lidar.connect() does not clear DTR and motor will stop

[fdoljack]

Testing on the A1M8 which is not set up for variable motor speed using the Slamtec USB adapter board I found that this initiating command leaves the CTRL_MOT line low, after which the motor comes to a stop. This line is actually DTR on the UART. Most example code for scanning immediately implements "lidar.set_motor_pwm(500)", which in turn clears DTR and the motor continues to run. I found that sending other commands did not fix this and only the set_motor_pwm() command corrected the state of DTR. Failure to use the set_motor_pwm() command after the connect() command will cause scans to fail. The use of no other command fixes DTR and it remains low. In the Slamtec C++ SDK in net_serial.cpp these lines of code are found which addresses the point.

//Clear the DTR bit to let the motor spin
clearDTR();

To demonstrate the issue here one can use the following test code but with a time delay.

from pyrplidar import PyRPlidar
import time

lidar = PyRPlidar()
lidar.connect(port="/dev/ttyUSB0", baudrate=115200, timeout=3)

info = lidar.get_info()
print("info :", info)

health = lidar.get_health()
print("health :", health)

samplerate = lidar.get_samplerate()
print("samplerate :", samplerate)

scan_modes = lidar.get_scan_modes()
print("scan modes :")
for scan_mode in scan_modes:
print(scan_mode)

time.sleep(6.0)

#now watch the motor come to a stop
#after disconnect() the motor starts again

lidar.disconnect()