drivers: sensor: add support for MAX6675

Add support for MAX6675 cold-junction-compensated K-thermocouple to
digital converter.

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>

drivers/sensor/CMakeLists.txt

@@ -52,6 +52,7 @@ add_subdirectory_ifdef(CONFIG_LSM9DS0_MFD	lsm9ds0_mfd)
 add_subdirectory_ifdef(CONFIG_MAX17055		max17055)
 add_subdirectory_ifdef(CONFIG_MAX30101		max30101)
 add_subdirectory_ifdef(CONFIG_MAX44009		max44009)
+add_subdirectory_ifdef(CONFIG_MAX6675		max6675)
 add_subdirectory_ifdef(CONFIG_MCP9808		mcp9808)
 add_subdirectory_ifdef(CONFIG_MPR			mpr)
 add_subdirectory_ifdef(CONFIG_MPU6050		mpu6050)

drivers/sensor/Kconfig

@@ -142,6 +142,8 @@ source "drivers/sensor/max30101/Kconfig"
 
 source "drivers/sensor/max44009/Kconfig"
 
+source "drivers/sensor/max6675/Kconfig"
+
 source "drivers/sensor/mchp_tach_xec/Kconfig"
 
 source "drivers/sensor/mcp9808/Kconfig"

drivers/sensor/max6675/CMakeLists.txt

@@ -0,0 +1,5 @@
+# Copyright (c) 2021 Teslabs Engineering S.L.
+# SPDX-License-Identifier: Apache-2.0
+
+zephyr_library()
+zephyr_library_sources_ifdef(CONFIG_MAX6675 max6675.c)

drivers/sensor/max6675/Kconfig

@@ -0,0 +1,9 @@
+# Copyright (c) 2021 Teslabs Engineering S.L.
+# SPDX-License-Identifier: Apache-2.0
+
+config MAX6675
+	bool "MAX6675 K-thermocouple to digital converter"
+	depends on SPI
+	help
+	  Enable MAX6675 cold-junction-compensated K-thermocouple to digital
+	  converter.

drivers/sensor/max6675/max6675.c

@@ -0,0 +1,144 @@
+/*
+ * Copyright (c) 2021 Teslabs Engineering S.L.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#define DT_DRV_COMPAT maxim_max6675
+
+#include <drivers/sensor.h>
+#include <drivers/spi.h>
+#include <sys/byteorder.h>
+
+#include <logging/log.h>
+LOG_MODULE_REGISTER(max6675, CONFIG_SENSOR_LOG_LEVEL);
+
+/** Thermocouple input bit (goes high if thermocouple is disconnected). */
+#define THERMOCOUPLE_INPUT BIT(2)
+/** Temperature position. */
+#define TEMPERATURE_POS 3U
+/** Temperature resolution (cDeg/LSB). */
+#define TEMPERATURE_RES 25U
+
+struct max6675_config {
+	const char *spi_label;
+	struct spi_config spi_config;
+	const char *spi_cs_label;
+	gpio_pin_t spi_cs_pin;
+	gpio_dt_flags_t spi_cs_flags;
+};
+
+struct max6675_data {
+	const struct device *spi;
+	struct spi_cs_control cs_ctrl;
+	uint16_t sample;
+};
+
+static int max6675_sample_fetch(const struct device *dev,
+				enum sensor_channel chan)
+{
+	struct max6675_data *data = dev->data;
+	const struct max6675_config *config = dev->config;
+
+	int ret;
+	uint8_t buf_rx[2];
+	const struct spi_buf rx_buf = {
+		.buf = buf_rx,
+		.len = ARRAY_SIZE(buf_rx)
+	};
+	const struct spi_buf_set rx_bufs = {
+		.buffers = &rx_buf,
+		.count = 1U
+	};
+
+	if (chan != SENSOR_CHAN_ALL && chan != SENSOR_CHAN_AMBIENT_TEMP) {
+		return -ENOTSUP;
+	}
+
+	ret = spi_read(data->spi, &config->spi_config, &rx_bufs);
+	if (ret < 0) {
+		return ret;
+	}
+
+	data->sample = sys_get_be16(buf_rx);
+
+	if (data->sample & THERMOCOUPLE_INPUT) {
+		LOG_INF("Thermocouple not connected");
+		return -ENOENT;
+	}
+
+	return 0;
+}
+
+static int max6675_channel_get(const struct device *dev, enum sensor_channel chan,
+			      struct sensor_value *val)
+{
+	struct max6675_data *data = dev->data;
+
+	int32_t temperature;
+
+	if (chan != SENSOR_CHAN_AMBIENT_TEMP) {
+		return -ENOTSUP;
+	}
+
+	temperature = (data->sample >> TEMPERATURE_POS) * TEMPERATURE_RES;
+	val->val1 = temperature / 100;
+	val->val2 = (temperature - val->val1 * 100) * 10000;
+
+	return 0;
+}
+
+static const struct sensor_driver_api max6675_api = {
+	.sample_fetch = &max6675_sample_fetch,
+	.channel_get = &max6675_channel_get,
+};
+
+static int max6675_init(const struct device *dev)
+{
+	struct max6675_data *data = dev->data;
+	const struct max6675_config *config = dev->config;
+
+	data->spi = device_get_binding(config->spi_label);
+	if (data->spi == NULL) {
+		LOG_ERR("Could not get SPI device %s", config->spi_label);
+		return -ENODEV;
+	}
+
+	data->cs_ctrl.gpio_dev = device_get_binding(config->spi_cs_label);
+	if (data->cs_ctrl.gpio_dev != NULL) {
+		data->cs_ctrl.gpio_pin = config->spi_cs_pin;
+		data->cs_ctrl.gpio_dt_flags = config->spi_cs_flags;
+		data->cs_ctrl.delay = 0U;
+	}
+
+	return 0;
+}
+
+#define MAX6675_INIT(n)							       \
+	static struct max6675_data max6675_data_##n;			       \
+									       \
+	static const struct max6675_config max6675_config_##n = {	       \
+		.spi_label = DT_INST_BUS_LABEL(n),			       \
+		.spi_config = {						       \
+			.frequency = DT_INST_PROP_OR(n, spi_max_frequency, 0U),\
+			.operation = SPI_OP_MODE_MASTER | SPI_WORD_SET(8U),    \
+			.slave = DT_INST_REG_ADDR(n),			       \
+			.cs = &max6675_data_##n.cs_ctrl,		       \
+		},							       \
+		.spi_cs_label = UTIL_AND(				       \
+			DT_INST_SPI_DEV_HAS_CS_GPIOS(n),		       \
+			DT_INST_SPI_DEV_CS_GPIOS_LABEL(n)),		       \
+		.spi_cs_pin = UTIL_AND(					       \
+			DT_INST_SPI_DEV_HAS_CS_GPIOS(n),		       \
+			DT_INST_SPI_DEV_CS_GPIOS_PIN(n)),		       \
+		.spi_cs_flags = UTIL_AND(				       \
+			DT_INST_SPI_DEV_HAS_CS_GPIOS(n),		       \
+			DT_INST_SPI_DEV_CS_GPIOS_FLAGS(n)),		       \
+	};								       \
+									       \
+	DEVICE_DT_INST_DEFINE(n, &max6675_init, device_pm_control_nop,	       \
+			      &max6675_data_##n, &max6675_config_##n,	       \
+			      POST_KERNEL, CONFIG_SENSOR_INIT_PRIORITY,	       \
+			      &max6675_api);
+
+DT_INST_FOREACH_STATUS_OKAY(MAX6675_INIT)

dts/bindings/sensor/maxim,max6675.yaml

@@ -0,0 +1,8 @@
+# Copyright (c) 2021, Teslabs Engineering S.L.
+# SPDX-License-Identifier: Apache-2.0
+
+description: MAX6675 K-thermocouple to digital converter
+
+compatible: "maxim,max6675"
+
+include: spi-device.yaml