sensor: akm09918c: Fix conversion constant

The sensor driver uses the value 500 to convert bit counts to microgauss
values, but it should actually be 1500. Edit the driver unit test to use
the macro instead of a magic number.

Signed-off-by: Tristan Honscheid <honscheid@google.com>

Author: tristan-google

drivers/sensor/akm09918c/akm09918c.h

@@ -7,6 +7,7 @@
 #define ZEPHYR_DRIVERS_SENSOR_AKM09918C_AKM09918C_H_
 
 #include <zephyr/device.h>
+#include <zephyr/drivers/i2c.h>
 #include <zephyr/drivers/sensor.h>
 
 #include "akm09918c_reg.h"
@@ -15,7 +16,17 @@
 #define AKM09918C_MEASURE_TIME_US 9000
 
 /* Conversion values */
-#define AKM09918C_MICRO_GAUSS_PER_BIT INT64_C(500)
+#define AKM09918C_MICRO_GAUSS_PER_BIT INT64_C(1500)
+
+/* Maximum and minimum raw register values for magnetometer data per datasheet */
+#define AKM09918C_MAGN_MAX_DATA_REG (32752)
+#define AKM09918C_MAGN_MIN_DATA_REG (-32752)
+
+/* Maximum and minimum magnetometer values in microgauss. +/-32752 is the maximum range of the
+ * data registers (slightly less than the range of int16). This works out to +/- 49,128,000 uGs
+ */
+#define AKM09918C_MAGN_MAX_MICRO_GAUSS (AKM09918C_MAGN_MAX_DATA_REG * AKM09918C_MICRO_GAUSS_PER_BIT)
+#define AKM09918C_MAGN_MIN_MICRO_GAUSS (AKM09918C_MAGN_MIN_DATA_REG * AKM09918C_MICRO_GAUSS_PER_BIT)
 
 struct akm09918c_data {
 	int16_t x_sample;

tests/drivers/sensor/akm09918c/src/main.c

@@ -10,6 +10,7 @@
 #include <zephyr/drivers/sensor.h>
 #include <zephyr/ztest.h>
 
+#include "akm09918c.h"
 #include "akm09918c_emul.h"
 #include "akm09918c_reg.h"
 
@@ -72,19 +73,19 @@ static void test_fetch_magnetic_field(const struct akm09918c_fixture *fixture,
 
 	/* Assert the data is within 0.000005 Gauss */
 	actual_ugauss = values[0].val1 * INT64_C(1000000) + values[0].val2;
-	expect_ugauss = magn_percent[0] * INT64_C(500);
+	expect_ugauss = magn_percent[0] * AKM09918C_MICRO_GAUSS_PER_BIT;
 	zassert_within(expect_ugauss, actual_ugauss, INT64_C(5),
 		       "(X) expected %" PRIi64 " micro-gauss, got %" PRIi64 " micro-gauss",
 		       expect_ugauss, actual_ugauss);
 
 	actual_ugauss = values[1].val1 * INT64_C(1000000) + values[1].val2;
-	expect_ugauss = magn_percent[1] * INT64_C(500);
+	expect_ugauss = magn_percent[1] * AKM09918C_MICRO_GAUSS_PER_BIT;
 	zassert_within(expect_ugauss, actual_ugauss, INT64_C(5),
 		       "(Y) expected %" PRIi64 " micro-gauss, got %" PRIi64 " micro-gauss",
 		       expect_ugauss, actual_ugauss);
 
 	actual_ugauss = values[2].val1 * INT64_C(1000000) + values[2].val2;
-	expect_ugauss = magn_percent[2] * INT64_C(500);
+	expect_ugauss = magn_percent[2] * AKM09918C_MICRO_GAUSS_PER_BIT;
 	zassert_within(expect_ugauss, actual_ugauss, INT64_C(5),
 		       "(Z) expected %" PRIi64 " micro-gauss, got %" PRIi64 " micro-gauss",
 		       expect_ugauss, actual_ugauss);
@@ -94,9 +95,9 @@ ZTEST_F(akm09918c, test_fetch_magn)
 {
 	/* Use (0.25, -0.33..., 0.91) as the factors */
 	const int16_t magn_percent[3] = {
-		INT16_C(32752) / INT16_C(4),
-		INT16_C(-32751) / INT16_C(3),
-		(int16_t)(INT16_C(32752) * INT32_C(91) / INT32_C(100)),
+		INT16_C(AKM09918C_MAGN_MAX_DATA_REG) / INT16_C(4),
+		INT16_C(AKM09918C_MAGN_MIN_DATA_REG) / INT16_C(3),
+		(int16_t)(INT16_C(AKM09918C_MAGN_MAX_DATA_REG) * INT32_C(91) / INT32_C(100)),
 	};
 
 	test_fetch_magnetic_field(fixture, magn_percent);