PX4 pixhawk AUX camera_trigger_params.c

Hello. I am newly working pixkhawk and trying to connect two cameras to pixhawk.

In ~px4_ws/Firmware/src/drivers/camera_trigger/camera_trigger_params.c, I have

PARAM_DEFINE_INT32(TRIG_INTERFACE, 4);
PARAM_DEFINE_FLOAT(TRIG_INTERVAL, 50.0f);
PARAM_DEFINE_INT32(TRIG_POLARITY, 0);
PARAM_DEFINE_FLOAT(TRIG_ACT_TIME, 50.0f);
PARAM_DEFINE_INT32(TRIG_MODE, 1);
PARAM_DEFINE_INT32(TRIG_PINS, 56);
PARAM_DEFINE_FLOAT(TRIG_DISTANCE, 25.0f);

and a couple of timestamps and frame numbers are (using rostopic echo /mavros/cam_imu_sync/cam_imu_stamp),

frame_stamp:
secs: 1497372502
nsecs: 671341616
frame_seq_id: 408

frame_stamp:
secs: 1497372502
nsecs: 721236896
frame_seq_id: 409

frame_stamp:
secs: 1497372502
nsecs: 771237896
frame_seq_id: 410

frame_stamp:
secs: 1497372502
nsecs: 820298912
frame_seq_id: 411

frame_stamp:
secs: 1497372502
nsecs: 870298912
frame_seq_id: 412

But I hooked up pin 5 and 6 to the scope and both channel showed 20ms (50 Hz) pulse trains. Thus, if the pulses are from trigger PWM, I should be able to echo a 100 Hz data. Am I correct?

Then, how can I actually control the interval of pwm signals?