drivers: add max31855

drivers/include/max31855.h

@@ -0,0 +1,135 @@
+/*
+ * Copyright (C) 2024 HAW Hamburg
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @defgroup    drivers_max31855 MAX31855 Thermocouple-to-Digital Converter driver
+ * @ingroup     drivers_sensors
+ * @brief       Driver for the SPI Thermocouple-to-Digital Converter MAX31855.
+ *
+ *              The MAX31855 performs cold-junction compensation and digitizes
+ *              the signal from a K-, J-, N-, T-, S-, R-, or E-type
+ *              thermocouple. The data is output in a signed 14-bit,
+ *              SPI-compatible, read-only format. This converter resolves
+ *              temperatures to 0.25°C, allows readings as high as +1800°C and
+ *              as low as -270°C, and exhibits thermocouple accuracy of ±2°C
+ *              for temperatures ranging from -200°C to +700°C for K-type
+ *              thermocouples.
+ *
+ * @note See the datasheet for more information:
+ * https://www.analog.com/media/en/technical-documentation/data-sheets/MAX31855.pdf
+ *
+ * @note This driver doesn't require a MOSI line, as the MAX31855 is a read-only.
+ *
+ * @{
+ *
+ * @file
+ *
+ * @author      Leandro Lanzieri <leandro.lanzieri@haw-hamburg.de>
+ */
+
+#ifndef MAX31855_H
+#define MAX31855_H
+
+/* Add header includes here */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include "periph/spi.h"
+
+/* Declare the API of the driver */
+
+/**
+ * @brief   Device initialization parameters
+ */
+typedef struct {
+    spi_t spi;          /**< SPI device */
+    spi_cs_t cs_pin;    /**< Chip select pin */
+} max31855_params_t;
+
+/**
+ * @brief   Device descriptor for the driver
+ */
+typedef struct {
+    const max31855_params_t *params;  /**< device configuration */
+} max31855_t;
+
+/**
+ * @brief   Fault status of the MAX31855
+ */
+typedef enum {
+    MAX31855_FAULT_VCC_SHORT    = 0,    /**< VCC short-circuit */
+    MAX31855_FAULT_GND_SHORT    = 1,    /**< GND short-circuit */
+    MAX31855_FAULT_OPEN_CIRCUIT = 2,    /**< Open circuit */
+    MAX31855_FAULT_NO_FAULT     = 3     /**< No fault */
+} max31855_fault_t;
+
+/**
+ * @brief   Data structure for the MAX31855
+ */
+typedef struct {
+    int32_t thermocouple_temperature;   /**< Thermocouple temperature in centi degrees C */
+    int32_t internal_temperature;       /**< Internal temperature in centi degrees C */
+    max31855_fault_t fault;             /**< Fault status */
+} max31855_data_t;
+
+/**
+ * @brief   Initialize the given device
+ *
+ * @param[inout] dev        Device descriptor of the driver
+ * @param[in]    params     Initialization parameters
+ *
+ * @retval    0 on success
+ * @retval    -ENXIO invalid SPI device
+ * @retval    -EINVAL invalid SPI CS pin/line
+ */
+int max31855_init(max31855_t *dev, const max31855_params_t *params);
+
+/**
+ * @brief   Parse the raw data from the MAX31855 to the data structure
+ *
+ * @param[in]  raw_data    Raw data from the MAX31855
+ * @param[out] data        Pointer to the data structure.
+ *
+ * @pre                    @p data must not be NULL
+ */
+void max31855_raw_to_data(uint32_t raw_data, max31855_data_t *data);
+
+/**
+ * @brief   Read data from the MAX31855. This is a shortcut to read raw data
+ *        and parse it to the data structure.
+ *
+ * @param[in]  dev         Device descriptor of the driver
+ * @param[out] data        Pointer to the data structure.
+ *
+ * @pre                    @p dev and @p data must not be NULL
+ *
+ * @retval   0 on success
+ * @retval   -EIO if there is an error detected by the MAX31855. For a detailed
+ *      error description, check the fault field of the data structure. On this
+ *      case, temperature fields are not valid.
+ */
+int max31855_read(max31855_t *dev, max31855_data_t *data);
+
+/**
+ * @brief   Read raw data from the MAX31855
+ *
+ * @param[in]  dev         Device descriptor of the driver
+ * @param[out] data        Pointer where to store the raw data.
+ *
+ * @pre                    @p dev and @p data must not be NULL
+ */
+void max31855_read_raw(max31855_t *dev, uint32_t *data);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* MAX31855_H */
+/** @} */

drivers/max31855/Makefile

@@ -0,0 +1 @@
+include $(RIOTBASE)/Makefile.base

drivers/max31855/Makefile.dep

@@ -0,0 +1 @@
+FEATURES_REQUIRED += periph_spi

drivers/max31855/Makefile.include

@@ -0,0 +1,2 @@
+USEMODULE_INCLUDES_max31855 := $(LAST_MAKEFILEDIR)/include
+USEMODULE_INCLUDES += $(USEMODULE_INCLUDES_max31855)

drivers/max31855/include/max31855_constants.h

@@ -0,0 +1,173 @@
+/*
+ * Copyright (C) 2024 HAW Hamburg
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     drivers_max31855
+ * @{
+ *
+ * @file
+ * @brief       Internal addresses, registers and constants
+ *
+ * @author      Leandro Lanzieri <leandro.lanzieri@haw-hamburg.de>
+ */
+
+#ifndef MAX31855_CONSTANTS_H
+#define MAX31855_CONSTANTS_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief Size of the data read from the MAX31855 in bytes.
+ */
+#define MAX31855_DATA_SIZE (4)
+
+/**
+ * @brief Shift value for the thermocouple sign bit.
+ */
+#define MAX31855_THERMOCOUPLE_SIGN_SHIFT (31)
+
+/**
+   @brief Mask value for the thermocouple sign bit.
+ */
+#define MAX31855_THERMOCOUPLE_SIGN_MASK (1UL << MAX31855_THERMOCOUPLE_SIGN_SHIFT)
+
+/**
+ * @brief Shift value for the thermocouple integer bits.
+ */
+#define MAX31855_THERMOCOUPLE_INTEGER_SHIFT (20)
+
+/**
+ * @brief Mask value for the thermocouple integer bits.
+ */
+#define MAX31855_THERMOCOUPLE_INTEGER_MASK (0x7FFUL << MAX31855_THERMOCOUPLE_INTEGER_SHIFT)
+
+/**
+ * @brief Shift value for the thermocouple fractional half degree bit.
+ */
+#define MAX31855_THERMOCOUPLE_FRACTIONAL_HALF_SHIFT (19)
+
+/**
+ * @brief Mask value for the thermocouple fractional half degree bit.
+ */
+#define MAX31855_THERMOCOUPLE_FRACTIONAL_HALF_MASK (1UL << MAX31855_THERMOCOUPLE_FRACTIONAL_HALF_SHIFT)
+
+/**
+ * @brief Shift value for the thermocouple fractional quarter degree bit.
+ */
+#define MAX31855_THERMOCOUPLE_FRACTIONAL_QUARTER_SHIFT (18)
+
+/**
+ * @brief Mask value for the thermocouple fractional quarter degree bit.
+ */
+#define MAX31855_THERMOCOUPLE_FRACTIONAL_QUARTER_MASK (1UL << MAX31855_THERMOCOUPLE_FRACTIONAL_QUARTER_SHIFT)
+
+/**
+ * @brief Shift value for the internal sign bit.
+ */
+#define MAX31855_INTERNAL_SIGN_SHIFT (15)
+
+/**
+   @brief Mask value for the internal sign bit.
+ */
+#define MAX31855_INTERNAL_SIGN_MASK (1UL << MAX31855_INTERNAL_SIGN_SHIFT)
+
+/**
+ * @brief Shift value for the internal integer bits.
+ */
+#define MAX31855_INTERNAL_INTEGER_SHIFT (8)
+
+/**
+ * @brief Mask value for the internal integer bits.
+ */
+#define MAX31855_INTERNAL_INTEGER_MASK (0x7FUL << MAX31855_INTERNAL_INTEGER_SHIFT)
+
+/**
+ * @brief Shift value for the internal fractional half degree bit.
+ */
+#define MAX31855_INTERNAL_FRACTIONAL_HALF_SHIFT (7)
+
+/**
+ * @brief Mask value for the internal fractional half degree bit.
+ */
+#define MAX31855_INTERNAL_FRACTIONAL_HALF_MASK (1UL << MAX31855_INTERNAL_FRACTIONAL_HALF_SHIFT)
+
+/**
+ * @brief Shift value for the internal fractional quarter degree bit.
+ */
+#define MAX31855_INTERNAL_FRACTIONAL_QUARTER_SHIFT (6)
+
+/**
+ * @brief Mask value for the internal fractional quarter degree bit.
+ */
+#define MAX31855_INTERNAL_FRACTIONAL_QUARTER_MASK (1UL << MAX31855_INTERNAL_FRACTIONAL_QUARTER_SHIFT)
+
+/**
+ * @brief Shift value for the internal fractional eighth degree bit.
+ */
+#define MAX31855_INTERNAL_FRACTIONAL_EIGHTH_SHIFT (5)
+
+/**
+ * @brief Shift value for the internal fractional eighth degree bit.
+ */
+#define MAX31855_INTERNAL_FRACTIONAL_EIGHTH_MASK (1UL << MAX31855_INTERNAL_FRACTIONAL_EIGHTH_SHIFT)
+
+/**
+ * @brief Shift value for the internal fractional sixteenth degree bit.
+ */
+#define MAX31855_INTERNAL_FRACTIONAL_SIXTEENTH_SHIFT (4)
+
+/**
+ * @brief Shift value for the internal fractional sixteenth degree bit.
+ */
+#define MAX31855_INTERNAL_FRACTIONAL_SIXTEENTH_MASK (1UL << MAX31855_INTERNAL_FRACTIONAL_SIXTEENTH_SHIFT)
+
+/**
+ * @brief Shift value for the fault bit indicating a VCC short.
+ */
+#define MAX31855_FAULT_VCC_SHORT_SHIFT (2)
+
+/**
+ * @brief Mask value for the fault bit indicating a VCC short.
+ */
+#define MAX31855_FAULT_VCC_SHORT_MASK (1UL << MAX31855_FAULT_VCC_SHORT_SHIFT)
+
+/**
+ * @brief Shift value for the fault bit indicating a GND short.
+ */
+#define MAX31855_FAULT_GND_SHORT_SHIFT (1)
+
+/**
+ * @brief Mask value for the fault bit indicating a GND short.
+ */
+#define MAX31855_FAULT_GND_SHORT_MASK (1UL << MAX31855_FAULT_GND_SHORT_SHIFT)
+
+/**
+ * @brief Shift value for the fault bit indicating an open circuit.
+ */
+#define MAX31855_FAULT_OPEN_CIRCUIT_SHIFT (0)
+
+/**
+ * @brief Mask value for the fault bit indicating an open circuit.
+ */
+#define MAX31855_FAULT_OPEN_CIRCUIT_MASK (1UL << MAX31855_FAULT_OPEN_CIRCUIT_SHIFT)
+
+/**
+ * @brief Mask value for the fault bits.
+ */
+#define MAX31855_FAULT_MASK (MAX31855_FAULT_VCC_SHORT_MASK | \
+                             MAX31855_FAULT_GND_SHORT_MASK | \
+                             MAX31855_FAULT_OPEN_CIRCUIT_MASK)
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* MAX31855_CONSTANTS_H */
+/** @} */

drivers/max31855/include/max31855_params.h

@@ -0,0 +1,86 @@
+/*
+ * Copyright (C) 2024 HAW Hamburg
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     drivers_max31855
+ *
+ * @{
+ * @file
+ * @brief       Default configuration for the MAX31855 driver
+ *
+ * @author      Leandro Lanzieri <leandro.lanzieri@haw-hamburg.de>
+ */
+
+#ifndef MAX31855_PARAMS_H
+#define MAX31855_PARAMS_H
+
+#include "board.h"
+#include "saul_reg.h"
+
+#include "max31855.h"
+#include "max31855_constants.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @name    Default configuration for the MAX31855 driver
+ * @{
+ */
+/**
+ * @brief    Default SPI bus for the MAX31855 driver
+ */
+#ifndef MAX31855_PARAM_PARAM_SPI
+#define MAX31855_PARAM_PARAM_SPI        (SPI_DEV(0))
+#endif
+/**
+ * @brief    Default CS pin for the MAX31855 driver
+ */
+#ifndef MAX31855_PARAM_PARAM_CS_PIN
+#define MAX31855_PARAM_PARAM_CS_PIN     (GPIO_PIN(0, 4))
+#endif
+/**
+ * @brief    Default parameters for the MAX31855 driver
+ */
+#ifndef MAX31855_PARAMS
+#define MAX31855_PARAMS {                   \
+            .spi = MAX31855_PARAM_PARAM_SPI,        \
+            .cs_pin = MAX31855_PARAM_PARAM_CS_PIN,  \
+}
+#endif
+/**
+ * @brief    Default SAUL info for the MAX31855 driver
+ */
+#ifndef MAX31855_SAULINFO
+#define MAX31855_SAULINFO { .name = "max31855_thermo" },{ .name = "max31855_internal" }
+#endif
+/**@}*/
+
+/**
+ * @brief   Configuration structs for the MAX31855 driver
+ */
+static const max31855_params_t max31855_params[] =
+{
+    MAX31855_PARAMS
+};
+
+/**
+ * @brief   Allocate and configure entries to the SAUL registry
+ */
+static const saul_reg_info_t max31855_saul_info[] =
+{
+    MAX31855_SAULINFO
+};
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* MAX31855_PARAMS_H */
+/** @} */

drivers/max31855/max31855.c

@@ -0,0 +1,156 @@
+/*
+ * Copyright (C) 2024 HAW Hamburg
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     drivers_max31855
+ * @{
+ *
+ * @file
+ * @brief       Device driver implementation for the drivers_sensors
+ *
+ * @author      Leandro Lanzieri <leandro.lanzieri@haw-hamburg.de>
+ *
+ * @}
+ */
+
+#include <assert.h>
+#include <errno.h>
+#include <stdio.h>
+
+#include "byteorder.h"
+#include "log.h"
+
+#include "max31855.h"
+#include "max31855_constants.h"
+#include "max31855_params.h"
+
+
+void _raw_data_to_thermocouple_temperature(uint32_t raw_data, int32_t *temperature)
+{
+    assert(temperature);
+
+    int32_t is_negative = raw_data & MAX31855_THERMOCOUPLE_SIGN_MASK;
+
+    if (is_negative) {
+        raw_data = ~raw_data + 1;
+    }
+
+    *temperature = (raw_data & MAX31855_THERMOCOUPLE_INTEGER_MASK) >>
+                        MAX31855_THERMOCOUPLE_INTEGER_SHIFT;
+
+    /* convert to centi degC */
+    *temperature = *temperature * 100;
+
+    /* add fractional parts */
+    *temperature += (raw_data & MAX31855_THERMOCOUPLE_FRACTIONAL_HALF_MASK) ? 50 : 0;
+    *temperature += (raw_data & MAX31855_THERMOCOUPLE_FRACTIONAL_QUARTER_MASK) ? 25 : 0;
+
+    if (is_negative) {
+        *temperature *= -1;
+    }
+}
+
+void _raw_data_to_internal_temperature(uint32_t raw_data, int32_t *temperature)
+{
+    assert(temperature);
+
+    int32_t is_negative = raw_data & MAX31855_INTERNAL_SIGN_MASK;
+
+    if (is_negative) {
+        raw_data = ~raw_data + 1;
+    }
+
+    *temperature = (raw_data & MAX31855_INTERNAL_INTEGER_MASK) >> MAX31855_INTERNAL_INTEGER_SHIFT;
+
+    /* convert to centi degC */
+    *temperature = *temperature * 100;
+
+    /* add fractional parts */
+    *temperature += (raw_data & MAX31855_INTERNAL_FRACTIONAL_HALF_MASK) ? 50 : 0;
+    *temperature += (raw_data & MAX31855_INTERNAL_FRACTIONAL_QUARTER_MASK) ? 25 : 0;
+    *temperature += (raw_data & MAX31855_INTERNAL_FRACTIONAL_EIGHTH_MASK) ? 12 : 0;
+    *temperature += (raw_data & MAX31855_INTERNAL_FRACTIONAL_SIXTEENTH_MASK) ? 6 : 0;
+
+    if (is_negative) {
+        *temperature *= -1;
+    }
+}
+
+void _raw_data_to_fault(uint32_t raw_data, max31855_fault_t *fault)
+{
+    assert(fault);
+
+    switch (raw_data & MAX31855_FAULT_MASK) {
+        case MAX31855_FAULT_VCC_SHORT_MASK:
+            *fault = MAX31855_FAULT_VCC_SHORT;
+            break;
+        case MAX31855_FAULT_GND_SHORT_MASK:
+            *fault = MAX31855_FAULT_GND_SHORT;
+            break;
+        case MAX31855_FAULT_OPEN_CIRCUIT_MASK:
+            *fault = MAX31855_FAULT_OPEN_CIRCUIT;
+            break;
+        default:
+            *fault = MAX31855_FAULT_NO_FAULT;
+            break;
+    }
+}
+
+int max31855_init(max31855_t *dev, const max31855_params_t *params)
+{
+    assert(dev);
+    assert(params);
+    dev->params = params;
+
+    int ret = spi_init_cs(dev->params->spi, dev->params->cs_pin);
+
+    if (ret < 0) {
+        LOG_ERROR("Failed to initialize MAX31855\n");
+        return ret;
+    }
+
+    return 0;
+}
+
+void max31855_read_raw(max31855_t *dev, uint32_t *data)
+{
+    assert(dev);
+    assert(data);
+
+    uint8_t buffer[MAX31855_DATA_SIZE] = { 0 };
+    spi_acquire(dev->params->spi, dev->params->cs_pin, SPI_MODE_0, SPI_CLK_5MHZ);
+    spi_transfer_bytes(dev->params->spi, dev->params->cs_pin, false, NULL, buffer, sizeof(buffer));
+    spi_release(dev->params->spi);
+
+    *data = byteorder_bebuftohl(buffer);
+}
+
+void max31855_raw_to_data(uint32_t raw_data, max31855_data_t *data)
+{
+    assert(data);
+
+    _raw_data_to_thermocouple_temperature(raw_data, &data->thermocouple_temperature);
+    _raw_data_to_internal_temperature(raw_data, &data->internal_temperature);
+    _raw_data_to_fault(raw_data, &data->fault);
+}
+
+int max31855_read(max31855_t *dev, max31855_data_t *data)
+{
+    assert(dev && data);
+
+    uint32_t raw_data;
+    max31855_read_raw(dev, &raw_data);
+    max31855_raw_to_data(raw_data, data);
+
+    if (data->fault != MAX31855_FAULT_NO_FAULT) {
+        LOG_ERROR("MAX31855 fault: %d\n", data->fault);
+        return -EIO;
+    }
+
+    return 0;
+}

drivers/max31855/max31855_saul.c

@@ -0,0 +1,69 @@
+/*
+ * Copyright (C) 2024 HAW Hamburg
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     drivers_max31855
+ * @{
+ *
+ * @file
+ * @brief       SAUL adaption for MAX31855 devices
+ *
+ * @author      Leandro Lanzieri <leandro.lanzieri@haw-hamburg.de>
+ *
+ * @}
+ */
+
+#include <string.h>
+
+#include "saul.h"
+#include "phydat.h"
+#include "max31855.h"
+
+static int read_temp(const void *dev, phydat_t *res, bool thermocouple)
+{
+    max31855_data_t data;
+    max31855_read((max31855_t *)dev, &data);
+
+    if (data.fault != MAX31855_FAULT_NO_FAULT) {
+        return -ECANCELED;
+    }
+
+    res->unit = UNIT_TEMP_C;
+    res->scale = -2;
+
+    if (thermocouple) {
+        phydat_fit(res, &data.thermocouple_temperature, 1);
+    }
+    else {
+        phydat_fit(res, &data.internal_temperature, 1);
+    }
+
+    return 1;
+}
+
+static int read_thermo_temp(const void *dev, phydat_t *res)
+{
+    return read_temp(dev, res, true);
+}
+
+static int read_internal_temp(const void *dev, phydat_t *res)
+{
+    return read_temp(dev, res, false);
+}
+
+const saul_driver_t max31855_thermo_temp_saul_driver = {
+    .read = read_thermo_temp,
+    .write = saul_write_notsup,
+    .type = SAUL_SENSE_TEMP
+};
+
+const saul_driver_t max31855_internal_temp_saul_driver = {
+    .read = read_internal_temp,
+    .write = saul_write_notsup,
+    .type = SAUL_SENSE_TEMP
+};

drivers/saul/init_devs/auto_init_max31855.c

@@ -0,0 +1,80 @@
+/*
+ * Copyright (C) 2024 HAW Hamburg
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ *
+ */
+
+/*
+ * @ingroup     sys_auto_init_saul
+ * @{
+ *
+ * @file
+ * @brief       Auto initialization for MAX31855 thermocouple-to-digital converters
+ *
+ * @author      Leandro Lanzieri <leandro.lanzieri@haw-hamburg.de>
+ *
+ * @}
+ */
+
+#include "assert.h"
+#include "log.h"
+#include "saul_reg.h"
+#include "max31855_params.h"
+#include "max31855.h"
+
+/**
+ * @brief   Define the number of configured devices
+ */
+#define MAX31855_NUM     ARRAY_SIZE(max31855_params)
+
+/**
+ * @brief   Allocate memory for the device descriptors
+ */
+static max31855_t max31855_devs[MAX31855_NUM];
+
+/**
+ * @brief   Memory for the SAUL registry entries
+ */
+static saul_reg_t saul_entries[MAX31855_NUM * 2];
+
+/**
+ * @brief   Define the number of saul info
+ */
+#define MAX31855_INFO_NUM ARRAY_SIZE(max31855_saul_info)
+
+/**
+ * @name    Import SAUL endpoints
+ * @{
+ */
+extern const saul_driver_t max31855_thermo_temp_saul_driver;
+extern const saul_driver_t max31855_internal_temp_saul_driver;
+/** @} */
+
+void auto_init_max31855(void)
+{
+    /* each device has thermocouple and internal temperature, needs 2 infos */
+    assert(MAX31855_INFO_NUM == 2 * MAX31855_NUM);
+
+    for (unsigned int i = 0; i < MAX31855_NUM; i++) {
+        LOG_DEBUG("[auto_init_saul] initializing MAX31855 #%u\n", i);
+
+        if (max31855_init(&max31855_devs[i], &max31855_params[i]) != 0) {
+            LOG_ERROR("[auto_init_saul] error initializing MAX31855 #%u\n", i);
+            continue;
+        }
+
+        saul_entries[(i * 2)].dev = &(max31855_devs[i]);
+        saul_entries[(i * 2)].name = max31855_saul_info[(i * 2)].name;
+        saul_entries[(i * 2)].driver = &max31855_thermo_temp_saul_driver;
+
+        saul_entries[(i * 2) + 1].dev = &(max31855_devs[i]);
+        saul_entries[(i * 2) + 1].name = max31855_saul_info[(i * 2) + 1].name;
+        saul_entries[(i * 2) + 1].driver = &max31855_internal_temp_saul_driver;
+
+        saul_reg_add(&(saul_entries[(i * 2)]));
+        saul_reg_add(&(saul_entries[(i * 2) + 1]));
+    }
+}

drivers/saul/init_devs/init.c

@@ -207,6 +207,10 @@ void saul_init_devs(void)
         extern void auto_init_mag3110(void);
         auto_init_mag3110();
     }
+    if (IS_USED(MODULE_MAX31855)) {
+        extern void auto_init_max31855(void);
+        auto_init_max31855();
+    }
     if (IS_USED(MODULE_MCP47XX)) {
         extern void auto_init_mcp47xx(void);
         auto_init_mcp47xx();