ll40ls: added reset and backoff logic to driver

this adds automatic resets of the lidar when it becomes unresponsive,
and also tries to cope with NACKs from long acquisition times. It also
adds a "ll40ls regdump" command, and fixes "ll40ls reset" to reset the
sensor.

The default acquisition period is changed to 50ms, with backoff to
100ms on a NACK

Note that there are still times when the sensor can get into an
unrecoverable state.

Thanks to Austin, Dennis and Bob from PulseLight for assistance in
tracking down the problems.

src/drivers/ll40ls/ll40ls.cpp

@@ -81,7 +81,9 @@
 /* LL40LS Registers addresses */
 
 #define LL40LS_MEASURE_REG		0x00		/* Measure range register */
+#define LL40LS_MSRREG_RESET	    0x00		/* reset to power on defaults */
 #define LL40LS_MSRREG_ACQUIRE	    0x04		/* Value to initiate a measurement, varies based on sensor revision */
+#define LL40LS_MAX_ACQ_COUNT_REG       0x02		/* maximum acquisition count register */
 #define LL40LS_DISTHIGH_REG		0x8F		/* High byte of distance register, auto increment */
 #define LL40LS_WHO_AM_I_REG         0x11
 #define LL40LS_WHO_AM_I_REG_VAL         0xCA
@@ -91,7 +93,11 @@
 #define LL40LS_MIN_DISTANCE (0.00f)
 #define LL40LS_MAX_DISTANCE (60.00f)
 
-#define LL40LS_CONVERSION_INTERVAL 100000 /* 100ms */
+// normal conversion wait time
+#define LL40LS_CONVERSION_INTERVAL 50*1000UL /* 50ms */
+
+// maximum time to wait for a conversion to complete.
+#define LL40LS_CONVERSION_TIMEOUT 100*1000UL /* 100ms */
 
 /* oddly, ERROR is not defined for c++ */
 #ifdef ERROR
@@ -119,6 +125,11 @@ public:
 	*/
 	void				print_info();
 
+	/**
+	 * print registers to console
+	 */
+	void					print_registers();
+
 protected:
 	virtual int			probe();
 	virtual int			read_reg(uint8_t reg, uint8_t &val);
@@ -138,7 +149,12 @@ private:
 	perf_counter_t		_sample_perf;
 	perf_counter_t		_comms_errors;
 	perf_counter_t		_buffer_overflows;
+	perf_counter_t		_sensor_resets;
+	perf_counter_t		_sensor_zero_resets;
 	uint16_t		_last_distance;
+	uint16_t		_zero_counter;
+	uint64_t		_acquire_time_usec;
+	volatile bool		_pause_measurements;
 
 	/**< the bus the device is connected to */
 	int			_bus;
@@ -182,6 +198,7 @@ private:
 	void				cycle();
 	int					measure();
 	int					collect();
+	int					reset_sensor();
 	/**
 	* Static trampoline from the workq context; because we don't have a
 	* generic workq wrapper yet.
@@ -211,7 +228,11 @@ LL40LS::LL40LS(int bus, const char *path, int address) :
 	_sample_perf(perf_alloc(PC_ELAPSED, "ll40ls_read")),
 	_comms_errors(perf_alloc(PC_COUNT, "ll40ls_comms_errors")),
 	_buffer_overflows(perf_alloc(PC_COUNT, "ll40ls_buffer_overflows")),
+	_sensor_resets(perf_alloc(PC_COUNT, "ll40ls_resets")),
+	_sensor_zero_resets(perf_alloc(PC_COUNT, "ll40ls_zero_resets")),
 	_last_distance(0),
+	_zero_counter(0),
+	_pause_measurements(false),
 	_bus(bus)
 {
 	// up the retries since the device misses the first measure attempts
@@ -242,6 +263,8 @@ LL40LS::~LL40LS()
 	perf_free(_sample_perf);
 	perf_free(_comms_errors);
 	perf_free(_buffer_overflows);
+	perf_free(_sensor_resets);
+	perf_free(_sensor_zero_resets);
 }
 
 int
@@ -298,26 +321,28 @@ LL40LS::probe()
 	_retries = 10;
 
 	for (uint8_t i=0; i<sizeof(addresses); i++) {
-		uint8_t val=0, who_am_i=0;
+		uint8_t who_am_i=0, max_acq_count=0;
 
 		// set the I2C bus address
 		set_address(addresses[i]);
 
-		if (read_reg(LL40LS_WHO_AM_I_REG, who_am_i) == OK && who_am_i == LL40LS_WHO_AM_I_REG_VAL) {
-			// it is responding correctly to a WHO_AM_I
+		/* register 2 defaults to 0x80. If this matches it is
+		   almost certainly a ll40ls */
+		if (read_reg(LL40LS_MAX_ACQ_COUNT_REG, max_acq_count) == OK && max_acq_count == 0x80) {
+			// very likely to be a ll40ls. This is the
+			// default max acquisition counter
 			goto ok;
 		}
 
-		if (read_reg(LL40LS_SIGNAL_STRENGTH_REG, val) == OK && val != 0) {
-			// very likely to be a ll40ls. px4flow does not
-			// respond to this
+		if (read_reg(LL40LS_WHO_AM_I_REG, who_am_i) == OK && who_am_i == LL40LS_WHO_AM_I_REG_VAL) {
+			// it is responding correctly to a
+			// WHO_AM_I. This works with older sensors (pre-production)
 			goto ok;
 		}
 
-		debug("WHO_AM_I byte mismatch 0x%02x should be 0x%02x val=0x%02x\n",
-		      (unsigned)who_am_i,
-		      LL40LS_WHO_AM_I_REG_VAL,
-		      (unsigned)val);
+		debug("probe failed reg11=0x%02x reg2=0x%02x\n",
+		      (unsigned)who_am_i, 
+		      (unsigned)max_acq_count);
 	}
 
 	// not found on any address
@@ -326,8 +351,9 @@ LL40LS::probe()
 ok:
 	_retries = 3;
 
-	// start a measurement
-	return measure();
+	// reset the sensor to ensure it is in a known state with
+	// correct settings
+	return reset_sensor();
 }
 
 void
@@ -447,8 +473,8 @@ LL40LS::ioctl(struct file *filp, int cmd, unsigned long arg)
 		return _reports->size();
 
 	case SENSORIOCRESET:
-		/* XXX implement this */
-		return -EINVAL;
+		reset_sensor();
+		return OK;
 
 	case RANGEFINDERIOCSETMINIUMDISTANCE: {
 			set_minimum_distance(*(float *)arg);
@@ -533,6 +559,13 @@ LL40LS::measure()
 {
 	int ret;
 
+	if (_pause_measurements) {
+		// we are in print_registers() and need to avoid
+		// acquisition to keep the I2C peripheral on the
+		// sensor active
+		return OK;
+	}
+
 	/*
 	 * Send the command to begin a measurement.
 	 */
@@ -541,15 +574,61 @@ LL40LS::measure()
 
 	if (OK != ret) {
 		perf_count(_comms_errors);
-		log("i2c::transfer returned %d", ret);
+		debug("i2c::transfer returned %d", ret);
+		// if we are getting lots of I2C transfer errors try
+		// resetting the sensor
+		if (perf_event_count(_comms_errors) % 10 == 0) {
+			perf_count(_sensor_resets);
+			reset_sensor();
+		}
 		return ret;
 	}
 
+	// remember when we sent the acquire so we can know when the
+	// acquisition has timed out
+	_acquire_time_usec = hrt_absolute_time();
 	ret = OK;
 
 	return ret;
 }
 
+/*
+  reset the sensor to power on defaults
+ */
+int
+LL40LS::reset_sensor()
+{
+	const uint8_t cmd[2] = { LL40LS_MEASURE_REG, LL40LS_MSRREG_RESET };
+	int ret = transfer(cmd, sizeof(cmd), nullptr, 0);
+	return ret;
+}
+
+/*
+  dump sensor registers for debugging
+ */
+void
+LL40LS::print_registers()
+{
+	_pause_measurements = true;
+	printf("ll40ls registers\n");
+	// wait for a while to ensure the lidar is in a ready state
+	usleep(50000);
+	for (uint8_t reg=0; reg<=0x67; reg++) {
+		uint8_t val = 0;
+		int ret = transfer(&reg, 1, &val, 1);
+		if (ret != OK) {
+			printf("%02x:XX ",(unsigned)reg);
+		} else {
+			printf("%02x:%02x ",(unsigned)reg, (unsigned)val);
+		}
+		if (reg % 16 == 15) {
+			printf("\n");
+		}
+	}
+	printf("\n");
+	_pause_measurements = false;
+}
+
 int
 LL40LS::collect()
 {
@@ -565,9 +644,22 @@ LL40LS::collect()
 	ret = transfer(&distance_reg, 1, &val[0], sizeof(val));
 
 	if (ret < 0) {
-		log("error reading from sensor: %d", ret);
-		perf_count(_comms_errors);
+		if (hrt_absolute_time() - _acquire_time_usec > LL40LS_CONVERSION_TIMEOUT) {
+			/*
+			  NACKs from the sensor are expected when we
+			  read before it is ready, so only consider it
+			  an error if more than 100ms has elapsed.
+			 */
+			debug("error reading from sensor: %d", ret);
+			perf_count(_comms_errors);
+			if (perf_event_count(_comms_errors) % 10 == 0) {
+				perf_count(_sensor_resets);
+				reset_sensor();
+			}
+		}
 		perf_end(_sample_perf);
+		// if we are getting lots of I2C transfer errors try
+		// resetting the sensor
 		return ret;
 	}
 
@@ -575,6 +667,25 @@ LL40LS::collect()
 	float si_units = distance * 0.01f; /* cm to m */
 	struct range_finder_report report;
 
+	if (distance == 0) {
+		_zero_counter++;
+		if (_zero_counter == 20) {
+			/* we have had 20 zeros in a row - reset the
+			   sensor. This is a known bad state of the
+			   sensor where it returns 16 bits of zero for
+			   the distance with a trailing NACK, and
+			   keeps doing that even when the target comes
+			   into a valid range.
+			*/
+			_zero_counter = 0;
+			perf_end(_sample_perf);
+			perf_count(_sensor_zero_resets);
+			return reset_sensor();
+		}
+	} else {
+		_zero_counter = 0;
+	}
+
 	_last_distance = distance;
 
 	/* this should be fairly close to the end of the measurement, so the best approximation of the time */
@@ -655,41 +766,47 @@ LL40LS::cycle()
 	/* collection phase? */
 	if (_collect_phase) {
 
-		/* perform collection */
+		/* try a collection */
 		if (OK != collect()) {
-			log("collection error");
-			/* restart the measurement state machine */
-			start();
-			return;
-		}
-
-		/* next phase is measurement */
-		_collect_phase = false;
-
-		/*
-		 * Is there a collect->measure gap?
-		 */
-		if (_measure_ticks > USEC2TICK(LL40LS_CONVERSION_INTERVAL)) {
-
-			/* schedule a fresh cycle call when we are ready to measure again */
-			work_queue(HPWORK,
-				   &_work,
-				   (worker_t)&LL40LS::cycle_trampoline,
-				   this,
-				   _measure_ticks - USEC2TICK(LL40LS_CONVERSION_INTERVAL));
-
-			return;
+			debug("collection error");
+			/* if we've been waiting more than 200ms then
+			   send a new acquire */
+			if (hrt_absolute_time() - _acquire_time_usec > LL40LS_CONVERSION_TIMEOUT*2) {
+				_collect_phase = false;
+			}
+		} else {
+			/* next phase is measurement */
+			_collect_phase = false;
+
+			/*
+			 * Is there a collect->measure gap?
+			 */
+			if (_measure_ticks > USEC2TICK(LL40LS_CONVERSION_INTERVAL)) {
+				
+				/* schedule a fresh cycle call when we are ready to measure again */
+				work_queue(HPWORK,
+					   &_work,
+					   (worker_t)&LL40LS::cycle_trampoline,
+					   this,
+					   _measure_ticks - USEC2TICK(LL40LS_CONVERSION_INTERVAL));
+				
+				return;
+			}
 		}
 	}
 
-	/* measurement phase */
-	if (OK != measure()) {
-		log("measure error");
+	if (_collect_phase == false) {
+		/* measurement phase */
+		if (OK != measure()) {
+			debug("measure error");
+		} else {
+			/* next phase is collection. Don't switch to
+			   collection phase until we have a successful
+			   acquire request I2C transfer */
+			_collect_phase = true;
+		}
 	}
 
-	/* next phase is collection */
-	_collect_phase = true;
-
 	/* schedule a fresh cycle call when the measurement is done */
 	work_queue(HPWORK,
 		   &_work,
@@ -704,6 +821,8 @@ LL40LS::print_info()
 	perf_print_counter(_sample_perf);
 	perf_print_counter(_comms_errors);
 	perf_print_counter(_buffer_overflows);
+	perf_print_counter(_sensor_resets);
+	perf_print_counter(_sensor_zero_resets);
 	printf("poll interval:  %u ticks\n", _measure_ticks);
 	_reports->print_info("report queue");
 	printf("distance: %ucm (0x%04x)\n",
@@ -730,6 +849,7 @@ void	stop(int bus);
 void	test(int bus);
 void	reset(int bus);
 void	info(int bus);
+void    regdump(int bus);
 void	usage();
 
 /**
@@ -939,10 +1059,27 @@ info(int bus)
 	exit(0);
 }
 
+/**
+ * Dump registers
+ */
+void
+regdump(int bus)
+{
+	LL40LS *g_dev = (bus == PX4_I2C_BUS_ONBOARD?g_dev_int:g_dev_ext);
+	if (g_dev == nullptr) {
+		errx(1, "driver not running");
+	}
+
+	printf("regdump @ %p\n", g_dev);
+	g_dev->print_registers();
+
+	exit(0);
+}
+
 void
 usage()
 {
-	warnx("missing command: try 'start', 'stop', 'info', 'test', 'reset', 'info'");
+	warnx("missing command: try 'start', 'stop', 'info', 'test', 'reset', 'info' or 'regdump'");
 	warnx("options:");
 	warnx("    -X only external bus");
 #ifdef PX4_I2C_BUS_ONBOARD
@@ -1004,6 +1141,13 @@ ll40ls_main(int argc, char *argv[])
 		ll40ls::reset(bus);
 	}
 
+	/*
+	 * dump registers
+	 */
+	if (!strcmp(verb, "regdump")) {
+		ll40ls::regdump(bus);
+	}
+
 	/*
 	 * Print driver information.
 	 */
@@ -1011,5 +1155,5 @@ ll40ls_main(int argc, char *argv[])
 		ll40ls::info(bus);
 	}
 
-	errx(1, "unrecognized command, try 'start', 'test', 'reset' or 'info'");
+	errx(1, "unrecognized command, try 'start', 'test', 'reset', 'info' or 'regdump'");
 }