Revert "px4io: replace safety_off state with safety button event (#19558)"

This reverts commit 12a81979a8.

msg/px4io_status.msg

@@ -19,7 +19,7 @@ bool status_rc_ppm
 bool status_rc_sbus
 bool status_rc_st24
 bool status_rc_sumd
-bool status_safety_button_event # px4io safety button was pressed for longer than 1 second
+bool status_safety_off
 
 # PX4IO alarms (PX4IO_P_STATUS_ALARMS)
 bool alarm_pwm_error

src/drivers/drv_pwm_output.h

@@ -188,6 +188,12 @@ typedef uint16_t	servo_position_t;
 /** get the maximum PWM value the output will send */
 #define PWM_SERVO_GET_MAX_PWM	_PX4_IOC(_PWM_SERVO_BASE, 19)
 
+/** force safety switch off (to disable use of safety switch) */
+#define PWM_SERVO_SET_FORCE_SAFETY_OFF		_PX4_IOC(_PWM_SERVO_BASE, 25)
+
+/** force safety switch on (to enable use of safety switch) */
+#define PWM_SERVO_SET_FORCE_SAFETY_ON		_PX4_IOC(_PWM_SERVO_BASE, 28)
+
 /*
  *
  *

src/drivers/pca9685_pwm_out/main.cpp

@@ -492,7 +492,9 @@ int PCA9685Wrapper::ioctl(cdev::file_t *filep, int cmd, unsigned long arg)
 		break;
 
 	case PWM_SERVO_SET_ARM_OK:
+	case PWM_SERVO_SET_FORCE_SAFETY_OFF:
 	case PWM_SERVO_CLEAR_ARM_OK:
+	case PWM_SERVO_SET_FORCE_SAFETY_ON:
 	case PWM_SERVO_ARM:
 	case PWM_SERVO_DISARM:
 		break;

src/drivers/pwm_out/PWMOut.cpp

@@ -717,6 +717,8 @@ int PWMOut::pwm_ioctl(device::file_t *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:
+	case PWM_SERVO_SET_FORCE_SAFETY_ON:
 		break;
 
 	case PWM_SERVO_DISARM:

src/drivers/px4io/px4io.cpp

@@ -74,7 +74,6 @@
 #include <uORB/topics/input_rc.h>
 #include <uORB/topics/vehicle_command.h>
 #include <uORB/topics/vehicle_command_ack.h>
-#include <uORB/topics/vehicle_status.h>
 #include <uORB/topics/px4io_status.h>
 #include <uORB/topics/parameter_update.h>
 
@@ -197,8 +196,7 @@ private:
 	uint16_t		_last_written_arming_c{0};	///< the last written arming state reg
 
 	uORB::Subscription	_t_actuator_armed{ORB_ID(actuator_armed)};		///< system armed control topic
-	uORB::Subscription	_t_vehicle_command{ORB_ID(vehicle_command)};	///< vehicle command topic
-	uORB::Subscription	_t_vehicle_status{ORB_ID(vehicle_status)};		///< vehicle status topic
+	uORB::Subscription	_t_vehicle_command{ORB_ID(vehicle_command)};		///< vehicle command topic
 
 	uORB::SubscriptionInterval _parameter_update_sub{ORB_ID(parameter_update), 1_s};
 
@@ -445,14 +443,15 @@ int PX4IO::init()
 		// the startup script to be able to load a new IO
 		// firmware
 
+		// If IO has already safety off it won't accept going into bootloader mode,
+		// therefore we need to set safety on first.
+		io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_FORCE_SAFETY_ON, PX4IO_FORCE_SAFETY_MAGIC);
+
 		// Now the reboot into bootloader mode should succeed.
 		io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_REBOOT_BL, PX4IO_REBOOT_BL_MAGIC);
 		return -1;
 	}
 
-	/* Set safety_off to false when FMU boot*/
-	io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_SAFETY_OFF, 0);
-
 	if (_max_rc_input > input_rc_s::RC_INPUT_MAX_CHANNELS) {
 		_max_rc_input = input_rc_s::RC_INPUT_MAX_CHANNELS;
 	}
@@ -477,6 +476,14 @@ int PX4IO::init()
 		return ret;
 	}
 
+	/* set safety to off if circuit breaker enabled */
+	if (circuit_breaker_enabled("CBRK_IO_SAFETY", CBRK_IO_SAFETY_KEY)) {
+		io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_FORCE_SAFETY_OFF, PX4IO_FORCE_SAFETY_MAGIC);
+
+	} else {
+		io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_FORCE_SAFETY_ON, PX4IO_FORCE_SAFETY_MAGIC);
+	}
+
 	/* try to claim the generic PWM output device node as well - it's OK if we fail at this */
 	if (_param_sys_hitl.get() <= 0 && _param_sys_use_io.get() == 1) {
 		_class_instance = register_class_devname(PWM_OUTPUT_BASE_DEVICE_PATH);
@@ -614,6 +621,11 @@ void PX4IO::Run()
 
 			update_params();
 
+			/* Check if the IO safety circuit breaker has been updated */
+			bool circuit_breaker_io_safety_enabled = circuit_breaker_enabled("CBRK_IO_SAFETY", CBRK_IO_SAFETY_KEY);
+			/* Bypass IO safety switch logic by setting FORCE_SAFETY_OFF */
+			io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_FORCE_SAFETY_OFF, circuit_breaker_io_safety_enabled);
+
 			/* Check if the flight termination circuit breaker has been updated */
 			bool disable_flighttermination = circuit_breaker_enabled("CBRK_FLIGHTTERM", CBRK_FLIGHTTERM_KEY);
 			/* Tell IO that it can terminate the flight if FMU is not responding or if a failure has been reported by the FailureDetector logic */
@@ -962,12 +974,15 @@ int PX4IO::io_handle_status(uint16_t status)
 	 */
 
 	/* check for IO reset - force it back to armed if necessary */
-	if (!(status & PX4IO_P_STATUS_FLAGS_ARM_SYNC)) {
+	if (_status & PX4IO_P_STATUS_FLAGS_SAFETY_OFF && !(status & PX4IO_P_STATUS_FLAGS_SAFETY_OFF)
+	    && !(status & PX4IO_P_STATUS_FLAGS_ARM_SYNC)) {
 		/* set the arming flag */
-		ret = io_reg_modify(PX4IO_PAGE_STATUS, PX4IO_P_STATUS_FLAGS, 0, PX4IO_P_STATUS_FLAGS_ARM_SYNC);
+		ret = io_reg_modify(PX4IO_PAGE_STATUS, PX4IO_P_STATUS_FLAGS, 0,
+				    PX4IO_P_STATUS_FLAGS_SAFETY_OFF | PX4IO_P_STATUS_FLAGS_ARM_SYNC);
 
 		/* set new status */
 		_status = status;
+		_status &= PX4IO_P_STATUS_FLAGS_SAFETY_OFF;
 
 	} else if (!(_status & PX4IO_P_STATUS_FLAGS_ARM_SYNC)) {
 
@@ -984,26 +999,18 @@ int PX4IO::io_handle_status(uint16_t status)
 	}
 
 	/**
-	 * Get and handle the safety button status
+	 * Get and handle the safety status
 	 */
-	const bool safety_button_pressed = status & PX4IO_P_STATUS_FLAGS_SAFETY_BUTTON_EVENT;
+	const bool safety_off = status & PX4IO_P_STATUS_FLAGS_SAFETY_OFF;
 
-	if (safety_button_pressed) {
-		io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_SAFETY_BUTTON_ACK, 0);
+	/* px4io board will change safety_off from false to true and stay like that until the vehicle is rebooted
+	 * where safety will change back to false. Here we are triggering the safety button event once.
+	 * TODO: change px4io firmware to act on the event. This will enable the "force safety on disarming" feature. */
+	if (_previous_safety_off != safety_off) {
 		_button_publisher.safetyButtonTriggerEvent();
 	}
 
-	/**
-	 * Inform PX4IO board about safety_off state for LED control
-	 */
-	vehicle_status_s vehicle_status;
-
-	if (_t_vehicle_status.update(&vehicle_status)) {
-		if (_previous_safety_off != vehicle_status.safety_off) {
-			io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_SAFETY_OFF, vehicle_status.safety_off);
-			_previous_safety_off = vehicle_status.safety_off;
-		}
-	}
+	_previous_safety_off = safety_off;
 
 	return ret;
 }
@@ -1026,17 +1033,37 @@ int PX4IO::dsm_bind_ioctl(int dsmMode)
 		return -EINVAL;
 	}
 
+	// Check if safety was off
+	bool safety_off = (_status & PX4IO_P_STATUS_FLAGS_SAFETY_OFF);
+	int ret = -1;
+
+	// Put safety on
+	if (safety_off) {
+		// re-enable safety
+		ret = io_reg_modify(PX4IO_PAGE_STATUS, PX4IO_P_STATUS_FLAGS, PX4IO_P_STATUS_FLAGS_SAFETY_OFF, 0);
+
+		// set new status
+		_status &= ~(PX4IO_P_STATUS_FLAGS_SAFETY_OFF);
+	}
+
 	PX4_INFO("Binding DSM%s RX", (dsmMode == DSM2_BIND_PULSES) ? "2" : ((dsmMode == DSMX_BIND_PULSES) ? "-X" : "-X8"));
 
-	int ret = OK;
-	ret |= io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_DSM, dsm_bind_power_down);
+	io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_DSM, dsm_bind_power_down);
 	px4_usleep(500000);
-	ret |= io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_DSM, dsm_bind_set_rx_out);
-	ret |= io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_DSM, dsm_bind_power_up);
+	io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_DSM, dsm_bind_set_rx_out);
+	io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_DSM, dsm_bind_power_up);
 	px4_usleep(72000);
-	ret |= io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_DSM, dsm_bind_send_pulses | (dsmMode << 4));
+	io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_DSM, dsm_bind_send_pulses | (dsmMode << 4));
 	px4_usleep(50000);
-	ret |= io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_DSM, dsm_bind_reinit_uart);
+	io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_DSM, dsm_bind_reinit_uart);
+	ret = OK;
+
+	// Put safety back off
+	if (safety_off) {
+		ret = io_reg_modify(PX4IO_PAGE_STATUS, PX4IO_P_STATUS_FLAGS, 0,
+				    PX4IO_P_STATUS_FLAGS_SAFETY_OFF);
+		_status |= PX4IO_P_STATUS_FLAGS_SAFETY_OFF;
+	}
 
 	if (ret != OK) {
 		PX4_INFO("Binding DSM failed");
@@ -1106,7 +1133,7 @@ int PX4IO::io_get_status()
 		status.status_arm_sync        = STATUS_FLAGS & PX4IO_P_STATUS_FLAGS_ARM_SYNC;
 		status.status_init_ok         = STATUS_FLAGS & PX4IO_P_STATUS_FLAGS_INIT_OK;
 		status.status_failsafe        = STATUS_FLAGS & PX4IO_P_STATUS_FLAGS_FAILSAFE;
-		status.status_safety_button_event = STATUS_FLAGS & PX4IO_P_STATUS_FLAGS_SAFETY_BUTTON_EVENT;
+		status.status_safety_off      = STATUS_FLAGS & PX4IO_P_STATUS_FLAGS_SAFETY_OFF;
 
 		// PX4IO_P_STATUS_ALARMS
 		status.alarm_rc_lost       = STATUS_ALARMS & PX4IO_P_STATUS_ALARMS_RC_LOST;
@@ -1617,6 +1644,18 @@ int PX4IO::ioctl(file *filep, int cmd, unsigned long arg)
 		*(unsigned *)arg = _max_actuators;
 		break;
 
+	case PWM_SERVO_SET_FORCE_SAFETY_OFF:
+		PX4_DEBUG("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 PWM_SERVO_SET_FORCE_SAFETY_ON:
+		PX4_DEBUG("PWM_SERVO_SET_FORCE_SAFETY_ON");
+		/* force safety switch on */
+		ret = io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_FORCE_SAFETY_ON, PX4IO_FORCE_SAFETY_MAGIC);
+		break;
+
 	case DSM_BIND_START:
 		/* bind a DSM receiver */
 		ret = dsm_bind_ioctl(arg);
@@ -1686,6 +1725,16 @@ int PX4IO::ioctl(file *filep, int cmd, unsigned long arg)
 
 		}
 
+		// re-enable safety
+		ret = io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_FORCE_SAFETY_ON, PX4IO_FORCE_SAFETY_MAGIC);
+
+		if (ret != PX4_OK) {
+			PX4_WARN("IO refused to re-enable safety");
+		}
+
+		// set new status
+		_status &= ~(PX4IO_P_STATUS_FLAGS_SAFETY_OFF);
+
 		/* reboot into bootloader - arg must be PX4IO_REBOOT_BL_MAGIC */
 		usleep(1);
 		ret = io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_REBOOT_BL, arg);
@@ -2009,6 +2058,29 @@ int PX4IO::custom_command(int argc, char *argv[])
 		return 1;
 	}
 
+
+	if (!strcmp(verb, "safety_off")) {
+		int ret = get_instance()->ioctl(NULL, PWM_SERVO_SET_FORCE_SAFETY_OFF, 0);
+
+		if (ret != OK) {
+			PX4_ERR("failed to disable safety (%i)", ret);
+			return 1;
+		}
+
+		return 0;
+	}
+
+	if (!strcmp(verb, "safety_on")) {
+		int ret = get_instance()->ioctl(NULL, PWM_SERVO_SET_FORCE_SAFETY_ON, 0);
+
+		if (ret != OK) {
+			PX4_ERR("failed to enable safety (%i)", ret);
+			return 1;
+		}
+
+		return 0;
+	}
+
 	if (!strcmp(verb, "debug")) {
 		if (argc <= 1) {
 			PX4_ERR("usage: px4io debug LEVEL");
@@ -2090,6 +2162,8 @@ Output driver communicating with the IO co-processor.
 	PRINT_MODULE_USAGE_ARG("<filename>", "Firmware file", false);
 	PRINT_MODULE_USAGE_COMMAND_DESCR("update", "Update IO firmware");
 	PRINT_MODULE_USAGE_ARG("<filename>", "Firmware file", true);
+	PRINT_MODULE_USAGE_COMMAND_DESCR("safety_off", "Turn off safety (force)");
+	PRINT_MODULE_USAGE_COMMAND_DESCR("safety_on", "Turn on safety (force)");
 	PRINT_MODULE_USAGE_COMMAND_DESCR("debug", "set IO debug level");
 	PRINT_MODULE_USAGE_ARG("<debug_level>", "0=disabled, 9=max verbosity", false);
 	PRINT_MODULE_USAGE_COMMAND_DESCR("bind", "DSM bind");

src/drivers/uavcan/uavcan_main.cpp

@@ -951,6 +951,8 @@ UavcanNode::ioctl(file *filp, int cmd, unsigned long arg)
 	switch (cmd) {
 	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;
 
 	case MIXERIOCRESET:

src/modules/commander/commander_params.c

@@ -927,7 +927,7 @@ PARAM_DEFINE_INT32(COM_PREARM_MODE, 0);
 /**
  * Enable force safety
  *
- * Force safety when the vehicle disarms
+ * Force safety when the vehicle disarms. Not supported when safety button used over PX4IO board.
  *
  * @boolean
  * @group Commander

src/modules/commander/esc_calibration.cpp

@@ -187,6 +187,13 @@ static int do_esc_calibration_ioctl(orb_advert_t *mavlink_log_pub)
 		goto Out;
 	}
 
+	/* tell IO to switch off safety without using the safety switch */
+	if (px4_ioctl(fd, PWM_SERVO_SET_FORCE_SAFETY_OFF, 0) != PX4_OK) {
+		calibration_log_critical(mavlink_log_pub, CAL_QGC_FAILED_MSG, "Unable to force safety off");
+		return_code = PX4_ERROR;
+		goto Out;
+	}
+
 	calibration_log_info(mavlink_log_pub, "[cal] Connect battery now");
 
 	timeout_start = hrt_absolute_time();
@@ -226,6 +233,9 @@ static int do_esc_calibration_ioctl(orb_advert_t *mavlink_log_pub)
 Out:
 
 	if (fd != -1) {
+		if (px4_ioctl(fd, PWM_SERVO_SET_FORCE_SAFETY_ON, 0) != PX4_OK) {
+			calibration_log_info(mavlink_log_pub, CAL_QGC_FAILED_MSG, "Safety switch still off");
+		}
 
 		if (px4_ioctl(fd, PWM_SERVO_DISARM, 0) != PX4_OK) {
 			calibration_log_info(mavlink_log_pub, CAL_QGC_FAILED_MSG, "Servos still armed");

src/modules/px4iofirmware/CMakeLists.txt

@@ -39,7 +39,7 @@ add_library(px4iofirmware
 	mixer.cpp
 	px4io.cpp
 	registers.c
-	safety_button.cpp
+	safety.cpp
 	serial.cpp
 )
 

src/modules/px4iofirmware/mixer.cpp

@@ -134,11 +134,13 @@ mixer_tick()
 	 * FMU or from the mixer.
 	 *
 	 */
-	should_arm = (r_status_flags & PX4IO_P_STATUS_FLAGS_INIT_OK)		/* IO initialised without error */
+	should_arm = (r_status_flags & PX4IO_P_STATUS_FLAGS_INIT_OK)				/* IO initialised without error */
+		     && (r_status_flags & PX4IO_P_STATUS_FLAGS_SAFETY_OFF)			/* and IO is armed */
 		     && (r_setup_arming & PX4IO_P_SETUP_ARMING_FMU_ARMED)		/* and FMU is armed */
 		     ;
 
-	should_arm_nothrottle = ((r_status_flags & PX4IO_P_STATUS_FLAGS_INIT_OK)  /* IO initialised without error */
+	should_arm_nothrottle = ((r_status_flags & PX4IO_P_STATUS_FLAGS_INIT_OK)              /* IO initialised without error */
+				 && (r_status_flags & PX4IO_P_STATUS_FLAGS_SAFETY_OFF)        /* and IO is armed */
 				 && ((r_setup_arming & PX4IO_P_SETUP_ARMING_FMU_PREARMED)     /* and FMU is prearmed */
 				     || (r_status_flags & PX4IO_P_STATUS_FLAGS_RAW_PWM)       /* or direct PWM is set */
 				    ));

src/modules/px4iofirmware/protocol.h

@@ -1,6 +1,6 @@
 /****************************************************************************
  *
- *   Copyright (c) 2012-2022 PX4 Development Team. All rights reserved.
+ *   Copyright (c) 2012-2017 PX4 Development Team. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -114,7 +114,6 @@
 #define PX4IO_P_STATUS_FLAGS_FMU_INITIALIZED	(1 << 11) /* FMU was initialized and OK once */
 #define PX4IO_P_STATUS_FLAGS_RC_ST24		(1 << 12) /* ST24 input is valid */
 #define PX4IO_P_STATUS_FLAGS_RC_SUMD		(1 << 13) /* SUMD input is valid */
-#define PX4IO_P_STATUS_FLAGS_SAFETY_BUTTON_EVENT	(1 << 14) /* px4io safety button was pressed for longer than 1 second */
 
 #define PX4IO_P_STATUS_ALARMS			3	 /* alarm flags - alarms latch, write 1 to a bit to clear it */
 #define PX4IO_P_STATUS_ALARMS_RC_LOST           (1 << 0) /* timed out waiting for RC input */
@@ -185,8 +184,12 @@ enum {							/* DSM bind states */
 
 #define PX4IO_P_SETUP_CRC			11	/* get CRC of IO firmware */
 /* storage space of 12 occupied by CRC */
-#define PX4IO_P_SETUP_SAFETY_BUTTON_ACK	14	/**< ACK from FMU when it gets safety button pressed status */
-#define PX4IO_P_SETUP_SAFETY_OFF		15	/**< FMU inform PX4IO about safety_off for LED indication*/
+#define PX4IO_P_SETUP_FORCE_SAFETY_OFF		12	/* force safety switch into
+                                                           'armed' (PWM enabled) state - this is a non-data write and
+                                                           hence index 12 can safely be used. */
+
+#define PX4IO_P_SETUP_FORCE_SAFETY_ON		14	/* force safety switch into 'disarmed' (PWM disabled state) */
+#define PX4IO_FORCE_SAFETY_MAGIC		22027	/* required argument for force safety (random) */
 #define PX4IO_P_SETUP_SBUS_RATE			16	/**< frame rate of SBUS1 output in Hz */
 #define PX4IO_P_SETUP_THERMAL			17	/**< thermal management */
 #define PX4IO_P_SETUP_ENABLE_FLIGHTTERMINATION	18	/**< flight termination; false if the circuit breaker (CBRK_FLIGHTTERM) is set */
@@ -209,7 +212,7 @@ enum {							/* DSM bind states */
 #define PX4IO_PAGE_TEST				127
 #define PX4IO_P_TEST_LED			0		/**< set the amber LED on/off */
 
-/* PWM disarmed values that are active */
+/* PWM disarmed values that are active, even when SAFETY_SAFE */
 #define PX4IO_PAGE_DISARMED_PWM			109		/* 0..CONFIG_ACTUATOR_COUNT-1 */
 
 /**

src/modules/px4iofirmware/px4io.cpp

@@ -154,7 +154,8 @@ show_debug_messages(void)
 static void
 update_mem_usage(void)
 {
-	if (/* FMU is armed */ (r_setup_arming & PX4IO_P_SETUP_ARMING_FMU_ARMED)) {
+	if (/* IO armed */ (r_status_flags & PX4IO_P_STATUS_FLAGS_SAFETY_OFF)
+			   /* and FMU is armed */ && (r_setup_arming & PX4IO_P_SETUP_ARMING_FMU_ARMED)) {
 		return;
 	}
 
@@ -182,7 +183,8 @@ ring_blink(void)
 {
 #if defined(LED_GREEN)
 
-	if (/* FMU is armed */ (r_setup_arming & PX4IO_P_SETUP_ARMING_FMU_ARMED)) {
+	if (/* IO armed */ (r_status_flags & PX4IO_P_STATUS_FLAGS_SAFETY_OFF)
+			   /* and FMU is armed */ && (r_setup_arming & PX4IO_P_SETUP_ARMING_FMU_ARMED)) {
 		LED_GREEN(true);
 		return;
 	}
@@ -312,8 +314,8 @@ extern "C" __EXPORT int user_start(int argc, char *argv[])
 	ENABLE_SBUS_OUT(false);
 #endif
 
-	/* start the safety button handler */
-	safety_button_init();
+	/* start the safety switch handler */
+	safety_init();
 
 	/* initialise the control inputs */
 	controls_init();

src/modules/px4iofirmware/px4io.h

@@ -131,6 +131,8 @@ extern struct sys_state_s system_state;
 # define ADC_VSERVO			4
 # define ADC_RSSI			5
 
+#define BUTTON_SAFETY		px4_arch_gpioread(GPIO_BTN_SAFETY)
+
 #define PX4_CRITICAL_SECTION(cmd)	{ irqstate_t flags = px4_enter_critical_section(); cmd; px4_leave_critical_section(flags); }
 
 void atomic_modify_or(volatile uint16_t *target, uint16_t modification);
@@ -143,9 +145,9 @@ void atomic_modify_and(volatile uint16_t *target, uint16_t modification);
 extern void	mixer_tick(void);
 
 /**
- * Safety button/LED.
+ * Safety switch/LED.
  */
-extern void	safety_button_init(void);
+extern void	safety_init(void);
 extern void	failsafe_led_init(void);
 
 /**

src/modules/px4iofirmware/registers.c

@@ -413,7 +413,7 @@ registers_set_one(uint8_t page, uint8_t offset, uint16_t value)
 			break;
 
 		case PX4IO_P_SETUP_REBOOT_BL:
-			if (r_status_flags & PX4IO_P_STATUS_FLAGS_OUTPUTS_ARMED) {
+			if (r_status_flags & PX4IO_P_STATUS_FLAGS_SAFETY_OFF) {
 				// don't allow reboot while armed
 				break;
 			}
@@ -433,19 +433,22 @@ registers_set_one(uint8_t page, uint8_t offset, uint16_t value)
 			dsm_bind(value & 0x0f, (value >> 4) & 0xF);
 			break;
 
-		case PX4IO_P_SETUP_SAFETY_BUTTON_ACK:
-			// clear safety button pressed flag so it can be used again
-			r_status_flags &= ~PX4IO_P_STATUS_FLAGS_SAFETY_BUTTON_EVENT;
+		case PX4IO_P_SETUP_FORCE_SAFETY_ON:
+			if (value == PX4IO_FORCE_SAFETY_MAGIC) {
+				r_status_flags &= ~PX4IO_P_STATUS_FLAGS_SAFETY_OFF;
+
+			} else {
+				return -1;
+			}
 
 			break;
 
-		case PX4IO_P_SETUP_SAFETY_OFF:
-
-			if (value) {
+		case PX4IO_P_SETUP_FORCE_SAFETY_OFF:
+			if (value == PX4IO_FORCE_SAFETY_MAGIC) {
 				r_status_flags |= PX4IO_P_STATUS_FLAGS_SAFETY_OFF;
 
 			} else {
-				r_status_flags &= ~PX4IO_P_STATUS_FLAGS_SAFETY_OFF;
+				return -1;
 			}
 
 			break;

src/modules/px4iofirmware/safety.cpp

@@ -32,7 +32,7 @@
  ****************************************************************************/
 
 /**
- * @file safety_button.cpp
+ * @file safety.cpp
  * Safety button logic.
  *
  * @author Lorenz Meier <lorenz@px4.io>
@@ -46,7 +46,7 @@
 
 #include "px4io.h"
 
-static struct hrt_call safety_button_call;
+static struct hrt_call arming_call;
 static struct hrt_call failsafe_call;
 
 /*
@@ -59,23 +59,30 @@ static unsigned counter = 0;
  * Define the various LED flash sequences for each system state.
  */
 #define LED_PATTERN_FMU_OK_TO_ARM		0x0003			/**< slow blinking			*/
-#define LED_PATTERN_FMU_REFUSE_TO_ARM	0x5555			/**< fast blinking			*/
+#define LED_PATTERN_FMU_REFUSE_TO_ARM		0x5555		/**< fast blinking			*/
 #define LED_PATTERN_IO_ARMED			0x5050			/**< long off, then double blink 	*/
 #define LED_PATTERN_FMU_ARMED			0x5500			/**< long off, then quad blink 		*/
 #define LED_PATTERN_IO_FMU_ARMED		0xffff			/**< constantly on			*/
 
 static unsigned blink_counter = 0;
 
-#define SAFETY_SWITCH_THRESHOLD	10
+/*
+ * IMPORTANT: The arming state machine critically
+ * 	      depends on using the same threshold
+ *            for arming and disarming. Since disarming
+ *            is quite deadly for the system, a similar
+ *            length can be justified.
+ */
+#define ARM_COUNTER_THRESHOLD	10
 
-static void safety_button_check(void *arg);
+static void safety_check_button(void *arg);
 static void failsafe_blink(void *arg);
 
 void
-safety_button_init(void)
+safety_init(void)
 {
 	/* arrange for the button handler to be called at 10Hz */
-	hrt_call_every(&safety_button_call, 1000, 100000, safety_button_check, NULL);
+	hrt_call_every(&arming_call, 1000, 100000, safety_check_button, NULL);
 }
 
 void
@@ -86,20 +93,26 @@ failsafe_led_init(void)
 }
 
 static void
-safety_button_check(void *arg)
+safety_check_button(void *arg)
 {
-	const bool safety_button_pressed = px4_arch_gpioread(GPIO_BTN_SAFETY);
+	const bool safety_button_pressed = BUTTON_SAFETY;
 
-	/* Keep safety button pressed for one second to trigger safety button event.
-	 * The logic to prevent turning on safety again is in the commander.
+	/* Keep safety button pressed for one second to turn off safety
+	 *
+	 * Note that safety cannot be turned on again by button because a button
+	 * hardware problem could accidentally disable it in flight.
 	 */
+	if (safety_button_pressed && !(r_status_flags & PX4IO_P_STATUS_FLAGS_SAFETY_OFF) &&
+	    (r_setup_arming & PX4IO_P_SETUP_ARMING_IO_ARM_OK)) {
 
-	if (safety_button_pressed && !(r_status_flags & PX4IO_P_STATUS_FLAGS_SAFETY_BUTTON_EVENT)) {
+		if (counter <= ARM_COUNTER_THRESHOLD) {
+			counter++;
 
-		counter++;
+		}
 
-		if (counter >= SAFETY_SWITCH_THRESHOLD) {
-			atomic_modify_or(&r_status_flags, PX4IO_P_STATUS_FLAGS_SAFETY_BUTTON_EVENT);
+		if (counter == ARM_COUNTER_THRESHOLD) {
+			// switch safety off -> ready to arm state
+			atomic_modify_or(&r_status_flags, PX4IO_P_STATUS_FLAGS_SAFETY_OFF);
 		}
 
 	} else {