hmc5883: much faster calibration code with bug fixes

this fixes two bugs in "hmc5883 calibrate" and also makes it much
faster, so it can be run on every boot. It now uses the correct 2.5Ga
range when calibrating, and fixes the expected values for X/Y/Z axes

The basic calibration approach is similar to the APM2 driver, waiting
for 10 good samples after discarding some initial samples. That allows
the calibration to run fast enough that it can be done on every boot
without causing too much boot delay.

src/drivers/hmc5883/hmc5883.cpp

@@ -849,41 +849,23 @@ HMC5883::collect()
 
 	/* scale values for output */
 
-	/*
-	 * 1) Scale raw value to SI units using scaling from datasheet.
-	 * 2) Subtract static offset (in SI units)
-	 * 3) Scale the statically calibrated values with a linear
-	 *    dynamically obtained factor
-	 *
-	 * Note: the static sensor offset is the number the sensor outputs
-	 * 	 at a nominally 'zero' input. Therefore the offset has to
-	 * 	 be subtracted.
-	 *
-	 *	 Example: A gyro outputs a value of 74 at zero angular rate
-	 *	 	  the offset is 74 from the origin and subtracting
-	 *		  74 from all measurements centers them around zero.
-	 */
-
 #ifdef PX4_I2C_BUS_ONBOARD
 	if (_bus == PX4_I2C_BUS_ONBOARD) {
-		/* to align the sensor axes with the board, x and y need to be flipped */
+		// convert onboard so it matches offboard for the
-		new_report.x = ((report.y * _range_scale) - _scale.x_offset) * _scale.x_scale;
+		// scaling below
-		/* flip axes and negate value for y */
+		report.y = -report.y;
-		new_report.y = ((-report.x * _range_scale) - _scale.y_offset) * _scale.y_scale;
+		report.x = -report.x;
-		/* z remains z */
+        }
-		new_report.z = ((report.z * _range_scale) - _scale.z_offset) * _scale.z_scale;
-	} else {
 #endif
-		/* the standard external mag by 3DR has x pointing to the right, y pointing backwards, and z down,
+
-		 * therefore switch x and y and invert y */
+	/* the standard external mag by 3DR has x pointing to the
+	 * right, y pointing backwards, and z down, therefore switch x
+	 * and y and invert y */
 	new_report.x = ((-report.y * _range_scale) - _scale.x_offset) * _scale.x_scale;
 	/* flip axes and negate value for y */
 	new_report.y = ((report.x * _range_scale) - _scale.y_offset) * _scale.y_scale;
 	/* z remains z */
 	new_report.z = ((report.z * _range_scale) - _scale.z_offset) * _scale.z_scale;
-#ifdef PX4_I2C_BUS_ONBOARD
-	}
-#endif
 
 	if (_mag_topic != -1) {
 		/* publish it */
@@ -910,6 +892,7 @@ int HMC5883::calibrate(struct file *filp, unsigned enable)
 	struct mag_report report;
 	ssize_t sz;
 	int ret = 1;
+	uint8_t good_count = 0;
 
 	// XXX do something smarter here
 	int fd = (int)enable;
@@ -932,32 +915,17 @@ int HMC5883::calibrate(struct file *filp, unsigned enable)
 		1.0f,
 	};
 
-	float avg_excited[3] = {0.0f, 0.0f, 0.0f};
+	float sum_excited[3] = {0.0f, 0.0f, 0.0f};
-	unsigned i;
+
+	/* expected axis scaling. The datasheet says that 766 will
+	 * be places in the X and Y axes and 713 in the Z
+	 * axis. Experiments show that in fact 766 is placed in X,
+	 * and 713 in Y and Z. This is relative to a base of 660
+	 * LSM/Ga, giving 1.16 and 1.08 */
+	float expected_cal[3] = { 1.16f, 1.08f, 1.08f };
 
 	warnx("starting mag scale calibration");
 
-	/* do a simple demand read */
-	sz = read(filp, (char *)&report, sizeof(report));
-
-	if (sz != sizeof(report)) {
-		warn("immediate read failed");
-		ret = 1;
-		goto out;
-	}
-
-	warnx("current measurement: %.6f  %.6f  %.6f", (double)report.x, (double)report.y, (double)report.z);
-	warnx("time:        %lld", report.timestamp);
-	warnx("sampling 500 samples for scaling offset");
-
-	/* set the queue depth to 10 */
-	/* don't do this for now, it can lead to a crash in start() respectively work_queue() */
-//	if (OK != ioctl(filp, SENSORIOCSQUEUEDEPTH, 10)) {
-//		warn("failed to set queue depth");
-//		ret = 1;
-//		goto out;
-//	}
-
 	/* start the sensor polling at 50 Hz */
 	if (OK != ioctl(filp, SENSORIOCSPOLLRATE, 50)) {
 		warn("failed to set 2Hz poll rate");
@@ -965,8 +933,9 @@ int HMC5883::calibrate(struct file *filp, unsigned enable)
 		goto out;
 	}
 
-	/* Set to 2.5 Gauss */
+	/* Set to 2.5 Gauss. We ask for 3 to get the right part of
-	if (OK != ioctl(filp, MAGIOCSRANGE, 2)) {
+         * the chained if statement above. */
+	if (OK != ioctl(filp, MAGIOCSRANGE, 3)) {
 		warnx("failed to set 2.5 Ga range");
 		ret = 1;
 		goto out;
@@ -990,8 +959,8 @@ int HMC5883::calibrate(struct file *filp, unsigned enable)
 		goto out;
 	}
 
-	/* read the sensor 10x and report each value */
+	// discard 10 samples to let the sensor settle
-	for (i = 0; i < 500; i++) {
+	for (uint8_t i = 0; i < 10; i++) {
 		struct pollfd fds;
 
 		/* wait for data to be ready */
@@ -1009,32 +978,69 @@ int HMC5883::calibrate(struct file *filp, unsigned enable)
 
 		if (sz != sizeof(report)) {
 			warn("periodic read failed");
+			ret = -EIO;
 			goto out;
+		}
+	}
 
-		} else {
+	/* read the sensor up to 50x, stopping when we have 10 good values */
-			avg_excited[0] += report.x;
+	for (uint8_t i = 0; i < 50 && good_count < 10; i++) {
-			avg_excited[1] += report.y;
+		struct pollfd fds;
-			avg_excited[2] += report.z;
+
+		/* wait for data to be ready */
+		fds.fd = fd;
+		fds.events = POLLIN;
+		ret = ::poll(&fds, 1, 2000);
+
+		if (ret != 1) {
+			warn("timed out waiting for sensor data");
+			goto out;
+		}
+
+		/* now go get it */
+		sz = ::read(fd, &report, sizeof(report));
+
+		if (sz != sizeof(report)) {
+			warn("periodic read failed");
+			ret = -EIO;
+			goto out;
+		}
+		float cal[3] = {fabsf(expected_cal[0] / report.x), 
+				fabsf(expected_cal[1] / report.y), 
+				fabsf(expected_cal[2] / report.z)};
+
+		if (cal[0] > 0.7f && cal[0] < 1.35f &&
+		    cal[1] > 0.7f && cal[1] < 1.35f &&
+		    cal[2] > 0.7f && cal[2] < 1.35f) {
+			good_count++;
+			sum_excited[0] += cal[0];
+			sum_excited[1] += cal[1];
+			sum_excited[2] += cal[2];
 		}
 
 		//warnx("periodic read %u", i);
 		//warnx("measurement: %.6f  %.6f  %.6f", (double)report.x, (double)report.y, (double)report.z);
+		//warnx("cal: %.6f  %.6f  %.6f", (double)cal[0], (double)cal[1], (double)cal[2]);
 	}
 
-	avg_excited[0] /= i;
+	if (good_count < 5) {
-	avg_excited[1] /= i;
+		warn("failed calibration");
-	avg_excited[2] /= i;
+		ret = -EIO;
+		goto out;
+	}
 
-	warnx("done. Performed %u reads", i);
+#if 0
-	warnx("measurement avg: %.6f  %.6f  %.6f", (double)avg_excited[0], (double)avg_excited[1], (double)avg_excited[2]);
+	warnx("measurement avg: %.6f  %.6f  %.6f", 
+	      (double)sum_excited[0]/good_count, 
+	      (double)sum_excited[1]/good_count, 
+	      (double)sum_excited[2]/good_count);
+#endif
 
 	float scaling[3];
 
-	/* calculate axis scaling */
+	scaling[0] = sum_excited[0] / good_count;
-	scaling[0] = fabsf(1.16f / avg_excited[0]);
+	scaling[1] = sum_excited[1] / good_count;
-	/* second axis inverted */
+	scaling[2] = sum_excited[2] / good_count;
-	scaling[1] = fabsf(1.16f / -avg_excited[1]);
-	scaling[2] = fabsf(1.08f / avg_excited[2]);
 
 	warnx("axes scaling: %.6f  %.6f  %.6f", (double)scaling[0], (double)scaling[1], (double)scaling[2]);
 
@@ -1165,6 +1171,8 @@ int HMC5883::set_excitement(unsigned enable)
 		conf_reg &= ~0x03;
 	}
 
+        // ::printf("set_excitement enable=%d regA=0x%x\n", (int)enable, (unsigned)conf_reg);
+
 	ret = write_reg(ADDR_CONF_A, conf_reg);
 
 	if (OK != ret)
@@ -1173,6 +1181,8 @@ int HMC5883::set_excitement(unsigned enable)
 	uint8_t conf_reg_ret;
 	read_reg(ADDR_CONF_A, conf_reg_ret);
 
+	//print_info();
+
 	return !(conf_reg == conf_reg_ret);
 }
 
@@ -1211,6 +1221,10 @@ HMC5883::print_info()
 	perf_print_counter(_comms_errors);
 	perf_print_counter(_buffer_overflows);
 	printf("poll interval:  %u ticks\n", _measure_ticks);
+	printf("offsets (%.2f %.2f %.2f)\n", (double)_scale.x_offset, (double)_scale.y_offset, (double)_scale.z_offset);
+	printf("scaling (%.2f %.2f %.2f) 1/range_scale %.2f range_ga %.2f\n", 
+	       (double)_scale.x_scale, (double)_scale.y_scale, (double)_scale.z_scale,
+	       (double)1.0/_range_scale, (double)_range_ga);
 	_reports->print_info("report queue");
 }