drivers/sensor: si7006: Fix math for calculating sensor values (0f219e1e) · Commits · Wenxi XU / zephyr

drivers/sensor/silabs/si7006/si7006.c

+50 −16

Original line number	Diff line number	Diff line
		@@ -14,6 +14,7 @@
		#include <zephyr/drivers/i2c.h>
		#include <stdio.h>
		#include <stdlib.h>
		#include <zephyr/sys/util.h>
		#include "si7006.h"
		#include <zephyr/logging/log.h>

		@@ -112,25 +113,58 @@ static int si7006_channel_get(const struct device *dev,
		struct si7006_data *si_data = dev->data;

		if (chan == SENSOR_CHAN_AMBIENT_TEMP) {
		/* Raw formula: (temp * 175.72) / 65536 - 46.85
		* To use integer math, scale the 175.72 factor by 128 and move the offset to
		* inside the division. This gives us:
		*
		* (temp * 175.72 * 128 - 46.86 * 128 * 65536) / (65536 * 128)
		* The constants can be calculated now:
		* (temp * 22492 - 393006285) / 2^23
		*
		* There is a very small amount of round-off error in the factor of 22492. To
		* compenstate, a constant of 5246 is used to center the error about 0, thus
		* reducing the overall MSE.
		*/

		int32_t temp_ucelcius = (((17572 * (int32_t)si_data->temperature)
		/ 65536) - 4685) * 10000;

		val->val1 = temp_ucelcius / 1000000;
		val->val2 = temp_ucelcius % 1000000;
		/* Temperature value times two to the 23rd power, i.e. temp_23 = temp << 23 */
		const int32_t temp_23 = si_data->temperature * 22492 - (393006285 - 5246);
		/* Integer component of temperature */
		int32_t temp_int = temp_23 >> 23;
		/* Fractional component of temperature */
		int32_t temp_frac = temp_23 & BIT_MASK(23);

		/* Deal with the split twos-complement / BCD format oddness with negatives */
		if (temp_23 < 0) {
		temp_int += 1;
		temp_frac -= BIT(23);
		}
		val->val1 = temp_int;
		/* Remove a constant factor of 64 from (temp_frac * 1000000) >> 23 */
		val->val2 = (temp_frac * 15625ULL) >> 17;

		LOG_DBG("temperature = val1:%d, val2:%d", val->val1, val->val2);
		LOG_DBG("temperature %u = val1:%d, val2:%d", si_data->temperature,
		val->val1, val->val2);

		return 0;
		} else if (chan == SENSOR_CHAN_HUMIDITY) {
		/* Humidity times two to the 16th power. Offset of -6 not applied yet. */
		const uint32_t rh_16 = si_data->humidity * 125U;
		/* Integer component of humidity */
		const int16_t rh_int = rh_16 >> 16;
		/* Fraction component of humidity */
		const uint16_t rh_frac = rh_16 & BIT_MASK(16);

		val->val1 = rh_int - 6; /* Apply offset now */
		/* Remove a constant factor of 64 from (rh_frac * 1000000) >> 16 */
		val->val2 = (rh_frac * 15625) >> 10;

		/* Deal with the split twos-complement / BCD format oddness with negatives */
		if (val->val1 < 0) {
		val->val1 += 1;
		val->val2 -= 1000000;
		}

		int32_t relative_humidity = (((125 * (int32_t)si_data->humidity)
		/ 65536) - 6) * 1000000;

		val->val1 = relative_humidity / 1000000;
		val->val2 = relative_humidity % 1000000;

		LOG_DBG("humidity = val1:%d, val2:%d", val->val1, val->val2);
		LOG_DBG("humidity %u = val1:%d, val2:%d", si_data->humidity, val->val1, val->val2);

		return 0;
		} else {

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