Modules Reference: Optical Flow (Driver) 
thoneflow 
Source: drivers/optical_flow/thoneflow
Description 
Serial bus driver for the ThoneFlow-3901U optical flow sensor.
Most boards are configured to enable/start the driver on a specified UART using the SENS_TFLOW_CFG parameter.
Setup/usage information: https://docs.px4.io/v1.15/en/sensor/pmw3901.html#thone-thoneflow-3901u
Examples 
Attempt to start driver on a specified serial device.
thoneflow start -d /dev/ttyS1Stop driver
thoneflow stopUsage 
thoneflow <command> [arguments...]
 Commands:
   start         Start driver
     -d <val>    Serial device
   stop          Stop driver
   info          Print driver information