原创 原代码实例：Select() in ZRTOS

1、问题综述

在一款车载记录仪中，车载仪即可以通过无线传输的方式，也可以用有线（J1939中的Transport Protecol）传输的方式与办公室软件联系（上传记录的数据、下传命令、修改参数等）。因此，车载仪中的通讯软件模块将同时与两个以上通讯介质联络。ZRTOS 中 Select（）API 将很好地handle这种情况。以下是C代码:

#define COM_J1939    0
#define COM_WIRELESS 1
#define _SEL_TIME_OUT       3000 //30s time out 

static fd_set com_ch; //container for select
static RTOS_FD_TYPE com_in[2];

void com_init(void) //communication initialization
{   
  current_COM = COM_DISPATCH_LOGON;
  RTOS_FD_ZERO(&com_ch); //zero file descriptor - select() usage container

  com_in[COM_J1939] = open(J1939_COM_CH); //open J1939 Transport protecol com channel;
  RTOS_FD_SET(getFds(com_in[COM_J1939]), &com_ch);//put J1939 com channel into select() usage container
  com_in[COM_WIRELESS] = open(WIRELESS_COM_CH);//open wireless com channel;
  RTOS_FD_SET(getFds(com_in[COM_WIRELESS]), &com_ch);//put wireless com channel into select usage container
      
  com_process.sem = rtos_semBCreate(0, SEM_EMPTY); //greate a semaphone
  
  rtos_taskSpawn(COM_TASK_PRORITY-2, (RTOS_FUNCPTR) com_tasks, 0);//spawn a task to handle communication channels
  rtos_taskSpawn(COM_TASK_PRORITY-2, (RTOS_FUNCPTR) process_com_message, 0);//spawn a task to process communication messages

 }

static void com_tasks(void) //the task to handle communication channels
{
  long sel, size;

   
  sel = select(&com_ch, _SEL_TIME_OUT);  //select() with 30 s time out

#define _5MIN_TIME_OUT (10)   //if a cmd did not finish in 5 min. it was a fault cmd, get out any way
                               //if the connection was a j1939, the time out is 5 sec.
  
  
  if (sel == 0) { //time out
//do nothing or may use as a counter timer, when the number of the timeout reach a critical value, do something...

  } else {  //COM available
    if (RTOS_FD_ISSET(getFds(com_in[COM_J1939]), &com_ch)) { //J1939 chaneel active
      size = read(com_in[COM_J1939], (char *) com_receive, COM_RCV_BUFFER_SIZE);
    } else {  //wireless
      size = read(com_in[COM_WIRELESS], (char *) com_receive, COM_RCV_BUFFER_SIZE);
    }
    if (size > 0) {
      rtos_semGive(com_process.sem); //wake up process-communication-message task 
    }   

  }
  RTOS_FD_ZERO(&com_ch);//zero the select() container
}

static void process_com_message(void)//process-communication-message task 
{     
  rtos_semTake(com_process.sem, WAIT_FOREVER); 

//your process code here ...

//...

}

2、结论

ZRTOS中的select() 函数的使用方式和效果与vxWorks、UNIX基本相同。