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[Sample; do not merge] Use low latency mode by default in C++ dir. #516

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[Sample; do not merge] Use low latency mode by default in C++ dir. #516

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40 changes: 16 additions & 24 deletions c++/src/dynamixel_sdk/port_handler_linux.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -30,30 +30,7 @@

#include "port_handler_linux.h"

#define LATENCY_TIMER 16 // msec (USB latency timer)
// You should adjust the latency timer value. From the version Ubuntu 16.04.2, the default latency timer of the usb serial is '16 msec'.
// When you are going to use sync / bulk read, the latency timer should be loosen.
// the lower latency timer value, the faster communication speed.

// Note:
// You can check its value by:
// $ cat /sys/bus/usb-serial/devices/ttyUSB0/latency_timer
//
// If you think that the communication is too slow, type following after plugging the usb in to change the latency timer
//
// Method 1. Type following (you should do this everytime when the usb once was plugged out or the connection was dropped)
// $ echo 1 | sudo tee /sys/bus/usb-serial/devices/ttyUSB0/latency_timer
// $ cat /sys/bus/usb-serial/devices/ttyUSB0/latency_timer
//
// Method 2. If you want to set it as be done automatically, and don't want to do above everytime, make rules file in /etc/udev/rules.d/. For example,
// $ echo ACTION==\"add\", SUBSYSTEM==\"usb-serial\", DRIVER==\"ftdi_sio\", ATTR{latency_timer}=\"1\" > 99-dynamixelsdk-usb.rules
// $ sudo cp ./99-dynamixelsdk-usb.rules /etc/udev/rules.d/
// $ sudo udevadm control --reload-rules
// $ sudo udevadm trigger --action=add
// $ cat /sys/bus/usb-serial/devices/ttyUSB0/latency_timer
//
// or if you have another good idea that can be an alternatives,
// please give us advice via github issue https://github.com/ROBOTIS-GIT/DynamixelSDK/issues
#define LATENCY_TIMER 16 // now USB latency timer is always set to 1 on this application; the name should be renamed

struct termios2 {
tcflag_t c_iflag; /* input mode flags */
Expand Down Expand Up @@ -223,6 +200,21 @@ bool PortHandlerLinux::setupPort(int cflag_baud)
tcsetattr(socket_fd_, TCSANOW, &newtio);

tx_time_per_byte = (1000.0 / (double)baudrate_) * 10.0;

// set `/sys/bus/usb-serial/devices/{port_name_}/latency_timer` to 1 ms
struct serial_struct ss;
if(ioctl(socket_fd_, TIOCGSERIAL, &ss) != 0)
{
printf("[PortHandlerLinux::SetupPort] TIOCGSERIAL failed!\n");
return false;
}
ss.flags |= ASYNC_LOW_LATENCY;
if(ioctl(socket_fd_, TIOCSSERIAL, &ss) != 0)
{
printf("[PortHandlerLinux::SetupPort] TIOCSSERIAL failed!\n");
return false;
}

return true;
}

Expand Down