px4io: add FMU fail test mode

In order to test what happens in px4iofirmware when the FMU stops
sending PWM or control commands, I added a test mode. When the test mode
is activated, no controls are sent.

src/drivers/px4io/px4io.cpp

@@ -218,6 +218,16 @@ public:
 	 */
 	int			print_debug();
 
+	/*
+	 * To test what happens if IO stops receiving updates from FMU.
+	 *
+	 * @param is_fail	true for failure condition, false for normal operation.
+	 */
+	void			test_fmu_fail(bool is_fail)
+	{
+		_test_fmu_fail = is_fail;
+	};
+
 #ifdef CONFIG_ARCH_BOARD_PX4FMU_V1
 	/**
 	 * Set the DSM VCC is controlled by relay one flag
@@ -315,6 +325,7 @@ private:
 	float			_analog_rc_rssi_volt; ///< analog RSSI voltage
 
 	float			_last_throttle; ///< last throttle value for battery calculation
+	bool			_test_fmu_fail; ///< To test what happens if IO looses FMU
 
 #ifdef CONFIG_ARCH_BOARD_PX4FMU_V1
 	bool			_dsm_vcc_ctl;		///< true if relay 1 controls DSM satellite RX power
@@ -549,7 +560,8 @@ PX4IO::PX4IO(device::Device *interface) :
 	_rssi_pwm_min(0),
 	_analog_rc_rssi_stable(false),
 	_analog_rc_rssi_volt(-1.0f),
-	_last_throttle(0.0f)
+	_last_throttle(0.0f),
+	_test_fmu_fail(false)
 #ifdef CONFIG_ARCH_BOARD_PX4FMU_V1
 	, _dsm_vcc_ctl(false)
 #endif
@@ -1349,8 +1361,12 @@ PX4IO::io_set_control_state(unsigned group)
 		_last_throttle = controls.control[3];
 	}
 
-	/* copy values to registers in IO */
-	return io_reg_set(PX4IO_PAGE_CONTROLS, group * PX4IO_PROTOCOL_MAX_CONTROL_COUNT, regs, _max_controls);
+	if (!_test_fmu_fail) {
+		/* copy values to registers in IO */
+		return io_reg_set(PX4IO_PAGE_CONTROLS, group * PX4IO_PROTOCOL_MAX_CONTROL_COUNT, regs, _max_controls);
+	} else {
+		return OK;
+	}
 }
 
 
@@ -2735,8 +2751,14 @@ PX4IO::ioctl(file *filep, int cmd, unsigned long arg)
 				ret = -EINVAL;
 
 			} else {
-				/* send a direct PWM value */
-				ret = io_reg_set(PX4IO_PAGE_DIRECT_PWM, channel, arg);
+				if (!_test_fmu_fail) {
+					/* send a direct PWM value */
+					ret = io_reg_set(PX4IO_PAGE_DIRECT_PWM, channel, arg);
+				} else {
+					/* Just silently accept the ioctl without doing anything
+					 * in test mode. */
+					ret = OK;
+				}
 			}
 
 			break;
@@ -3037,7 +3059,12 @@ PX4IO::write(file * /*filp*/, const char *buffer, size_t len)
 	if (count > 0) {
 
 		perf_begin(_perf_write);
-		int ret = io_reg_set(PX4IO_PAGE_DIRECT_PWM, 0, (uint16_t *)buffer, count);
+
+		int ret = OK;
+		/* The write() is silently ignored in test mode. */
+		if (!_test_fmu_fail) {
+			ret = io_reg_set(PX4IO_PAGE_DIRECT_PWM, 0, (uint16_t *)buffer, count);
+		}
 		perf_end(_perf_write);
 
 		if (ret != OK) {
@@ -3869,8 +3896,29 @@ px4io_main(int argc, char *argv[])
 		exit(0);
 	}
 
+	if (!strcmp(argv[1], "test_fmu_fail")) {
+		if (g_dev != nullptr) {
+			g_dev->test_fmu_fail(true);
+			exit(0);
+		} else {
+
+			errx(1, "px4io must be started first");
+		}
+	}
+
+	if (!strcmp(argv[1], "test_fmu_ok")) {
+		if (g_dev != nullptr) {
+			g_dev->test_fmu_fail(false);
+			exit(0);
+		} else {
+
+			errx(1, "px4io must be started first");
+		}
+	}
+
 out:
 	errx(1, "need a command, try 'start', 'stop', 'status', 'test', 'monitor', 'debug <level>',\n"
 	     "'recovery', 'limit <rate>', 'current', 'bind', 'checkcrc', 'safety_on', 'safety_off',\n"
-	     "'forceupdate', 'update', 'sbus1_out', 'sbus2_out', 'rssi_analog' or 'rssi_pwm'");
+	     "'forceupdate', 'update', 'sbus1_out', 'sbus2_out', 'rssi_analog' or 'rssi_pwm',\n"
+	     "'test_fmu_fail', 'test_fmu_ok'");
 }