set low latency serial port

jaxxzer · Oct 29, 2019 · b38f746 · b38f746
1 parent 64f63d4
commit b38f746
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diff --git a/com-handle.cpp b/com-handle.cpp
@@ -1,9 +1,68 @@
 #include <com-handle.h>
 
 #include <QDebug>
+
+    #include <sys/ioctl.h>
+    #include <termios.h>
+    #include <linux/serial.h>
+
+bool ComHandle::setLowLatency()
+{
+    auto handle = serialPort->handle();
+
+    if(!handle) {
+        qWarning() << "Failed to get serial handle from OS.";
+        return false;
+    }
+
+    // Our first attempt is with termios2
+    struct termios2 {
+        tcflag_t c_iflag;       /* input mode flags */
+        tcflag_t c_oflag;       /* output mode flags */
+        tcflag_t c_cflag;       /* control mode flags */
+        tcflag_t c_lflag;       /* local mode flags */
+        cc_t c_line;            /* line discipline */
+        cc_t c_cc[19];          /* control characters */
+        speed_t c_ispeed;       /* input speed */
+        speed_t c_ospeed;       /* output speed */
+    } tio2;
+    if (::ioctl(handle, TCGETS2, &tio2) != -1) {
+        // If it's already in low latency, no further configuration is necessary
+        if (!(tio2.c_cflag & ASYNC_LOW_LATENCY)) {
+            tio2.c_cflag |= ASYNC_LOW_LATENCY;
+            ::ioctl(handle, TCSETS2, &tio2);
+        } else {
+            qDebug() << "Low latency mode is already in termios2.";
+        }
+    } else {
+        qWarning() << "Failed to get termios2 struct from system.";
+    }
+
+    // Check again same configuration with serial_struct
+    serial_struct serial;
+    ::memset(&serial, 0, sizeof(serial));
+    if (::ioctl(handle, TIOCGSERIAL, &serial) == -1) {
+        qWarning() << "Failed to get serial_struct from system.";
+        return false;
+    }
+
+    // If it's already in low latency, no further configuration is necessary
+    if (serial.flags & ASYNC_LOW_LATENCY) {
+        qDebug() << "Low latency mode is already in serial_struct.";
+        return true;
+    }
+
+    // It's not possible to check for errors since the driver may not support it
+    serial.flags |= ASYNC_LOW_LATENCY;
+    ::ioctl(handle, TIOCSSERIAL, &serial);
+
+    //light at the end of the tunnel
+    return true;
+}
 ComHandle::ComHandle(QSerialPortInfo p)
 {
     serialPort = new QSerialPort(p);
+    setLowLatency();
 }
 
 bool ComHandle::open()

diff --git a/com-handle.h b/com-handle.h
@@ -14,6 +14,7 @@ class ComHandle : public QObject
     void close();
 
     void write(uint8_t* data, uint16_t length);
+    bool setLowLatency();
 
     QSerialPort* serialPort;