Dshoot600 BLHELI_S 16.6 on AUX PINS wants throttle calibration

ArduPlane Plane 3.9
1

I upgraded my ESC to this one https://banggood.com/EXUAV-Lighting-70A-2-6S-BLHeli_S-Brushless-ESC-Support-Dshot600-for-RC-FPV-Racing-Drone-p-1246574.html

The ESC seems support Dshoot 600 so I moved throttle to SERVO9 (AUX PIN 1) and set SERVO_BLH_OTYPE to 6.

When I turn on safety switch and arm the motor sound like blheli classic pwm throttle range calibration process; when I raise up throttle the esc sound like pwm classic throttle range calibration process ending…

But as far as I understand, dshoot is digital and doesn’t require calibration…

Could you help me to find the problem please… ?
Pixhawk 2.4.8 with ChibiOS

2

After SERVO_BLH_MASK change to 256 to enable dshot on SERVO_9, the esc seems to work (no calibration starting on motor arming…); but the motor sound a little bit strange (timing or startup power problem or something else…) ?

How can I be sure that the ESC and the FC are communicating with dshot ?

Thanks