pipe名 /
??? BOOL?? force????????????? / 如果为真，则强制删除pipe /
??? );
下面我们看看pipe使用的demo：
例3：管道
/ includes /
#include "vxWorks.h"
#include "taskLib.h"
#include "stdio.h"
#include "ioLib.h"
#include "pipeDrv.h"
?
/globals /
typedef struct
{
? VOIDFUNCPTR routine;?? / 函数指针 /
? int arg;
} MSG_REQUEST; / message structure /
?
#define TASK_PRI????????? 254???????????? / tServers task‘s priority /
#define TASK_STACK_SIZE? 5000????? / tServer task‘s stack size /
#define PIPE_NAME?????? "/pipe/server"? / name of the pipe device /
#define NUM_MSGS? 10???? / max number of messages in the pipe /
?
LOCAL int pipeFd; / File descriptor for the pipe device /
LOCAL void pipeServer(); / server task /
?
/ serverStart：初始化pipeServer任务以执行管道中夹带的函数 /
STATUS serverStart()
{
? if (pipeDevCreate(PIPE_NAME, NUM_MSGS, sizeof(MSG_REQUEST)) == ERROR)
? {
??? perror("Error in creating pipe"); / print error if pipe is already
???? created, but do not return /
? }
?
? / Open the pipe /
? if ((pipeFd = open(PIPE_NAME, UPDATE, 0)) == ERROR)
? {
??? perror("Error in opening pipe device");
??? return (ERROR);
? }
?
? / Spawn the server task /
? if (taskSpawn("tServer", TASK_PRI, 0, TASK_STACK_SIZE, (FUNCPTR)pipeServer, 0,
??? 0, 0, 0, 0, 0, 0, 0, 0, 0) == ERROR)
? {
??? perror("Error in spawning tServer task");
??? close(pipeFd);
??? return (ERROR);
? }
?
? return (OK);
}
?
/ serverSend ：发送管道消息，将函数指针作为消息的一部分 /
STATUS serverSend(VOIDFUNCPTR routine, / name of the routine to execute / int arg / argument of the routine /
)
{
? MSG_REQUEST msgRequest;
? int status;
?
? / Initialize the message structure /
? msgRequest.routine = routine;
? msgRequest.arg = arg;
?
? / Send the message and return the results /
? status = write(pipeFd, (char) &msgRequest, sizeof(MSG_REQUEST));
?
? return ((status == sizeof(MSG_REQUEST)) ? OK : ERROR);
}
?
/ pipeServer：读取管道消息并执行管道消息中夹带的函数 /
LOCAL void pipeServer()
{
? MSG_REQUEST msgRequest;
?
? while (read(pipeFd, (char) &msgRequest, sizeof(MSG_REQUEST)) > 0)
??? (msgRequest.routine)(msgRequest.arg);
}
?? 上述程序中，pipeServer执行于非常低的优先级(254级)，当我们在shell中输入“serverSend(VOIDFUNCPTR routine, int arg)” 时，pipeServer将读到管道中的消息，并执行“routine (arg)”。
?????? 为对此进行验证，我们在程序中再添加一个函数：
void PRINT(int arg)
{
?????? printf("%d",arg);
}
当我们在tShell中输入“serverSend(PRINT,2);”，在VxSim中将输出2。
9.套接字
不论网络中的节点使用什么操作系统，套接字的通信都是完全对等的。套接字有两种：
（1）流套接字（SOCK_STREAM，采用TCP协议）：流套接字提供了双向的、有序的、无重复并且无记录边界的数据流服务；
（2）数据报套接字（SOCK_DGRAM，采用UDP协议）：数据报套接字也支持双向数据传输，但并不保证是可靠、有序和无重复的。
另外还有一种RAW套接字，但不常见。
VxWorks中与Socket相关的函数有：
（1）socket()：创建套接字?? ，原型为：
int socket
??? (
??? int domain,??? / address family (for example, AF_INET) /
??? int type,????? / SOCK_STREAM, SOCK_DGRAM, or SOCK_RAW /
??? int protocol?? / socket protocol (usually 0) /
??? );
（2）bind()：给套接字绑定名称 ，原型为：
STATUS bind
??? (
??? int?????????????? s,????? / socket descriptor /
??? struct sockaddr name,?? / name to be bound /
??? int??????????? namelen / length of name /
??? );
（3）listen()：服务端监听TCP连接请求，原型为：
STATUS listen
??? (
??? int s,??????????????????? / socket descriptor /
??? int backlog?????????????? / number of connections to queue /
??? );
（4）accept()：服务端接受TCP连接请求，原型为：
int accept
??? (
??? int?? ?????????s,????? / socket descriptor /
??? struct sockaddr addr,?? / peer address /
??? int ?????????? addrlen / peer address length /
??? );
（5）connect()：客户端请求连接套接字，原型为：
STATUS connect
??? (
??? int?????????????? s,????? / socket descriptor /
??? struct sockaddr name,?? / addr of socket to connect /
??? int??????????? namelen / length of name, in bytes /
??? );
（6）shutdown()：关闭套接字间连接，原型为：
STATUS shutdown
??? (
??? int s,??? ????????????/ socket to shut down /
??? int how ???????????? / 0:receives disallowed;1:sends disallowed;
2:sends and receives disallowed /
??? );
（7）sendto()、send()、sendmsg()：发送数据
int sendto
??? (
??? int?????????????? s,????? / socket to send data to /
??? caddr_t?????????? buf,??? / pointer to data buffer /
??? int????? ?????????bufLen, / length of buffer /
??? int?????????????? flags,? / flags to underlying protocols /
??? struct sockaddr to,???? / recipient‘s address /
??? int?????????????? tolen?? / length of to sockaddr /
??? );
?
int send
??? (
??? int????? ????s,?????????? / socket to send to /
??? const char buf,???????? / pointer to buffer to transmit /
??? int????????? bufLen,????? / length of buffer /
??? int????????? flags??????? / flags to underlying protocols /
??? );
?
int sendmsg
??? (
??? int???????????? sd,?????? / socket to send to /
??? struct msghdr mp,?????? / scatter-gather message header /
??? int???????????? flags???? / flags to underlying protocols /
??? );
（8）recvfrom ()、recv ()、recvmsg ()：接收数据
int recvfrom
??? (
??? int? ?????????????s,?????? / socket to receive from /
??? char ??????????? buf,???? / pointer to data buffer /
??? int?????????????? bufLen,? / length of buffer /
??? int?????????????? flags,?? / flags to underlying protocols /
??? struct sockaddr from,??? / where to copy sender‘s addr /
??? int ???????????? pFromLen / value/result length of from /
??? );
?
int recv
??? (
??? int??? s,???????????????? / socket to receive data from /
??? char buf,?????????????? / buffer to write data to /
?? ?int??? bufLen,??????????? / length of buffer /
??? int??? flags????????????? / flags to underlying protocols /
??? );
?
int recvmsg
??? (
??? int???????????? sd,?????? / socket to receive from /
??? struct msghdr mp,?????? / scatter-gather message header /
??? int???????????? flags???? / flags to underlying protocols /
??? );
限于篇幅的关系，我们在此不在列举socket通信的例子。但在最后一次连载的综合实例中，将包括完整的socket通信过程源代码。
10.信号与异常处理
信号是VxWorks中用于异常处理的方式，信号的驱动和执行机制有点类似于硬件中断（可以认为是一种软件上的通告，即software notification）。信号的生存期为从“产生”到“传递”，一个“产生”而未“传递”的信号处于pending状态。信号适宜进行异常处理，任务间的通信不要使用信号。
下面是从Embry-Riddle Real-Time Laboratory试验课程中获得的一个signal的例子：
例4：信号与异常处理
/ includes /
#include "vxWorks.h"
#include "sigLib.h"
#include "taskLib.h"
#include "stdio.h"
?
/ function prototypes /
void catchSIGINT(int);
void sigCatcher(void);
?
/ globals /
#define NO_OPTIONS 0
#define ITER1 100
#define LONG_TIME 1000000
#define HIGHPRIORITY 100
#define LOWPRIORITY 101
int ownId;
?
void sigGenerator(void) / task to generate the SIGINT signal /
{
? int i, j, taskId;
? STATUS taskAlive;
?
? if ((taskId = taskSpawn("signal", 100, 0x100, 20000, (FUNCPTR)sigCatcher, 0,??? 0, 0, 0, 0, 0, 0, 0, 0, 0)) == ERROR)
??? printf("taskSpawn sigCatcher failed ");
?
? ownId = taskIdSelf(); / get sigGenerator‘s task id /
?
? taskDelay(30); / allow time to get sigCatcher to run /
?
? for (i = 0; i < ITER1; i++)
? {
??? if ((taskAlive = taskIdVerify(taskId)) == OK)
??? {
????? printf("+++++++++++++++++++++++++++++++SIGINT sinal generated ");
????? kill(taskId, SIGINT); / generate signal /
????? / lower sigGenerator priority to allow sigCatcher to run /
????? taskPrioritySet(ownId, LOWPRIORITY);
??? }
??? else
???? / sigCatcher is dead */
????? break;
? }
? printf(" sigGenerator Exited ");
}
?
void sigCatcher(void) / task to handle the SIGINT signal /
{
? struct sigaction newAction;
? int i, j;
?
? newAction.sa_handler = catchSIGINT; / set the new handler /
? sigemptyset(&newAction.sa_mask); / no other signals blocked /
? newAction.sa_flags = NO_OPTIONS; / no special options /
?
? if (sigaction(SIGINT, &newAction, NULL) ==? - 1)
??? printf("Could not install signal handler ");
?
? for (i = 0; i < ITER1; i++)
? {
??? for (j = 0; j < LONG_TIME; j++)
????? ;
??? printf("Normal processing in sigCatcher ");
? }
?
? printf(" +++++++++++++++sigCatcher Exited+++++++++++++++ ");
}
?
void catchSIGINT(int signal) / signal handler code /
{
? printf("-------------------------------SIGINT signal caught ");
? / increase sigGenerator priority to allow sigGenerator to run /
? taskPrioritySet(ownId, HIGHPRIORITY);
}
分析以上程序，kill()函数产生信号，其原型为：
int kill
??? (
??? int tid,????????????????? / task to send signal to /
??? int signo???????????????? / signal to send to task /
??? );
sigaction()函数将信号与信号处理函数进行绑定，一个信号处理函数类似于程序中的catchSIGINT函数，一般结构为：
void sigHandlerFunction(int signalNumber)
{
... / signal handler code /
}
sigaction()函数的原型为：
int sigaction
??? (
??? int?????????????? signo, / signal of handler of interest /
??? const struct sigaction pAct,? / location of new handler /
??? struct sigaction ?? pOact? / location to store old handler /
??? );
?signo为信号序号，而输入参数pAct中存放的是信号处理函数的信息，pOact是一个输出参数，可以获得老的信号处理函数信息。
运行上述程序，输出结果为：
Normal processing in sigCatcher?
…???? //大量的Normal processing in sigCatcher
Normal processing in sigCatcher?
+++++++++++++++sigCatcher Exited+++++++++++++++
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