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我有一個從串口讀取和寫入的程序。我有讀取器線程讀取數據並將信息提供給共享內存。閱讀器線程應該休眠直到數據可用。所以我想讓read()
系統調用阻塞調用線程。考慮到手冊頁,除非您提供O_NONBLOCK
至open
,否則read
應始終阻止。但我有一個活動的線程,它在read
不斷返回-1
。同時更改VTIME
和VMIN
沒有什麼區別。這是口的打開方式:強制讀取系統調用塊
fd = open(portName.str().c_str()/*/dev/ttyS2*/, O_RDWR | O_NOCTTY);
if (fd < 0) // if open is not successful
{
cerr << ERROR << "Unable to open `" << portName << "'." << endl;
return false;
}
else
{
cout << INFO << "Port " << portName.str() << " successfully opened."
<< endl;
cout << INFO << "Configuring port..." << endl;
fcntl(fd, F_SETFL,0);
struct termios port_settings; // structure to store the port settings in
cfsetispeed(&port_settings, B38400); // set baud rate
cfsetospeed(&port_settings, B38400); // set baud rate
port_settings.c_cflag |= CLOCAL | CREAD;
port_settings.c_cflag &= ~CRTSCTS; // disable H/W flow control
port_settings.c_lflag &= ~(ISIG | // disable SIGxxxx signals
IEXTEN | // disable extended functions
ECHO | ECHOE); // disable all auto-echo functions
port_settings.c_lflag &= ~ICANON ; // raw mode
port_settings.c_oflag &= ~OPOST; // raw output
port_settings.c_iflag &= ~(IXON | IXOFF | IXANY); // disable S/W flow control;
// Following values do not change timout in runtime:
port_settings.c_cc[VTIME] = 2; // wait 0.2 second to get data -
port_settings.c_cc[VMIN] = 0;
port_settings.c_cflag = (port_settings.c_cflag &= ~CSIZE) | CS8; // set data byte size
port_settings.c_cflag &= ~CSTOPB; // set stop bit 1
port_settings.c_cflag &= ~PARENB; // set no parity
port_settings.c_iflag |= IGNPAR; // ignore parity
port_settings.c_iflag &= ~(INPCK | ISTRIP | PARMRK);
// Set
if (tcsetattr(fd, TCSANOW, &port_settings) < 0)
{
cerr << ERROR << "Unable to configure serial port." << endl;
return false;
}
else
{
cout << INFO << "Port `" << portName.str()
<< "' configuration was successful." << endl;
}
而且在讀線程:
byte buffer[256];
while (true)
{
int packetSize = read(fd, buffer, 256);
if (packetSize > 0)
{
// use data - this code is never run
}
else
{
// print error - we're always here. no matter how long timout is
}
}
感謝您的回覆。我用'perror'測試,結果是'無效參數' –
這意味着'fd'不是一個有效的文件描述符。 – Barmar
...和errno是'EBUSY(16)' –