pwm: added PWM_SERVO_SET_FORCE_SAFETY_OFF ioctl

this allows the safety switch on px4io to be forced off

src/drivers/drv_pwm_output.h

@@ -199,6 +199,9 @@ ORB_DECLARE(output_pwm);
 /** get the lockdown override flag to enable outputs in HIL */
 #define PWM_SERVO_GET_DISABLE_LOCKDOWN		_IOC(_PWM_SERVO_BASE, 22)
 
+/** force safety switch off (to disable use of safety switch) */
+#define PWM_SERVO_SET_FORCE_SAFETY_OFF _IOC(_PWM_SERVO_BASE, 23)
+
 /*
  *
  *

src/drivers/px4fmu/fmu.cpp

@@ -736,6 +736,7 @@ PX4FMU::pwm_ioctl(file *filp, int cmd, unsigned long arg)
 
 	case PWM_SERVO_SET_ARM_OK:
 	case PWM_SERVO_CLEAR_ARM_OK:
+	case PWM_SERVO_SET_FORCE_SAFETY_OFF:
 		// these are no-ops, as no safety switch
 		break;
 

src/drivers/px4io/px4io.cpp

@@ -2129,6 +2129,10 @@ PX4IO::ioctl(file * filep, int cmd, unsigned long arg)
 
 	case PWM_SERVO_GET_DISABLE_LOCKDOWN:
 		*(unsigned *)arg = _lockdown_override;
+
+	case PWM_SERVO_SET_FORCE_SAFETY_OFF:
+		/* force safety swith off */
+		ret = io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_FORCE_SAFETY_OFF, PX4IO_FORCE_SAFETY_MAGIC);
 		break;
 
 	case DSM_BIND_START: