drivers: sensor: add MAX31855

add MAX31855 cold-junction compensated thermocouple-to-digital
converter sensor driver and sample

Signed-off-by: Garrett Battaglia <garrett@garrettbattaglia.com>

drivers/sensor/CMakeLists.txt

@@ -68,6 +68,7 @@ add_subdirectory_ifdef(CONFIG_LSM9DS0_MFD	lsm9ds0_mfd)
 add_subdirectory_ifdef(CONFIG_MAX17055		max17055)
 add_subdirectory_ifdef(CONFIG_MAX17262		max17262)
 add_subdirectory_ifdef(CONFIG_MAX30101		max30101)
+add_subdirectory_ifdef(CONFIG_MAX31855		max31855)
 add_subdirectory_ifdef(CONFIG_MAX31875		max31875)
 add_subdirectory_ifdef(CONFIG_MAX44009		max44009)
 add_subdirectory_ifdef(CONFIG_MAX6675		max6675)

drivers/sensor/Kconfig

@@ -177,6 +177,8 @@ source "drivers/sensor/max17262/Kconfig"
 
 source "drivers/sensor/max30101/Kconfig"
 
+source "drivers/sensor/max31855/Kconfig"
+
 source "drivers/sensor/max31875/Kconfig"
 
 source "drivers/sensor/max44009/Kconfig"

drivers/sensor/max31855/CMakeLists.txt

@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: Apache-2.0
+
+zephyr_library()
+
+zephyr_library_sources_ifdef(CONFIG_MAX31855 max31855.c)

drivers/sensor/max31855/Kconfig

@@ -0,0 +1,12 @@
+# MAX31855 cold-junction compensated thermocouple-to-digital converter configuration options
+
+# Copyright (c) 2020 Christian Hirsch
+# SPDX-License-Identifier: Apache-2.0
+
+config MAX31855
+	bool "MAX31855 sensor"
+	default y
+	depends on DT_HAS_MAXIM_MAX31855_ENABLED
+	select SPI
+	help
+	  Enable driver for MAX31855 SPI-based Cold-Junction Compensated thermocouple-to-Digital Converter.

drivers/sensor/max31855/max31855.c

@@ -0,0 +1,132 @@
+/*
+ * Copyright (c) 2020 Christian Hirsch
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+#define DT_DRV_COMPAT maxim_max31855
+
+#include <zephyr/kernel.h>
+#include <zephyr/drivers/sensor.h>
+#include <zephyr/init.h>
+#include <zephyr/drivers/gpio.h>
+#include <zephyr/sys/byteorder.h>
+#include <zephyr/sys/__assert.h>
+#include <zephyr/drivers/spi.h>
+#include <zephyr/logging/log.h>
+#include <zephyr/types.h>
+#include <zephyr/device.h>
+
+#define THERMOCOUPLE_TEMPERATURE_POS 18
+#define INTERNAL_TEMPERATURE_POS     4
+#define THERMOCOUPLE_SIGN_BITS	     0xffff2000
+#define INTERNAL_SIGN_BITS	     0xfffff800
+#define THERMOCOUPLE_RESOLUTION	     25
+#define INTERNAL_RESOLUTION	     625
+
+LOG_MODULE_REGISTER(MAX31855, CONFIG_SENSOR_LOG_LEVEL);
+
+struct max31855_config {
+	struct spi_dt_spec spi;
+};
+
+struct max31855_data {
+	uint32_t sample;
+};
+
+static int max31855_sample_fetch(const struct device *dev, enum sensor_channel chan)
+{
+	struct max31855_data *data = dev->data;
+	const struct max31855_config *config = dev->config;
+	int ret;
+
+	__ASSERT_NO_MSG(chan == SENSOR_CHAN_ALL);
+
+	struct spi_buf rx_buf = {
+		.buf = &(data->sample),
+		.len = sizeof(data->sample),
+	};
+	const struct spi_buf_set rx = {.buffers = &rx_buf, .count = 1};
+
+	ret = spi_read_dt(&config->spi, &rx);
+	if (ret < 0) {
+		LOG_ERR("max31855_read FAIL %d", ret);
+		return ret;
+	}
+
+	return 0;
+}
+
+static int max31855_channel_get(const struct device *dev, enum sensor_channel chan,
+				struct sensor_value *val)
+{
+	struct max31855_data *data = dev->data;
+	uint32_t temp = sys_be32_to_cpu(data->sample);
+
+	if (temp & BIT(16)) {
+		return -EIO;
+	}
+
+	switch (chan) {
+
+	case SENSOR_CHAN_AMBIENT_TEMP:
+		temp = (temp >> THERMOCOUPLE_TEMPERATURE_POS) & 0x3fff;
+
+		/* if sign bit is set, make value negative */
+		if (temp & BIT(14)) {
+			temp |= THERMOCOUPLE_SIGN_BITS;
+		}
+
+		temp = temp * THERMOCOUPLE_RESOLUTION;
+
+		val->val1 = temp / 100;
+		val->val2 = (temp - val->val1 * 100) * 10000;
+		break;
+
+	case SENSOR_CHAN_DIE_TEMP:
+		temp = (temp >> INTERNAL_TEMPERATURE_POS) & 0xfff;
+
+		/* if sign bit is set, make value negative */
+		if (temp & BIT(12)) {
+			temp |= INTERNAL_SIGN_BITS;
+		}
+
+		temp = temp * INTERNAL_RESOLUTION;
+
+		val->val1 = temp / 10000;
+		val->val2 = (temp - val->val1 * 10000) * 100;
+		break;
+
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static const struct sensor_driver_api max31855_api = {
+	.sample_fetch = max31855_sample_fetch,
+	.channel_get = max31855_channel_get,
+};
+
+static int max31855_init(const struct device *dev)
+{
+	const struct max31855_config *config = dev->config;
+
+	if (!spi_is_ready_dt(&config->spi)) {
+		LOG_ERR("SPI bus is not ready");
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
+#define MAX31855_INIT(n)                                                                           \
+	static struct max31855_data max31855_data_##n;                                             \
+	static const struct max31855_config max31855_config_##n = {                                \
+		.spi = SPI_DT_SPEC_INST_GET(n, SPI_OP_MODE_MASTER | SPI_WORD_SET(8U), 0U),         \
+	};                                                                                         \
+	SENSOR_DEVICE_DT_INST_DEFINE(n, &max31855_init, NULL, &max31855_data_##n,                  \
+				     &max31855_config_##n, POST_KERNEL,                            \
+				     CONFIG_SENSOR_INIT_PRIORITY, &max31855_api);
+
+DT_INST_FOREACH_STATUS_OKAY(MAX31855_INIT)

dts/bindings/sensor/maxim,max31855-spi.yaml

@@ -0,0 +1,8 @@
+# Copyright (c) 2020, Christian Hirsch
+# SPDX-License-Identifier: Apache-2.0
+
+description: MAX31855 SPI-based cold-junction compensated thermocouple-to-digital converter.
+
+compatible: "maxim,max31855"
+
+include: [sensor-device.yaml, spi-device.yaml]

tests/drivers/build_all/sensor/spi.dtsi

@@ -337,3 +337,9 @@ test_spi_icm426888: icm42688@28 {
 	gyro-hz = <32000>;
 	gyro-fs = <2000>;
 };
+
+test_spi_max31855: max31855@29 {
+	compatible = "maxim,max31855";
+	reg = <0x29>;
+	spi-max-frequency = <0>;
+};