I would like to write a hardware_interface driver for the PCA9685 PWM shield. This chip is used to generate up to 12 PWM signals to drive servo motors or other devices which can be controlled via PWM.

The shield does not provide any feedback from the continuous servo motors. When I command a velocity via a pwm signal, I can only assume the servos are executing the command properly. Position-wise, I get no information about the current servo state.

For now, I am interested in controlling 4 servo motors (of a skid-steered robot). Is it possible to write a hardwareinterface which is compatible with ros2controllers, in particular with the diffdrivecontroller without exporting any stateinterfaces?